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The interpretation of molecular translational diffusion as measured by pulsed gradient spin-echo NMR (PGSE NMR) can be complicated by the presence of chemical exchange and/or dipolar cross-relaxation (including relayed cross-relaxation via spin diffusion). The magnitude of influence depends on the kinetics of exchange and/or dipolar cross-relaxation present within the system as well as the PGSE NMR sequences chosen for measurements. First, we present an exchange induced zero-crossing phenomenon for signal attenuation of water in lipidic cubic phases (formed by a mixture of monoolein and water) in the presence of pulsed gradients observed using a standard STimulated Echo (STE) sequence. This magnetization exchange induced zero-crossing phenomenon, a pseudo-negative diffraction-like feature, resembles that reported previously for restricted diffusion when locally anisotropic pores are polydisperse or randomly oriented. We then demonstrate the elimination of these exchange and/or dipolar cross-relaxation induced effects with the use of a chemical shift selective STE (CHESS-STE) sequence, adapted from the previously reported band-selective short transient STE sequence, along with results obtained from the bipolar pulse pair STE sequence for comparison. The CHESS-STE sequence introduced here represents a generic form of PGSE NMR sequences for obtaining water diffusion coefficients free from the influence of exchange and/or dipolar cross-relaxation in complex systems. It has potential applications in measuring translational diffusion of water in biopolymer mixtures as well as probing the microscopic structure in materials via water restricted diffusion measured by PGSE NMR, particularly when the potential presence of exchange/cross-relaxation is of concern. [ABSTRACT FROM AUTHOR]

The opportunistic pathogen Pseudomonas aeruginosa produces multifunctional, polar, filamentous appendages termed type IV pill. Type IV pill are involved in colonization during infection, twitching motility, biofilm formation, bacteriophage infection, and natural transformation. Electrostatic surface analysis of modeled pilus fibers generated from P. aeruginosa strain PAK, K122-4, and KB-7 pilin monomers suggested that a solvent-exposed band of positive charge may be a common feature of all type IV pili. Several functions of type IV pili, including natural transformation and biofilm formation, involve DNA. We investigated the ability of P. aeruginosa type IV pili to bind DNA. Purified PAK, K122-4, and KB-7 pili were observed to bind both bacterial plasmid and salmon sperm DNA in a concentration-dependent and saturable manner. PAK pili had the highest affinity for DNA, followed by K122-4 and KB-7 pili. DNA binding involved backbone interactions and preferential binding to pyrimidine residues even though there was no evidence of sequence-specific binding. Pilusmediated DNA binding was a function of the intact pilus and thus required elements present in the quaternary structure. However, binding also involved the pilus tip as tip-specific, but not base-specific, antibodies inhibited DNA binding. The conservation of a Thr residue in all type IV pilin monomers examined to date, along with the electrostatic data, implies that DNA binding is a conserved function of type IV pili. Pilus-mediated DNA binding could be important for biofilm formation both in vivo during an infection and ex vivo on abiotic surfaces.

Research has been conducted on the CXCR3 binding chemokines, IP-10 (CXCL10). The IP-10 surface interacting with CXCR3 N-terminus has been identified via monitoring the changes in its NMR spectrum after the addition of CXCR3 N-terminal peptide and the details are presented.

Results show that the rigid backbone scaffold of the bacterial K122-4 pilin aids in host cell receptor attachment preserving conformation of the antibody recognizing epitope as shown by (sup)15N NMR relaxation techniques.

Research has been conducted on the CC chemokine I-309. The use of (super)1 H nuclear magnetic resonance spectroscopy in investigating the three-dimensional solution structure of I-309 is described.

Ligand competition with a number of chromophoric probes were used to determine the binding affinities for [Zn.sup.II] and [Cu.sup.I] of each metal-binding domain (MBD). The obtained information highlighted the potential toxicity of [Cu.sup.+] in vivo and more sensitive magnitude of copper sensor proteins compared to zinc sensor proteins.

The results from (super 15)N relaxation measurements carried out in both the laboratory and frames for the insulin-like growth factors binding proteins (IGFBPs) are presented. The results strongly suggest possible conformation switching or population shifting between pre-existing conformations in C-terminal domain of IGFBP-6 upon binding to insulin-like growth factors (IGF)-II.

Research has been conducted on phage-display peptides which bind to apical membrane antigen 1 and inhibit erythrocytes' parasite invasion. The authors describe their study of the solution structures of these peptides, and the biological structures and properties of the analogues based of the most active peptide.

Pulsed-field gradient nuclear magnetic resonance has seen an increase in applications spanning a broad range of disciplines where molecular translational diffusion properties are of interest. The current study introduces and experimentally evaluates the measurement of translational diffusion coefficients of 15N-enriched biomolecules using a 1H-15N HMQC-filtered band-selective excitation short transient (BEST) sequence as an alternative to the previously described SOFAST-XSTE sequence. The results demonstrate that accurate translational diffusion coefficients of 15N-labelled peptides and proteins can be obtained using this alternative 1H-15N HMQC-filtered BEST sequence which is implementable on NMR spectrometers equipped with probes fitted with a single-axis field gradient, including most cryoprobes dedicated to bio-NMR. The sequence is of potential use for direct quantification of protein or peptide translational diffusion within complex systems, such as in mixtures of macromolecules, crowded solutions, membrane-mimicking media and in bicontinuous cubic phases, where conventional sequences may not be readily applicable due to the presence of intense signals arising from sources other than the protein or peptide under investigation. [ABSTRACT FROM AUTHOR]