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Despite many recent studies of G-protein-coupled receptor (GPCR) structures, it is not yet well understood how these receptors activate G proteins. The GPCR assay using baker's yeast, Saccharomyces cerevisiae, is an effective experimental model for the characterization of GPCR-Gα interactions. Here, using the yeast endogenous Gα protein (Gpa1p) as template, we constructed various chimeric Gα proteins with a region that is considered to be necessary for interaction with mammalian receptors. The signaling assay using the yeast pheromone receptor revealed that the chimeric Gα protein harboring 37 gustducin-specific amino acid residues at its C-terminus (GPA1/gust37) maintained functionality in yeast. In contrast, GPA1/gust44, a variant routinely used in mammalian experimental systems, was not functional.

D,L-threo-beta-Benzyloxyaspartate (D,L-TBOA), an analog of threo-beta-hydroxyaspartate (THA) possessing a bulky substituent, is a potent non-transportable blocker for the excitatory amino acid transporters, EAAT1, 2 and 3, while L-threo-beta-methoxyaspartate (L-TMOA) is a blocker for EAAT2, but a substrate for EAAT1 and EAAT3. To characterize the actions of these THA analogs and the function of EAAT4 and EAAT5, we performed electrophysiological analyses in EAAT4 or EAAT5 expressed on Xenopus oocytes. In EAAT4-expressing oocytes, D,L-TBOA acted as a non-transportable blocker, while L-TMOA like D,L-THA was a competitive substrate. In contrast, D,L-THA, D,L-TBOA and L-TMOA all strongly attenuated the glutamate-induced currents generated by EAAT5. Among them, L-TMOA showed the most potent inhibitory action. Moreover, D,L-THA, D,L-TBOA and L-TMOA themselves elicited outward currents at negative potentials and remained inward at positive potentials suggesting that D,L-TBOA and L-TMOA, as well as D,L-THA, not only act as non-transportable blockers, but also block the EAAT5 leak currents. These results indicate that EAATs 4 and 5 show different sensitivities to THA analogs although they share properties of a glutamate-gated chloride channel.

Na 1 -dependent excitatory amino acid transporters (EAATs) normally function to remove extracellular glutamate from brain extracellular space, but EAATs can also increase extracellular glutamate by reversal of uptake. Effects of inhibitors on EAATs can be complex, depending on cell type, whether conditions favor glutamate uptake or uptake reversal and whether the inhibitor itself is a substrate for the transporters. The present study assessed EAAT inhibitors for their ability to inhibit glutamate uptake, act as transporter substrates and block uptake reversal in astrocyte and neuron cultures. L-threo-bhydroxyaspartate (L-TBHA), DL-threo-b-benzyloxyaspartate (DL-TBOA), L-trans-pyrrolidine-2,4-dicarboxylic acid (L-trans2,4-PDC) (1/‐)-cis-4-methy-trans-pyrrolidine-2,4-dicarboxylic acid (cis-4-methy-trans-2,4-PDC) and L-antiendo-3,4-methanopyrrolidine-2,4-dicarboxylic acid (L-antiendo-3,4-MPDC) inhibited L-[ 14 C]glutamate uptake in astrocytes with equilibrium binding constants ranging from 17 mM (DL-TBOA and L-TBHA) ‐4 3mM (cis-4-methy-trans-2,4-PDC). Transportability of inhibitors was assessed in astrocytes and neurons. While L-TBHA, L-trans-2,4-PDC, cis-4-methy-trans-2,4-PDC and L-antiendo3,4-MPDC displayed significant transporter substrate activities in neurons and astrocytes, DL-TBOA was a substrate only in astrocytes. This effect of DL-TBOA was concentrationdependent, leading to complex effects on glutamate uptake reversal. At concentrations low enough to produce minimal DL-TBOA uptake velocity (# 10 mM), DL-TBOA blocked uptake reversal in ATP-depleted astrocytes; this blockade was negated at concentrations that drove substantial DL-TBOA uptake (. 10 mM). These findings indicate that the net effects of EAAT inhibitors can vary with cell type and exposure

DL-threo-beta-benzyloxyaspartate (DL-TBOA) is a non-transportable blocker of the glutamate transporters that serves as an indispensable tool for the investigation of the physiological roles of the transporters. To examine the precise interaction between a blocker and the transporters, we synthesized the optically pure isomers (L- and D-TBOA) and its erythro-isomers. L-TBOA is the most potent blocker for the human excitatory amino acid transporters (EAAT1-3), while D-TBOA revealed a difference in the pharmacophores between EAAT1 and EAAT3. We also synthesized the substituent variants (methyl or naphthylmethyl derivatives) of L-TBOA. The results obtained here suggest that bulky substituents are crucial for non-transportable blockers.

DL-threo-beta-Benzyloxyaspartate (DL-TBOA), a novel derivative of DL-threo-beta-hydroxyaspartate, was synthesized and examined as an inhibitor of sodium-dependent glutamate/aspartate (excitatory amino acid) transporters. DL-TBOA inhibited the uptake of [14C]glutamate in COS-1 cells expressing the human excitatory amino acid transporter-1 (EAAT1) (Ki = 42 microM) with almost the same potency as DL-threo-beta-hydroxyaspartate (Ki = 58 microM). With regard to the human excitatory amino acid transporter-2 (EAAT2), the inhibitory effect of DL-TBOA (Ki = 5.7 microM) was much more potent than that of dihydrokainate (Ki = 79 microM), which is well known as a selective blocker of this subtype. Electrophysiologically, DL-TBOA induced no detectable inward currents in Xenopus laevis oocytes expressing human EAAT1 or EAAT2. However, it significantly reduced the glutamate-induced currents, indicating the prevention of transport. The dose-response curve of glutamate was shifted by adding DL-TBOA without a significant change in the maximum current. The Kb values for human EAAT1 and EAAT2 expressed in X. laevis oocytes were 9.0 microM and 116 nM, respectively. These results demonstrated that DL-TBOA is, so far, the most potent competitive blocker of glutamate transporters. DL-TBOA did not show any significant effects on either the ionotropic or metabotropic glutamate receptors. Moreover, DL-TBOA is chemically much more stable than its benzoyl analog, a previously reported blocker of excitatory amino acid transporters; therefore, DL-TBOA should be a useful tool for investigating the physiological roles of transporters.

Four subtypes of excitatory amino acid transporters (EAAT1-4) have been identified in the mammalian brain. A number of pharmacological agents have been developed to study their intrinsic properties and function. Up to now, blockers were available only for EAAT2, whereas all the inhibitors of glutamate uptake active on the other subtypes were proved to be substrates of the transporters. We synthesized five new derivatives of DL-threo-beta-hydroxyaspartic acid, a well known general substrate of EAATs, and investigated their potential blocking activity on the cloned bovine EAAT1 expressed in the Xenopus oocyte system, by using radiotracer and voltage-clamp techniques. Two of our derivatives proved to be substrates for bovine EAAT1, with reduced electrogenicity compared with their parent compound, and an affinity of 40 and 64 microM. The last three derivatives displayed a blocking activity on bovine EAAT1. The affinity of DL-threo-beta-benzoyloxyaspartate and DL-threo-beta-(1-naphthoyl)oxyaspartate was determined by Schild analysis as 17.2 and 52.1 microM, respectively. These blockers should help in the better understanding of the key intrinsic properties of EAAT1. Moreover, they appear as good candidates for a general blocking activity on EAATs.

1. An SCP-related peptide, Ala-Pro-Asn-Phe-Leu-Ala-Tyr-Pro-Arg-Leu-NH2, was isolated from the ABRMs of Mytilus edulis. The peptide was designated Mytilus SCP. 2. At 10(-10) M or higher, Mytilus SCP showed a potentiating effect on phasic contraction of the ABRM in response to repetitive electrical stimulation. In contrast, the peptide did not show any potentiating effect on contractures in response to ACh and the FMRFamide-related Mytilus decapeptide, suggesting that the potentiating effect on phasic contraction was brought about by an action of the peptide on the nerve elements in the ABRM. 3. At 10(-8) M or higher, Mytilus SCP showed a catch-relaxing effect in addition to the potentiating effect. The relaxing effect was blocked by mersalyl, suggesting that it was also brought about by a presynaptic action. 4. Various analogues of Mytilus SCP were examined on the ABRM. Leu-Ala-Tyr-Pro-Arg-Leu-NH2 was suggested to be the minimum structure required for both potentiating and relaxing activities on the ABRM. Leu-D-Ala-Tyr-Pro-Arg-D-Leu-NH2 and D-Leu-Ala-Tyr-Pro-Arg-D-Leu-NH2 were found to show strong potentiating and relaxing activities, though they were less potent than the Mytilus SCP.

1. An FMRFamide-related decapeptide isolated from the anterior byssus retractor muscle (ABRM) of the bivalve mollusc, Mytilus edulis, was shown to have D-Leu as the second amino acid residue. 2. The excitatory effects of the peptide (Mytilus-FFRFamide) on the ABRM were not changed appreciably by substituting an L-Leu residue for the D-Leu residue.

A novel pentapeptide containing a D-amino acid residue was purified from the central ganglia of the African giant snail Achatina fulica Ferussac, and it was named fulicin. The primary structure of the peptide was determined to be Phe- d -Asn-Glu-Phe-Val-NH2. Fulicin potentiated tetanic contraction of the penis retractor muscle of this snail at very low concentrations, and also showed modulatory actions on the activity of the buccal and ventricular muscles and the central ganglionic neurons.

Achatin-I previously purified from the ganglia of the African giant snail Achatina fulica was isolated from the atria of this snail. Achatin-I appeared to enhance the cardiac activity in two ways; centrally this peptide increased impulse frequency and produced spike broadening of the identified heart excitatory neuron, PON, and peripherally it enhanced amplitude and frequency of the heart beat. Achatin-I showed excitatory actions not only on the heart but on several other muscles.

L-Glutamate is the major excitatory neurotransmitter in the mammalian central nervous system. Termination of glutamate receptor activation and maintenance of low extracellular glutamate concentrations are primarily achieved by glutamate transporters (excitatory amino acid transporters 1-5, EAATs1-5) located on both the nerve endings and the surrounding glial cells. To identify the physiological roles of each subtype, subtype-selective EAAT ligands are required. In this study, we developed a binding assay system to characterize EAAT ligands for all EAAT subtypes. We recently synthesized novel analogs of threo-beta-benzyloxyaspartate (TBOA) and reported that they blocked glutamate uptake by EAATs 1-5 much more potently than TBOA. The strong inhibitory activity of the TBOA analogs suggested that they would be suitable to use as radioisotope-labeled ligands, and we therefore synthesized a tritiated derivative of (2S,3S)-3-{3-[4-ethylbenzoylamino]benzyloxy}aspartate ([3H]ETB-TBOA). [3H]ETB-TBOA showed significant high-affinity specific binding to EAAT-transfected COS-1 cell membranes with each EAAT subtype. The Hill coefficient for the Na+-dependence of [3H]ETB-TBOA binding revealed a single class of noncooperative binding sites for Na+, suggesting that Na+ binding in the ligand binding step is different from Na+ binding in the substrate uptake process. The binding was displaced by known substrates and blockers. The rank order of inhibition by these compounds was consistent with glutamate uptake assay results reported previously. Thus, the [3H]ETB-TBOA binding assay will be useful to screen novel EAAT ligands for all EAAT subtypes.

The olfactory system plays important roles in various crustacean behaviors. Despite numerous studies on different aspects of the olfactory neural pathway, only the decapod-tachykinin-related peptide (decapod-TRP) has been identified as a neuromodulator in this processing to date. To establish the functions of other related neuropeptides, we initially performed cDNA cloning of FMRFamide-related peptide (FaRP) and allatostatin (AST)-like peptide from the crayfish Procambarus clarkii, followed by in situ hybridization (ISH) analysis of these peptides, along with decapod-TRP, orcokinin, and crustacean-SIFamide. Cloned FaRP cDNA encodes seven copies of C-terminal RN(F/Y)LRFamide-containing peptide, whereas AST-like peptide cDNA comprises 29 copies of AST-like peptide (–YXFGLamide) and three additional putative peptides. ISH analysis of the brain revealed specific expression of crustacean-SIFamide mRNA in most projection neurons (cell cluster 10), and predominant localization of other mRNAs to interneurons. The data suggest that the crustacean-SIFamide neuropeptide is involved in output of the deutocerebrum to the protocerebrum. Double-fluorescence ISH data further disclose that, in cluster 9, orcokinin is coexpressed in decapod-TRP-specific interneurons, whereas AST-like peptide-containing cells do not overlap with orcokinin-expressing cells. On the other hand, FaRP-expressing cells overlap with both orcokinin- and AST-like peptide-specific cells. In cluster 11, where signals for AST-like peptide are absent, a number of interneurons express both decapod-TRP and orcokinin, emphasizing a close relationship between these two factors with regard to olfactory processing, and possibly tactile and/or visual sensory systems. These characteristic expression patterns of neuropeptides support their distinct involvement in the modulation of olfactory processing. J. Comp. Neurol. 496:135–147, 2006. © 2006 Wiley-Liss, Inc.

We report here the identification of a tachykinin-related peptide (TRP) in crustaceans. Direct MALDI-TOF MS with brain slices of the crayfish Procambarus clarkii indicated the presence of a peptide having an MS number of around 934. Quadrupole orthogonal acceleration time-of-flight (Q-TOF) MS/MS analysis implied the sequence to be APSGFLGMRamide, identical to that of CabTRP Ia, isolated previously from the crab Cancer borealis, and Pev-tachykinin, from the shrimp Penaeus vannamei. The peptide has been shown to be myoactive in the cockroach hindgut, but the structure of its precursor protein had not been elucidated. A cDNA encoding crayfish preproTRP was cloned, revealing that the 225-residue protein contains seven identical copies of the peptide APSGFLGMRamide. This is unique because TRPs identified in other invertebrates were known to exist in several related forms in each species. The conserved structure of TRP in crustaceans was confirmed by cloning preproTRP from the spiny lobster Panulirus interruptus. RT-PCR and Northern blotting analyses suggested that the crayfish preproTRP mRNA is expressed throughout the nervous system, and in situ hybridization studies of the brain revealed that the transcript predominantly localizes to cell clusters 11 (dorsal lateral cells) and 9 (ventral lateral cells).

A new concept relating to the purification protocol for biological proteins and peptides has been designed as “topological mass spectrometry analysis,” in combination with MALDI-TOF MS using slices of tissues, chromatographic purification from the extract of tissues, molecular cloning for the determination of the precursor structure, and capillary LC-MS/MS analysis for elucidation of its posttranslational modifications. In an actual application, we identified an α-amidated neuropeptide from the red swamp crayfish ( Procambarus clarkii ) brain. Initially, an MS number of around m / z 1382 was found by the direct MALDI-TOF MS analysis with slices of the accessory lobe of the brain. After two steps of reversed-phase HPLC separation with brain extract, the structure of a 1381 Da peptide was sequenced to the GYRKPPFNGSIFamide (named crustacean-SIFamide). Subsequently, the cDNA has been characterized and encodes a 76 amino acid precursor protein that contains a signal sequence, one copy of GYRKPPFNGSIFG and one additional peptide. The RT-PCR analysis implied that the mRNA of the neuropeptide was expressed throughout the nervous system of the crayfish. Furthermore, immunostaining demonstrated that the neuropeptide is distributed in the olfactory lobe, accessory lobe, olfactory globular tract, and olfactory lobe cells. In addition, database searches revealed that there are homologous sequences of the AYRKPPFNGSIFamide in the genome library of fruitfly Drosophila melanogaster and AYRKPPFNGSLFamide isolated from the grey fleshfly Neobellieria bullata , and GYRKPPFNGSIFamide isolated from the giant tiger prawn Penaeus monodon . These results suggested that the neuropeptide family might be widely distributed in arthropods and plays a significant role in the nervous system.

Using a combination of MALDI-TOF and on-line capillary HPLC/Q-Tof mass spectroscopy, we identified and determined the amino acid sequence of a novel neuropeptide in the brain of the honeybee Apis mellifera L., termed AmTRP peptide (Apis mellifera tachykinin-related peptide), related to insect tachykinin. A cDNA for a prepro-protein (prepro-AmTRP) of AmTRP was isolated and determined to encode seven AmTRPs 1-7. Northern blot analysis indicated that the prepro-AmTRP gene is expressed differentially in the nurse bee, forager, queen and drone heads. Strong expression was detected in the queen and forager heads, while weak and almost no significant expression was detected in the nurse and drone heads, respectively. These results suggest that AmTRP peptide functions as a neuromodulator and/or hormone, associated with sex-specific or age/division of labour-selective behaviour and/or physiology of the honeybees.

We have recently identified a tachykinin-related peptide (AmTRP) from the mushroom bodies (MBs) of the brain of the honeybee Apis mellifera L. by using direct matrix-assisted laser desorption/ionization with time-of-flight mass spectometry and have isolated its cDNA. Here, we have examined prepro-AmTRP gene expression in the honeybee brain by using in situ hybridization. The prepro-AmTRP gene is expressed predominantly in the MBs and in some neurons located in the optic and antennal lobes. cDNA microarray studies have revealed that AmTRP expression is enriched in the MBs compared with other brain regions. There is no difference in AmTRP-expressing cells among worker, queen, and drone brains, suggesting that the cell types that express the prepro-AmTRP gene do not change according to division of labor, sex, or caste. The unique expression pattern of the prepro-AmTRP gene suggests that AmTRPs function as neuromodulators in the MBs of the honeybee brain.

DL-threo-beta-benzyloxyaspartate (DL-TBOA) is a non-transportable blocker of the glutamate transporters that serves as an indispensable tool for the investigation of the physiological roles of the transporters. To examine the precise interaction between a blocker and the transporters, we synthesized the optically pure isomers (L- and D-TBOA) and its erythro-isomers. L-TBOA is the most potent blocker for the human excitatory amino acid transporters (EAAT1-3), while D-TBOA revealed a difference in the pharmacophores between EAAT1 and EAAT3. We also synthesized the substituent variants (methyl or naphthylmethyl derivatives) of L-TBOA. The results obtained here suggest that bulky substituents are crucial for non-transportable blockers.

We developed a strategy for the exploration of brain peptides in the red swamp crayfish, Procambarus clarkii, utilizing the combined techniques of matrix-assisted laser desorption/ionization with time-of-flight mass spectrometry (MALDI-TOF MS), molecular cloning, and on-line capillary reversed-phase HPLC/quadrupole orthogonal acceleration time-of-flight (Q-Tof)-MS. We initially performed direct MALDI-TOF MS analysis with slices of the brain. The MS spectra from a slice of the olfactory lobe indicated that an orcokinin (NFDEIDRSGFGFN) occurs in this species. Subsequently, its occurrence was confirmed by molecular cloning of the cDNAs encoding the precursor protein of orcokinin. The deduced amino acid sequences indicated that there are two different types of preproorcokinins. Preproorcokinin A (251 residues long) contains not only seven copies of orcokinin but also two copies of NFDEIDRSGFGFV and one copy each of NFDEIDRSGFGFA, NFDEIDRTGFGFH, and FDAFTTGFGHS. The former three peptides were previously isolated from another crayfish, Orconectes limosus, and/or the shore crab, Carcinus maenas, and the latter two were novel. Preproorcokinin B (266) harbors one additional orcokinin. All sequences of the peptides are flanked by dibasic sequences which are the consensus signal for processing. Moreover, brain extract was subjected to Sephadex G-25 and, subsequently, to on-line capillary reversed-phase HPLC/Q-Tof MS analysis. From the LC-MS analysis, the molecular weights of orcokinin, NFDEIDRSGFGFV, NFDEIDRSGFGFA, NFDEIDRTGFGFH, and FDAFTTGFGHS were identified as the doubly charged ions at m/z 759.37, 751.92, 737.86, 777.90, and 593.78, respectively. In addition, the sequences were assigned by the collision-induced dissociation spectra using the doubly charged ions in the LC-MS/MS analysis. These data suggest that orcokinin and its related peptides are especially abundant in the olfactory lobe and are synthesized and processed from the two types of preproorcokinins in the crayfish brain.

Achatin-I and fulicin, isolated from the ganglia and atria of the giant land snail Achatina fulica, are a tetrapeptide and pentapeptide containing a d-Phe and d-Asn at position 2, respectively. We succeeded in cloning a cDNA encoding a precursor of achatin-I from the Achatina ganglia, revealing that the d-Phe present in achatin-I is coded by a common l-Phe codon, TTT or TTC. The deduced polypeptide was found to comprise seven repeats of the achatin sequence GFAD and one analog GFGD flanked on both sides by the typical endoproteolytic site KR. Northern blot analysis of transcripts and Southern blot analysis of reverse transcription (RT)-PCR products demonstrated that achatin-I mRNA was localized in the subesophageal ganglia, whereas expression of fulicin mRNA was detected in the atrium as well as in the subesophageal ganglia. Furthermore, localization of the achatin gene transcript in the right and left pedal ganglia compartments was shown by in situ hybridization on sections of subesophageal ganglia, whereas the fulicin transcript was observed in the right and left parietal ganglia. These data suggested that achatin-I plays an essential role in the regulation of the heart as a neurotransmitter or neurohormone through production in the pedal ganglia and transport to the atrium, whereas fulicin serves not only as a neurotransmitter or neurohormone but also as a novel atrial hormone.

Yasuda-Kamatani, Y., M. Kobayashi, A. Yasuda, T. Fujita, H. Minakata, K. Nomoto, M. Nakamura and F. Sakiyama. A novel d -amino acid-containing peptide, fulyal, coexists with fulicin gene-related peptides in Achatina atria. Peptides 18(3) 347–354, 1997.—Fulicin (Phe- d -Asn-Glu-Phe-Val-NH 2 ) is a neuropeptide from ganglia of the African giant snail ( Achatina fulica ). Previously, the sequences of nine fulicin gene-related peptides (FGRP-1 to -9) have been predicted from the cDNA encoding the ganglia fulicin precursor and the transcripts have been detectable in the heart. We synthesized twenty peptides related to fulicin and FGRPs containing either an l - or a d -amino acid at position 2 and used them to identify FGRPs in atrial extracts. We identified ten α -amidated peptides, including fulicin and confirmed their structures as follows: Tyr-Ala-Glu-Phe-Leu-NH 2 (FGRP-9), [ d -Ala 2 ]FGRP-9 (fulyal), [ l -Asn 2 ]fulicin, fulicin, Ser-Tyr-Asp-Phe-Val-NH 2 (FGRP-2), Thr-Tyr-Asp-Phe-Leu-NH 2 (FGRP-3), Tyr-Asp-Phe-Ile-NH 2 (FGRP-5), Ser-Pro-Tyr-Asp-Phe-Ile-NH 2 (FGRP-6), Asn-Tyr-Asp-Phe-Val-NH 2 (FGRP-7) and Ser-Pro-Tyr-Asp-Phe-Val-NH 2 (FGRP-8). We analyzed the biological activities of synthetic FGRPs using the snail penis retractor muscle. The results revealed that fulyal remarkably potentiated the tetanic contraction at concentrations as low as 10 −12 M. FGRP-9 was about 10,000-fold less potent. Fulyal, like fulicin, seems to undergo preferential maturation to participate in the penis retractor muscle contraction as a neuropeptide containing a d -amino acid.

Fulicin (Phe-D-Asn-Glu-Phe-Val-NH2) is an endogenous neuropeptide containing a D-amino acid from ganglia of the African giant snail Achatina fulica. We have cloned a novel cDNA (1,995 nucleotides) encoding a fulicin precursor from the snail cerebral and subesophageal ganglia. The fulicin precursor protein (357 amino acids) contains one copy of fulicin and at least nine other putative alpha-amidated neuropeptides composed of four to six amino acid residues. Seven of the nine neuropeptides were novel, and the other two had the same structures as Mytilus inhibitory peptide-related peptides previously isolated from the ganglia of Helix pomatia. All sequences of 10 peptides are flanked by Lys-Arg(Lys) at the N-terminus and by Gly-Lys-Arg(Lys) at the C-terminus. Nucleotide sequence analysis revealed that D-Asn present in fulicin is encoded by the usual L-Asn codon (AAT). Although fulicin has as yet only been isolated from the central ganglia. RNA blot analysis revealed that single transcripts of approximately 2.0 kb in size also exist in the ventricles and atria. These results suggest that fulicin and related peptides are produced in neurons and the heart by the processing of a ribosomally made precursor, although the mechanism of in-chain epimerization remains unclear.

Two almost identical trypsin isoinhibitors, LLDTI-I and LLDTI-II, from bottle gourd (Lagenaria leucantha Pusby var. Depressa Makino) seeds were purified by acetone precipitation, gel filtration and reversed phase chromatography. LLDTI-I and LLDTI-II consist of 30 and 29 amino acid residues, respectively, and have identical sequences, except that LLDTI-I has one additional pyroglutamic acid residue at N-terminus. Both proteins are strong inhibitors of bovine trypsin, with Ki values of 2.4·10−10 M (LLDTI-I) and 9.6·10−11 M (LLDTI-II). Amino acid are sequences are as follows: Download : Download full-size image

The molecular conformation of achatin-II neutral form (H-Gly-Phe-Ala-Asp-OH), an endogenous peptide from the Achatina fulica ganglia, was elucidated by X-ray crystal analysis. The molecule takes an extended β-pleated structure stabilized by 5 intermolecular hydrogen bonds with the antiparallely arranged molecules. This is in contrast with the turn conformation of a neuroactive achatin-I (H-Gly-d-Phe-Ala-Asp-OH) [(1992) FEBS Lett. 276, 95–97]. The conformational comparison of both of the molecules makes clear the structural role which d-Phe residue of achatin-I plays in forming a definite active form.