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No general strategy for thermostability has been yet established, because the extra stability of thermophiles appears to be the sum of different cumulative stabilizing interactions. In addition, the increase of conformational rigidity observed in many thermophilic proteins, which in some cases disappears when mesophilic and thermophilic proteins are compared at their respective physiological temperatures, suggests that evolutionary adaptation tends to maintain corresponding states with respect to conformational flexibility. In this study, we accomplished a structural analysis of the K18G/R82E Alicyclobacillus acidocaldarius thioredoxin (BacTrx) mutant, which has reduced heat resistance with respect to the thermostable wild-type. Furthermore, we have also achieved a detailed study, carried out at 25, 45, and 65 degrees C, of the backbone dynamics of both the BacTrx and its K18G/R82E mutant. Our findings clearly indicate that the insertion of the two mutations causes a loss of energetically favorable long-range interactions and renders the secondary structure elements of the double mutants more similar to those of the mesophilic Escherichia coli thioredoxin. Moreover, protein dynamics analysis shows that at room temperature the BacTrx, as well as the double mutant, are globally as rigid as the mesophilic thioredoxins; differently, at 65 degrees C, which is in the optimal growth temperature range of A. acidocaldarius, the wild-type retains its rigidity while the double mutant is characterized by a large increase of the amplitude of the internal motions. Finally, our research interestingly shows that fast motions on the pico- to nanosecond time scale are not detrimental to protein stability and provide an entropic stabilization of the native state. This study further confirms that protein thermostability is reached through diverse stabilizing interactions, which have the key role to maintain the structural folding stable and functional at the working temperature.

Let $(G,K)$ be a Gelfand pair, with $G$ a Lie group of polynomial growth, and let $\Sigma\subset{\mathbb R}^\ell$ be a homeomorphic image of the Gelfand spectrum, obtained by choosing a generating system $D_1,\dots,D_\ell$ of $G$-invariant differential operators on $G/K$ and associating to a bounded spherical function $\varphi$ the $\ell$-tuple of its eigenvalues under the action of the $D_j$'s. We say that property (S) holds for $(G,K)$ if the spherical transform maps the bi-$K$-invariant Schwartz space ${\mathcal S}(K\backslash G/K)$ isomorphically onto ${\mathcal S}(\Sigma)$, the space of restrictions to $\Sigma$ of the Schwartz functions on ${\mathbb R}^\ell$. This property is known to hold for many nilpotent pairs, i.e., Gelfand pairs where $G=K\ltimes N$, with $N$ nilpotent. In this paper we enlarge the scope of this analysis outside the range of nilpotent pairs, stating the basic setting for general pairs of polynomial growth and then focussing on strong Gelfand pairs.

Let δ be the Jacobi Laplacian. We study the chaotic and hypercyclic behaviour of the strongly continuous semigroups of operators generated by perturbations of δ with a multiple of the identity on L p spaces. © 2012 Elsevier Inc.

We prove that Huygens’ principle and the principle of equipartition of energy hold for the modified wave equation on odd dimensional Damek–Ricci spaces. We also prove a Paley–Wiener type theorem for the inverse of the Helgason Fourier transform on Damek–Ricci spaces.

The synthesis, physical and analytical characterization, and crystal‐state structural analysis by X‐ray diffraction of three analogues of the Nα‐acylated tripeptide amide tail of oxytocin, each containing a cyclic Cα, α‐ disubstituted glycine at position 2, have been performed. The peptides arc Boc‐L‐Pro‐Ac3c‐Gly‐NH2, Z‐L‐Pro‐Ac5c‐Gly‐NH2 and Z‐L‐Pro‐Ac5c‐Gly‐NH2. While the former is folded in a type‐II β‐turn conformation at the ‐L‐Pro‐Ac3c‐ sequence, the two latter tripeptides form two consecutive (type‐II, type‐I′) β‐turns. The Ac5c‐ and Ac6c‐tripeptides are the first examples of such a highly folded structural combination in a position‐2 analogue of the Nα‐acylated ‐L‐Pro‐L‐Leu‐GIy‐NH2 sequence. Copyright © 1993, Wiley Blackwell. All rights reserved

We prove that a Damek–Ricci space is symmetric if and only if the geodesic inversion preserves the set of horocycles.

The discovery of siRNAs as the mediators of RNA interference has led to an increasing interest in their therapeutic applications. Chemical modifications are introduced into siRNAs to optimize the potency, the stability and the pharmacokinetic properties in vivo. Here, we synthesize and test the effects of RNA-3′-PNA chimeras on siRNA functioning and stability. We demonstrate that the chemical modifications are compatible with the siRNA machinery, because all the PNA-modified siRNAs can efficiently mediate specific gene silencing in mammalian cells. Furthermore, we find that the modification on the sense strand of siRNA results in an increased persistence of the activity, whereas modification on both strands results in enhanced nuclease resistance in serum. © 2008 by MDPI.

Peptide nucleic acids (PNAs) are oligonucleotide mimics in which the sugar-phosphate backbone has been replaced by a pseudo-peptide backbone. Among PNA-based molecules, PNA-DNA conjugates characterized by tracts of DNA bound to N and/or C terminus of PNA are very soluble in aqueous media, are able to recognize exclusively single strands of DNA and RNA in antiparallel fashion, activate RNAse H, bind to transcription factors and are more stable than DNA to nucleases degradation. Very little information is available on chimeras constituted of alternating monomers of PNA and DNA. In this article, we describe a simple fully automated strategy for the synthesis of 6-mer and 10-mer alternate PNA-DNA chimeras consisting of polythymine oligomers, stability assays in fetal calf serum, UV and CD studies of the single strand alternate chimeras and of alternate chimera/DNA and alternate chimera/RNA duplexes. Evidences supporting the formation of duplex hybrids were found. Furthermore, the ability of forming Hoogsteen base pairing with duplex DNA was investigated. Finally, we tested the ability of the PNA-DNA alternates in (a) interfering with reverse transcription of eukaryotic mRNA and (b) inhibiting DNA-protein interactions. © 2007 Wiley Periodicals, Inc.

The structural characterization of a beta-cyclodextrin monosubstituted with the peptide cyclo(L-His-L-Leu) is reported. This work provides an x-ray example of a covalently bound group that folds in such a way that the terminal apolar side chain is retained in the hydrophobic interior of the cone-shaped cyclodextrin cavity. 6-Deoxy-6-cyclo(L-histidyl-L-leucyl)-beta-cyclodextrin crystallizes in the space group P1 with cell dimensions a = 14.728(8) A, b = 15.084(7) A, c = 18.182(10) A, alpha = 94.36(6) degrees, beta = 95.81(5) degrees, gamma = 116.08(9) degrees; overall isotropic agreement R = 10.6% for 5703 observed reflections (Fo greater than 3 sigma). The molecular structure consists of two independent molecules with the formula C54H86N4O36.7.25H2O. Each molecule assumes a "sleeping swan"-like overall shape with the hydrophobic leucine side chain inserted inside the cavity of the macrocycle. The two independent units give rise to a head-to-tail dimer linked by hydrogen bonds occurring between primary and secondary hydroxyl groups of the two monomers. The packing of the dimers produces cavities containing water molecules. There are infinite hydrophilic channels running in the crystal, which is similar to what is found in the structures of cyclic peptides.

We prove several Paley–Wiener-type theorems related to the spherical transform on the Gelfand pair $$\big ({H_n}\rtimes {\text {U}(n)},{\text {U}(n)}\big )$$(Hn⋊U(n),U(n)), where $${H_n}$$Hn is the $$2n+1$$2n+1-dimensional Heisenberg group. Adopting the standard realization of the Gelfand spectrum as the Heisenberg fan in $$\mathbb {R}^2$$R2, we prove that spherical transforms of $${\text {U}(n)}$$U(n)-invariant functions and distributions with compact support in $${H_n}$$Hn admit unique entire extensions to $$\mathbb {C}^2$$C2, and we find real-variable characterizations of such transforms. Next, we characterize the inverse spherical transforms of compactly supported functions and distributions on the fan, giving analogous characterizations.

Let N be an H-type group of homogeneous dimension e. We study the space of biradial Schwartz functions on N by means of the Gelfand transform. This enables us to characterize the class of biradial homogeneous distributions on N of degree alpha, with 0 less than or equal to alpha < Q, which are C-infinity away from the identity, via the Gelfand transform

The synthesis, solution NMR investigation and solid-state structural characterization of a new difunctionalized β-cyclodextrin (β-CD) are reported. 6I,6II-Dideoxy-6I,6II-bis[2-(2-pyridyl)ethylamino]-β-cyclomaltoheptaose is synthesized for the first time using a regioselective synthetic procedure. On the basis of an aqueous solution NMR investigation, the intramolecular interaction of the two pyridine rings with the upper rim of the cavity is proposed. 6I,6II-Dideoxy-6I,6II-bis[2-(2-pyridyl)ethylamino]-β-cyclomaltoheptaose, C56H86N4O33, crystallizes in the monoclinic P21 space group with cell dimension a = 26.303(5), b = 15.670(5), c = 8.276(2) A and β = 103.60(2)°, and 5.5 molecules of water for each independent β-cyclodextrin molecule. The structure refines to R = 0.103 for 2270 observed reflections [I ≥ 3σ(I)] and represents the first example of a complete structural characterization of a branched difunctionalized β-cyclodextrin. In the solid state, the macrocycle structure maintains an approximate seven-fold symmetry with only small changes occurring in the cyclic carbohydrate conformation where two consecutive primary hydroxy groups are substituted with bulky moieties. The two aminoethylpyridine groups linked to contiguous glucosidic units show different behaviour, with one group extending away from the cavity of the β-CD, the other remaining in the proximity of the ‘mouth’ of the cavity. However, in the crystal the aminoethylpyridine group extending away from the cavity of the β-CD is deeply inserted into the cavity of the adjacent β-CD molecule translated along the c axis, giving rise to long rows of β-CD molecules stabilized by these host–guest interactions. The resulting polymeric arrangement has already been observed in crystal structures of other monosubstituted β-CDs.

The terminally blocked tetrapeptide pBrBz-[D-(alpha Me)Leu]2-D-(alpha Me)Val-D-(alpha Me)Leu-OfBu is folded in the crystal state in a left-handed 3(10)-helical structure stabilized by two consecutive 1

The fully blocked pentapeptide Tfa‐(Deg)2‐L‐Abu‐(Deg)2‐OtBu (Tfa:triflouroacetyl; Deg: Cα,α‐diethylglycine; OtBu: tert‐butoxy) adopts in the crystal state a regular, right‐handed 310‐helical structure stabilized by three N  H … O  C intramolecular 1 ← 4 (or C10) H bonds, as determined by an x‐ray diffraction analysis. However, a Fourier transform ir absorption and 1H‐nmr study strongly supports the view that in deuterochloroform solution the four Deg residues at both termini of the peptide main chain are involved in successive, fully extended C5 forms. A comparison with the stable, fully developed, multiple C5 conformation of Tfa‐(Deg)5‐OtBu indicates that incorporation of an Abu guest residue, interrupting the side‐chain uniformity of the host (Deg)5 homopeptide, while altering only marginally the conformation in a solvent of low polarity, is responsible for a dramatic perturbation of the crystal‐state structure. © 1994 John Wiley & Sons, Inc. Copyright © 1994 John Wiley & Sons, Inc.

A survey of literature for the various types of helices experimentally observed in high-resolution single crystal x-ray diffraction analyses of peptides has allowed to determine accurate conformational and helical parameters for the various secondary structures such as the alpha-helix, the 3(10)-helix, the fully extended conformation (2(5)-helix) and the beta-bend ribbon spiral. For each of these structures the characteristic phi, psi conformational parameters, n, the number of residues per turn, h, the height per residues and p, the pitch of the helix are described.

The recent characterization of the prokaryotic Cys2His2 zinc-finger domain, identified in Ros protein from Agrobacterium tumefaciens, has demonstrated that, although possessing a similar zinc coordination sphere, this domain is structurally very different from its eukaryotic counterpart. A search in the databases has identified *300 homologues with a high sequence identity to the Ros protein, including the amino acids that form the extensive hydrophobic core in Ros. Surprisingly, the Cys2His2 zinc coordination sphere is generally poorly conserved in the Ros homologues, raising the question of whether the zinc ion is always preserved in these proteins. Here, we present a functional and structural study of a point mutant of Ros protein, Ros56–142C82D, in which the second coordinating cysteine is replaced by an aspartate, 5 previously-uncharacterized representative Ros homologues from Mesorhizobium loti, and 2 mutants of the homologues. Our results indicate that the prokaryotic zinc-finger domain, which in Ros protein tetrahedrally coordinates Zn(II) through the typical Cys2His2 coordination, in Ros homologues can either exploit a CysAspHis2 coordination sphere, previously never described in DNA binding zinc finger domains to our knowledge, or lose the metal, while still preserving the DNA-binding activity. We demonstrate that this class of prokaryotic zinc-finger domains is structurally very adaptable, and surprisingly single mutations can transform a zinc-binding domain into a nonzinc-binding domain and vice versa, without affecting the DNA-binding ability. In light of our findings an evolutionary link between the prokaryotic and eukaryotic zinc-finger domains, based on bacteria-to-eukaryota horizontal gene transfer, is discussed. The recent characterization of the prokaryotic Cys(2)His(2) zinc-finger domain, identified in Ros protein from Agrobacterium tumefaciens, has demonstrated that, although possessing a similar zinc coordination sphere, this domain is structurally very different from its eukaryotic counterpart. A search in the databases has identified approximate to 300 homologues with a high sequence identity to the Ros protein, including the amino acids that form the extensive hydrophobic core in Ros. Surprisingly, the Cys(2)His(2) zinc coordination sphere is generally poorly conserved in the Ros homologues, raising the question of whether the zinc ion is always preserved in these proteins. Here, we present a functional and structural study of a point mutant of Ros protein, Ros(56-142)C82D, in which the second coordinating cysteine is replaced by an aspartate, 5 previously-uncharacterized representative Ros homologues from Mesorhizobium loti, and 2 mutants of the homologues. Our results indicate that the prokaryotic zinc-finger domain, which in Ros protein tetrahedrally coordinates Zn(II) through the typical Cys(2)His(2) coordination, in Ros homologues can either exploit a CysAspHis(2) coordination sphere, previously never described in DNA binding zinc finger domains to our knowledge, or lose the metal, while still preserving the DNA-binding activity. We demonstrate that this class of prokaryotic zinc-finger domains is structurally very adaptable, and surprisingly single mutations can transform a zinc-binding domain into a nonzinc-binding domain and vice versa, without affecting the DNA-binding ability. In light of our findings an evolutionary link between the prokaryotic and eukaryotic zinc-finger domains, based on bacteria-to-eukaryota horizontal gene transfer, is discussed.

The first putative prokaryotic Cys2His2 zinc-finger domain has been identified in the transcriptional regulator Ros from Agrobacterium tumefaciens, indicating that the Cys2His2 zinc-finger domain, originally thought to be confined to the eukaryotic kingdom, could be widespread throughout the living kingdom from eukaryotic, both animal and plant, to prokaryotic. In this article we report the NMR solution structure of Ros DNA-binding domain (Ros87), providing 79 structural characterization of a prokaryotic Cys2His2 zinc-finger domain. The NMR structure of Ros87 shows that the putative prokaryotic Cys2His2 zinc-finger sequence is indeed part of a significantly larger zinc-binding globular domain that possesses a novel protein fold very different from the classical fold reported for the eukaryotic classical zinc-finger. The Ros87 globular domain consists of 58 aa (residues 9–66), is arranged in a beta beta beta alpha alpha topology, and is stabilized by an extensive 15-residue hydrophobic core. A backbone dynamics study of Ros87, based on 15N R1, 15N R2, and heteronuclear 15N-{1H}-NOE measurements, has further confirmed that the globular domain is uniformly rigid and flanked by two flexible tails. Mapping of the amino acids necessary for the DNA binding onto Ros87 structure reveals the protein surface involved in the DNA recognition mechanism of this new zinc-binding protein domain. The first putative prokaryotic Cys(2)His(2) zinc-finger domain has been identified in the transcriptional regulator Ros from Agrobacterium tumefaciens, indicating that the Cys(2)His(2) zinc-finger domain, originally thought to be confined to the eukaryotic kingdom, could be widespread throughout the living kingdom from eukaryotic, both animal and plant, to prokaryotic. In this article we report the NMR solution structure of Ros DNA-binding domain (Ros87), providing 79 structural characterization of a prokaryotic Cys(2)His(2) zinc-finger domain. The NMR structure of Ros87 shows that the putative prokaryotic Cys(2)His(2) zinc-finger sequence is indeed part of a significantly larger zinc-binding globular domain that possesses a novel protein fold very different from the classical fold reported for the eukaryotic classical zinc-finger. The Ros87 globular domain consists of 58 aa (residues 9-66), is arranged in a beta beta beta alpha alpha topology, and is stabilized by an extensive 15-residue hydrophobic core. A backbone dynamics study of Ros87, based on N-15 R-1, N-15 R-2, and heteronuclear N-15-{H-1}-NOE measurements, has further confirmed that the globular domain is uniformly rigid and flanked by two flexible tails. Mapping of the amino acids necessary for the DNA binding onto Ros87 structure reveals the protein surface involved in the DNA recognition mechanism of this new zinc-binding protein domain.

Transcriptional factors bearing a Cys2His2 zinc finger were thought to be confined to eukaryotes, but recent studies have suggested their presence also in prokaryotes. In this paper, we report the first complete functional characterization of the DNA binding domain present in the putative Cys2His2 zinc finger-containing prokaryotic transcriptional regulator Ros from Agrobacterium tumefaciens. We demonstrate that in the single zinc binding motif present in the Ros protein the metal ion is coordinated by two cysteines (Cys79 and Cys82) and two histidines (His92 and His97), separated by a shorter spacer with respect to the eukaryotic classical Cys2His2 domains. The Cys2His2 zinc finger motif is essential for Ros DNA binding and is part of a larger DNA binding domain which includes four basic regions located on either side of the finger, one at the N-terminus and three at the C-terminus. The one described here is a novel type of DNA binding domain containing a noncanonical Cys 2His2 zinc finger motif which, by sequence alignment, seems to be conserved in all the bacterial putative zinc finger proteins identified so far. Interestingly, basic amino acids have been shown to be important in stabilizing the DNA binding of eukaryotic single Cys 2His2 zinc finger domains, confirming that the modality of DNA binding using a single zinc finger motif flanked by basic residues is widespread throughout the living kingdom from eukaryotic, both animal and plant, to prokaryotic, even if in each kingdom it presents its peculiarity. © 2006 American Chemical Society.

The generalised Cayley transform C \mathcal {C} from an Iwasawa N N -group into the corresponding real unit sphere S \mathbb {S} induces isomorphisms between suitable Sobolev spaces H α ( S ) \mathcal {H}^\alpha (\mathbb {S}) and H α ( N ) \mathcal {H}^\alpha (N) . We study the differential of C \mathcal {C} , and we obtain a criterion for a function to be in H α ( S ) \mathcal {H}^\alpha (\mathbb {S}) .

BACKGROUND The current study was designed to assess the activity and safety of a novel combination therapy for patients with recurrent or refractory aggressive non-Hodgkin lymphoma (NHL). METHODS Forty-three consecutive patients with recurrent or refractory aggressive NHL were treated with lomustine (chloroethylnitrosourea [CCNU]; 60 mg/m2 on Day 1), ifosfamide (1.5 g/m2 on Days 1, 2 and 21, 22), bleomycin (5 mg/m2 on Days 1, 5 and 21, 25), vincristine (1.4 mg/m2 on Days 1, 8 and 21, 28), and cisplatin (25 mg/m2 on Days 3, 4, 5 and 23, 24, 25), every 42 days (CIBO-P regimen). RESULTS Thirty-nine patients (91%) were evaluable for response. The median patient age was 63 years. Thirty-five percent of the patients had received ≥ 2 lines of previous chemotherapy and 40% had elevated lactate dehydrogenase levels at the time of treatment initiation. The overall objective response rate was 77% (95% confidence interval [95% CI], 63–90%), including 19 (49%) complete (CR) and 11 (28%) partial responses. CIBO-P induced responses in primary refractory disease and in patients treated for second or subsequent disease recurrences. A CR with previous therapy was the most important factor associated with a significantly higher CR rate. The median duration of response was 6 months (95% CI, 4.4–7.7 months) and the median survival duration was 10.7 months (95% CI, 5.9–18.1 months). Five patients (11.6%) remained disease free for ≥ 24 months. By multivariate analysis, a CR with previous therapy and average dose intensity of CIBO-P drugs were independent prognostic factors for time-to-treatment failure, whereas a CR with previous therapy and serum lactate dehydrogenase were independent predictors for survival. Myelosuppression was the most frequent serious complication of this regimen. However, none of the patients had hemorrhage with thrombocytopenia, and only 2 patients (5%) had febrile neutropenia. CONCLUSIONS In the current study, CIBO-P was a novel, highly active, and safe combination therapy for patients with refractory disease with a poor prognosis or for patients with multiply recurrent aggressive NHL. Cancer 2005. © 2005 American Cancer Society.

Oxidative addition reactions of Pd(PPh3)4 on the pyrimidine nucleosides 3′,5′-di-O-acetylthymidine and 3′,5′-di-O-acetyl-4-chlorothymidine and on the nucleobase 1-methylthymine have been investigated. N3 and C4 metal coordinated complexes 3 and 7 were isolated and characterized by spectroscopic techniques. Moreover, the crystal structur of the trans-[PdCl(1-methyl thymine)(PPh3) 2]·H2O (4) is reported. © 2005 American Chemical Society.

Let σ be the geodesic inversion on a Heisenberg type group N with homogeneous dimension Q, and denote by S the jacobian of σ. We prove that, for $ - \frac{1}{2}Q< \alpha< \frac{1}{2}Q$ , the operators $T_\alpha :f \mapsto S^{1/2 - \alpha /Q} (f \circ \sigma )$ are bounded on certain homogeneous Sobolev spaces $\mathcal{H}^\alpha (N)$ if and only if N is an Iwasawa N-group.

Zinc finger domains of the classical type represent the most abundant DNA binding domains in eukaryotic transcription factors. Plant proteins contain from one to four zinc finger domains, which are characterized by high conservation of the sequence QALGGH, shown to be critical for DNA-binding activity. The Arabidopsis thaliana SUPERMAN protein, which contains a single QALGGH zinc finger, is necessary for proper spatial development of reproductive floral tissues and has been shown to specifically bind to DNA. Here, we report the synthesis and UV and NMR spectroscopic structural characterization of a 37 amino acid SUPERMAN region complexed to a Zn(2+) ion (Zn-SUP37) and present the first high-resolution structure of a classical zinc finger domain from a plant protein. The NMR structure of the SUPERMAN zinc finger domain consists of a very well-defined betabetaalpha motif, typical of all other Cys(2)-His(2) zinc fingers structurally characterized. As a consequence, the highly conserved QALGGH sequence is located at the N terminus of the alpha helix. This region of the domain of animal zinc finger proteins consists of hypervariable residues that are responsible for recognizing the DNA bases. Therefore, we propose a peculiar DNA recognition code for the QALGGH zinc finger domain that includes all or some of the amino acid residues at positions -1, 2, and 3 (numbered relative to the N terminus of the helix) and possibly others at the C-terminal end of the recognition helix. This study further confirms that the zinc finger domain, though very simple, is an extremely versatile DNA binding motif.

The conformational features of human melanin-concentrating hormone (hMCH) [Asp1-Phe2-Asp3-Met4-Leu5-Arg6-cyclo(S[bond]S)(Cys7-Met8-Leu9-Gly10-Arg11-Val12-Tyr13-Arg14-Pro15-Cys16)-Trp17-Gln18-Val19], in water and in a CD(3)CN/H(2)O (1:1 v/v) mixture at 298 K, have been determined by NMR spectroscopy followed by simulated annealing and molecular dynamics analyses to identify conformer populations. Backbone clustering analysis of NMR-spectroscopy-derived structures in the 7-16 peptide region led to the identification of a single representative structure in each solvent. Both root mean square deviation clustering and secondary structure analysis of the final conformers in both solvents show substantial convergence of most conformers into a single fold in the 4-17 region, with a limited variability around Gly10 and Tyr13 on going from CD(3)CN/H(2)O to pure water. The main feature deduced from the analysis of secondary structures is the occurrence of an N-terminal alpha helix of variable length, which spans an overall residue range of 2-9. A comparative analysis in the two solvents highlights that these structures are substantially different from that reported in the literature for the cyclic MCH(5-14) subunit of salmon MCH, which was used to perform a molecular characterization of the MCH/receptor complex. Our conformational data call for a critical revision of the proposed MCH/receptor complex model.

Given a group N of Heisenberg type, we consider a one-dimensional solvable extension NA of N, equipped with the natural left-invariant Riemannian metric, which makes NA a harmonic (not necessarily symmetric) manifold. We define a Fourier transform for compactly supported smooth functions on NA, which, when NA is a symmetric space of rank one, reduces to the Helgason Fourier transform. The corresponding inversion formula and Plancherel Theorem are obtained. For radial functions, the Fourier transform reduces to the spherical transform considered by E. Damek and F. Ricci.

Let n = v + z be an H-type group, and let n + a be the harmonic semidirect product of n with a similar or equal to R. Let N A be the corresponding simply connected Lie group. If dim v = m and dim z = k, denote Q = m/2 + k. We prove that the spherical Fourier transform is a topological isomorphism between the p-Schwartz space L(p)(N A)(#), (0 < p less than or equal to 2), and the space of holomorphic rapidly decreasing functions on the strip {s is an element of C:\Re(s)\ < epsilon Q/2} with epsilon = 2/p - 1

The solid state conformational analysis of [Tyr4] cyclolinopeptide A has been carried out by x‐ray diffraction studies. The crystal structure of the monoclinic form, grown from a dioxane‐water mixture [a = 9.849 (5) Å, b = 20.752 (4) Å, c = 16.728 (5) Å, β = 98.83 (3)°, space group P21, Z = 2], shows the presence of five intramolecular N‐H OC hydrogen bonds, with formation of one C17 ring structure, one α‐turn (C13), one inverse γ‐turn (C7), and two β‐turns (C10, one of type III and one of type 1). The Pro1‐Pro2 peptide unit is cis (ω = 5°) all others are trans. The structure is almost superimposable with that of cyclolinopeptide A. The rms deviation for the atoms of the backbones is on the average 0.33 Å. © 1995 John Wiley & Sons, Inc. Copyright © 1995 John Wiley & Sons, Inc.

In the present paper we describe the synthesis, purification, single crystal x-ray analysis, and solution structural characterization by nmr spectroscopy, combined with restrained molecular dynamic simulations, of the cyclic hexapeptide cyclo-(Pro-Phe-beta-Ala-Phe-Phe-beta-Ala). The peptide was synthesized by classical solution methods and the cyclization of the free hexapeptide was accomplished in good yields in diluted methylenechloride solution using N,N-dicyclohexyl-carbodiimide. The compound crystallizes in the monoclinic space group P2(1) from methanol/ethyl acetate. The molecule adopts in the solid state a conformation characterized by cis beta-Ala6-Pro1 peptide bond. The alpha-amino acid residues are at the corner positions of turned structures. The Pro1-Phe2 segment is incorporated in a pseudo type I beta-turn, while Phe4-Phe5 is in a typical type I beta-turn. Assignment of all 1H and 13C resonances was achieved by homo- and heteronuclear two-dimensional techniques in dimethylsulfoxide (DMSO) solutions. The conformational analysis was based on interproton distances derived from rotating frame nuclear Overhauser effect spectroscopy spectra and homonuclear coupling constants. Restrained molecular dynamic simulation in vacuo was also performed to built refined molecular models. The molecule is present in DMSO solution as two slowly interconverting conformers, characterized by a cis-trans isomerism around the beta-Ala6-Pro1 peptide bond. This work confirms our expectations on the low propensity of beta-alanyl residues to be positioned at the corners of turned structure.

In the present paper we describe the synthesis, purification, single crystal x‐ray analysis, and solution structural characterization by nmr spectroscopy, combined with restrained molecular dynamic simulations, of the cyclic hexapeptide cyclo‐(Pro‐Phe‐β‐Ala‐Phe‐Phe‐β‐Ala). The peptide was synthesized by classical solution methods and the cyclization of the free hexapeptide was accomplished in good yields in diluted methylenechloride solution using N, N‐dicyclohexyl‐carbodiimide. The compound crystallizes in the monoclinic space group P21 from methanol/ethyl acetate. The molecule adopts in the solid state a conformation characterized by cis β‐Ala6‐Pro1 peptide bond. The α‐amino acid residues are at the corner positions of turned structures. The Pro1‐Phe2 segment is incorporated in a pseudo type I β‐turn, while Phe4‐Phe5 is in a typical type I β‐turn. Assignment of all 1H and 13C resonances was achieved by homo‐ and heteronuclear two‐dimensional techniques in dimethylsulfoxide (DMSO) solutions. The conformational analysis was based on inter‐proton distances derived from rotating frame nuclear Overhauser effect spectroscopy spectra and homonuclear coupling constants. Restrained molecular dynamic simulation in vacuo was also performed to built refined molecular models. The molecule is present in DMSO solution as two slowly interconverting conformers, characterized by a cis‐tran isomerism around the β‐Ala6‐Pro1 peptide bond. This work confirms our expectations on the low propensity of β‐alanyl residues to be positioned at the corners of turned structure. © 1994 John Wiley & Sons, Inc. Copyright © 1994 John Wiley & Sons, Inc.

The x-ray diffraction analyses of three N- and C-terminally blocked L, D dipeptides, namely t-Boc-D-Leu-L-Leu-OMe (1), t-Boc-L-Ile-D-alle-OMe (2), and t-Boc-D-aIle-L-Ile-OMe (3) containing enantiomeric or diastereomeric amino acid residues have been carried out. The structures were determined by direct methods and refined anisotropically to final R factors of 0.077. 0.058. and 0.072 for (1) (2) and (3), respectively. Peptides 1–3 all assume a similar U-shaped structure with ϕ and ψ torsion angles cosrresponding to one of the possible calculated minimum energy regions (regions E and G for L residues, and F*. D* and H* for D residues). The peptide backbones of 1-3 are almost super-imposable [provided that the appropriate inversion of the chiral centers of (2) is made]. Side-chain conformations of Leu residues in peptide (1) are g− (tg−) for the L-Leu residue and the mirrored g+ (tg+) for the D-Leu residue; however, in peptides (2) and (3) the conformations of the isoconfiguralional side chains of the Ile or allo-Ile residues are (g−t) t and (tg+) tfor the L-Ile and the D-allo-Ile moieties, respectively. In all cases, these conformations correspond to the more populated conformers of β-branched residues statistically found in crystal structures of small peptides. The results seem to indicate that, at least in short peptides with enantiomeric or diastereoisomeric residues, the change in chirality in the main-chain atoms perturbs the backbone conformation to a lesser extent and the side chain conformation to a greater extent. © 1995 John Wiley & Sons, Inc.

A single‐crystal x‐ray diffraction analysis of Boc‐L‐Ala‐D‐aIle‐L‐Ile‐OMe has been carried out. The analysis has shown (a) that the tripeptide molecules have in part an α‐extended conformation, the torsion angles of the L‐Ala and D‐aIle residues being φ1 = −75.1° and ψ1 = −25.8° and φ2 = 67.3° and ψ2 = 44.1°, respectively, and (b) that the molecules are organized in rippled planes where they occur in relative antiparallel orientation linked together side by side by H bonds. This molecular organization of the tripeptide corresponds closely to that of an antiparallel α‐pleated sheet, and likely constitutes the first example of a structure of this kind for which a characterization at the atomic level has been achieved. A molecular dynamics study has shown that the molecular conformation of the tripeptide in the crystalline state is determined primarily by intermolecular interactions. © 1994 John Wiley & Sons, Inc. Copyright © 1994 John Wiley & Sons, Inc.