A neurohormone regulating both methyl farnesoate synthesis and glucose metabolism in a crustacean

Methyl farnesoate (MF) has been identified as a juvenile hormone-like compound in crustacea which has central roles in the regulation of development and reproduction. To study the regulation of MF synthesis, we isolated a neuropeptide which inhibits MF synthesis from the neurohemal organ-sinus gland X-organ complex of the spider crab Libinia emarginata. The primary structure of this neuropeptide has been determined. It has 72 amino acid residues (deduced molecular mass 8490.5 Da) with pyroglutamic acid at the N-terminus and NH3 at the C-terminus. It shares a high percentage of sequence identity with other sinus gland neuropeptids which form the unique family of CHH neuropeptides of crustacea. Activity studies showed that this neurohormone has dual effects: it inhibited MF synthesis in vitro and had hyperglycemic activity when injected into crabs.

Probing the structure of the ligand binding cavity of lipocalins by fluorescence spectroscopy

The lipocalin superfamily constitutes a phylogenetically conserved group of more than 40 proteins that function in the binding and transport of a variety of physiologically important ligands. Members of this family subserve diverse functions as carriers of retinoids (retinol binding protein), odorants (odorant binding proteins), chromophores (insecticyanin, INS), pheromones (aphrodisin) and sterols (apolipoprotein D, apoD). Despite the pivotal importance of the ligand binding function of these proteins, a suitable approach for characterizing the molecular determinants of such binding has not been available. In studies using three homogeneously purified lipocalins INS, beta-lactoglobulin (BLG) and human apoD, we find that the fluorescence reporter BIS (1,1'-bi(4-anilino) naphthalene-5,5'-disulfonic acid) is an ideal candidate for use in rapid kinetic experiments and in fluorescence resonance energy transfer (FRET). These methods require only small amounts of reagents and yield molecular coordinates of the ligand binding cavity of lipocalins in solution that are in remarkably close agreement to those obtained from crystallographic work with solids. Extremely fast ligand binding dynamics is indicated.

Immunochemical demonstration of Eisenia tetradecapeptide, a bioactive peptide isolated from the gut of the earthworm Eisenia foetida, in tissues of the earthworm

The quantity and localization of Eisenia tetradecapeptide which was isolated from the gut of the earthworm Eisenia foetida were examined in tissues of the same species by enzyme-linked immunosorbent assay and immunohistochemistry. Analysis by enzyme-linked immunosorbent assay showed that Eisenia-tetradecapeptide-like immunoreactivity was present in both the central nervous system (cerebral ganglion, subesophageal ganglion, ventral ganglia, and ventral nerve cord) and the gut (esophagus, crop, gizzard, and intestine). The central nervous system contained a higher amount of Eisenia-tetradecapeptide-like immunoreactivity (1.3 pmol/mg wet weight) than the gut (0.2-0.6 pmol/mg wet weight). Eisenia-tetradecapeptide-like immunoreactivity was scarcely detected in the body-wall muscle, nephridia, and sexual organs (testis, ovary, seminal vesicle, and ovisac). Immunohistochemical analysis demonstrated that intense Eisenia-tetradecapeptide-like immunopositive cells and nerve fibers were present in the central nervous system. Immunoreactivity was found in the epithelial cells lining the esophagus and in the submucous plexus in various parts of the gut. Thus, the present study suggests that Eisenia tetradecapeptide is a neuropeptide and/or peptide hormone present in both the central nervous system and the gut of the earthworm and that its role involves the regulation of gut motility.

A new structural class of serine protease inhibitors revealed by the structure of the hirustasin-kallikrein complex

BACKGROUND

Hirustasin belongs to a class of serine protease inhibitors characterized by a well conserved pattern of cysteine residues. Unlike the closely related inhibitors, antistasin/ghilanten and guamerin, which are selective for coagulation factor Xa or neutrophil elastase, hirustasin binds specifically to tissue kallikrein. The conservation of the pattern of cysteine residues and the significant sequence homology suggest that these related inhibitors possess a similar three-dimensional structure to hirustasin.

RESULTS

The crystal structure of the complex between tissue kallikrein and hirustasin was analyzed at 2.4 resolution. Hirustasin folds into a brick-like structure that is dominated by five disulfide bridges and is sparse in secondary structural elements. The cysteine residues are connected in an abab cdecde pattern that causes the polypeptide chain to fold into two similar motifs. As a hydrophobic core is absent from hirustasin the disulfide bridges maintain the tertiary structure and present the primary binding loop to the active site of the protease. The general structural topography and disulfide connectivity of hirustasin has not previously been described.

CONCLUSIONS

The crystal structure of the kallikrein-hirustasin complex reveals that hirustasin differs from other serine protease inhibitors in its conformation and its disulfide bond connectivity, making it the prototype for a new class of inhibitor. The disulfide pattern shows that the structure consists of two domains, but only the C-terminal domain interacts with the protease. The disulfide pattern of the N-terminal domain is related to the pattern found in other proteins. Kallikrein recognizes hirustasin by the formation of an antiparallel beta sheet between the protease and the inhibitor. The P1 arginine binds in a deep negatively charged pocket of the enzyme. An additional pocket at the periphery of the active site accommodates the sidechain of the P4 valine.

Crustacean hyperglycaemic hormone in the nervous system of the primitive crustacean species Daphnia magna and Artemia salina (Crustacea: Branchiopoda)

Crustacean hyperglycaemic hormone-immunoreactive neuronal systems are detected in the central and peripheral nervous systems of two entomostracan crustaceans, Daphnia magna and Artemia salina, by immunocytochemistry using specific antisera against crustacean hyperglycaemic hormones of the decapod crustaceans Orconectes limosus and Carcinus maenas. In D. magna, four small putative interneurones are detected in the brain. In the thorax, ten bipolar peripheral neurones are stained by both antisera. They are obviously segmental homologues with centrally projecting axons that form interdigitating varicose fibres and terminals in putative neurohaemal areas next to the surface of the anterior part of the thoracic ganglia. Similar immunopositive neurones occur both in the central and peripheral nervous systems of A. salina. A total of five groups of neurones occur in the protocerebrum, the deutocerebrum and the mandibular ganglion. Some of the protocerebral neurones are bipolar and project to the dorsal frontal organ. A single pair of peripheral multipolar neurones in the maxillary segment projects centrally into the ventral nerve cord and innervates unidentified somatic muscles and tissues in the maxillary and the first appendage segments. None of the brain neurones in both species show similarities to decapod X-organ sinus gland neurosecretory neurones. Chromatography of brain extracts of D. magna combined with immunodot blotting revealed two strongly immunoreactive fractions at retention times close to that of the crustacean hyperglycaemic hormone of crayfish. Moreover, preabsorption controls suggest that the cross-reacting peptides of D. magna and A. salina are structurally closely related to those of decapods.

Distinct sequences of AKH/RPCH family members in beetle (Scarabaeus-species) corpus cardiacum contain three aromatic amino acid residues

Two forms of AKH/RPCH family peptides have been identified from the corpus cardiacum of various dung beetle species of the genus Scarabaeus and the related genus Gareta by using RP-HPLC. The primary structures were established in two species by automated Edman degradation and mass spectral analysis as blocked octapeptides containing three aromatic amino acids (at positions 2, 4 and 8): peptide I: pGlu-Phe-Asn-Tyr-Ser-Pro-Asp-Trp-NH2; peptide II: pGlu-Phe-Asn-Tyr-Ser-Pro-Val-Trp-NH2. The peptides were not active in the heterologous adipokinetic bioassay in locusts, but increased the concentration of proline in the haemolymph of Scarabaeus beetles. Since proline is also used in these species to provide the energy for contraction of the flight muscles during flight, it is proposed that the distinct peptides characterized here are responsible for the hormonal control of proline homeostasis.

Recombinant hirustasin: production in yeast, crystallization, and interaction with serine proteases

A synthetic gene coding for the 55-amino acid protein hirustasin, a novel tissue kallikrein inhibitor from the leech Hirudo medicinalis, was generated by polymerase chain reaction using overlapping oligonucleotides, fused to the yeast alpha-factor leader sequence and expressed in Saccharomyces cerevisiae. Recombinant hirustasin was secreted mainly as incompletely processed fusion protein, but could be processed in vitro using a soluble variant of the yeast yscF protease. The processed hirustasin was purified to better than 97% purity. N-terminal sequence analysis and electrospray ionization mass spectrometry confirmed a correctly processed N-terminus and the expected amino acid sequence and molecular mass. The biological activity of recombinant hirustasin was identical to that of the authentic leech protein. Crystallized hirustasin alone and in complex with tissue kallikrein diffracted beyond 1.4 A and 2.4 A, respectively. In order to define the reactive site of the inhibitor, the interaction of hirustasin with kallikrein, chymotrypsin, and trypsin was investigated by monitoring complex formation in solution as well as proteolytic cleavage of the inhibitor. During incubation with high, nearly equimolar concentration of tissue kallikrein, hirustasin was cleaved mainly at the peptide bond between Arg 30 and Ile 31, the putative reactive site, to yield a modified inhibitor. In the corresponding complex with chymotrypsin, mainly uncleaved hirustasin was found and cleaved hirustasin species accumulated only slowly. Incubation with trypsin led to several proteolytic cleavages in hirustasin with the primary scissile peptide bond located between Arg 30 and Ile 31. Hirustasin appears to fall into the class of protease inhibitors displaying temporary inhibition.

Fine structural and immunocytochemical studies on the eyeless aesthetes of Leptochiton algesirensis, with comparison to Leptochiton cancellatus (Mollusca, Polyplacophora)

The aesthetes of Leptochiton algesirensis (Capellini, 1859) and Leptochiton cancellatus (Sowerby, 1840) consist of six to eight microaesthetes surrounding one macroaesthete. The monocellular microaesthetes include many microtubules, neurosecretory vesicles, and unperforated, subsidiary caps. Basally they are in contact with tiny nerve processes via probably electrical synapses. Each macroaesthete consists of a perforated apical cap and various cell types: flattened peripheral cells, various types of mucous cells, and three or four monociliary sensory cells. Although lacking photoreceptors, the aesthetes of Leptochiton algesirensis combine storage-secretory and sensory functions. The latter function is confirmed by positive immunoreactions against (neuro-)tubulin and synaptophysine. The high degree of structural and functional similarity between polyplacophoran aesthetes and the analogous caeca of brachiopods is demonstrated.

Cell type-specific sorting of neuropeptides: a mechanism to modulate peptide composition of large dense-core vesicles

The CNS of Lymnaea stagnalis contains two populations of egg-laying hormone (ELH)-producing neurons that differ in size and topology. In type I neurons, all peptides located C-terminally from the cleavage site Arg-Ser-Arg-Arg180-183 are sorted into secretory large dense-core vesicles (LDCV), whereas N-terminal-located peptides accumulate in a distinct type of vesicle, the large electrondense granule (LEG). Via immunoelectron microscopy, we now show that the second population of ELH-producing neurons, type II neurons, lack LEG and incorporate all proELH-derived peptides into LDCV. This finding provides the first example of a cell type-specific sorting of neuropeptides into LDCV. Furthermore, we provide evidence that LEG are formed through a differential condensation process in the trans-Golgi network and that these bodies are ultimately degraded. Analysis of the endoprotease composition of the two types of proELH-producing neurons suggests that the formation of LEG, and consequently the retention of N-terminal peptides from the secretory pathway, requires the action of a furin-like protein.

High affinity endotoxin-binding and neutralizing peptides based on the crystal structure of recombinant Limulus anti-lipopolysaccharide factor

Lipid A, the conserved portion of endotoxin or lipopolysaccharide, is the major mediator of septic shock, and therefore endotoxin-neutralizing molecules could have important clinical applications. The crystal structure of recombinant Limulus anti-lipopolysaccharide factor (rLALF) (Hoess, A., Watson, S., Siber, G. R., and Liddington, R. (1993) EMBO J. 12, 3351-3356), has been used to design synthetic peptides comprising different parts of the exposed amphipathic loop in the proposed endotoxin-binding domain of rLALF. We investigated the minimal requirements of rLALF for endotoxin and lipid A binding with linear 10-mer peptides. Only one linear peptide, corresponding to amino acids 36-45 of rLALF, was able to bind lipid A and endotoxin above background levels. Cyclic peptides, however, bind lipid A and endotoxin with high affinity, presumably by mimicking the three dimensional characteristics of the exposed hairpin loop. The cyclic peptide including amino acids 36-47, LALF-14, has a lipid A binding activity comparable to the high affinity endotoxin-binding peptide polymyxin B. LALF-14 has an improved serum half-life compared with its linear counterpart, and it is not toxic for cultured human monocytes or red blood cells. In mice, it blocks tumor necrosis factor-alpha induction after endotoxin challenge. The characterization of the minimal endotoxin-binding domain of rLALF and, importantly, its structure provided a basis for designing small molecules that could have prophylactic and/or therapeutic properties in humans for the management of septic shock.

Does the N-terminal pyroglutamate residue have any physiological significance for crab hyperglycemic neuropeptides?

A characteristic feature of all crustacean hyperglycemic hormones (CHH) is that they are always present in the sinus gland as multiple forms or isoforms. The amino acid sequence of the minor form of CHH from the green shore crab, Carcinus maenas, was determined by automated microsequencing and MS, and was almost identical to that of the major form, except that the N-terminal residue was glutamine rather than pyroglutamate. Limited analysis (electrospray MS and amino acid composition) of the two corresponding forms of CHH from the edible crab, Cancer pagurus, suggested a similar phenomenon in this species. For C. maenas, both forms were indistinguishable in terms of their ability to cause sustained hyperglycemia in vivo and repression of ecdysteroid synthesis in vitro. Similarly, the two forms were immunologically identical in RIA, and exhibited similar binding characteristics in competitive-receptor-binding assays. CD studies showed only minor differences in presumed secondary structure. In vitro release experiments with isolated sinus glands demonstrated that both forms are probably released in a stoichiometric manner and that both peptides are present in the haemolymph at the same ratio as that in the sinus gland. Preliminary results suggest that the in vivo clearance/degradation rates of both peptides are similar. The unblocked (Gln) terminus is of particular significance, since the presence of this amino acid indicates that this peptide is derived from a precursor that does not possess the same structure of those of established preproCHH, or that N-terminal processing is slow, which results in the presence of unblocked CHH in sinus glands. The similar biological activity of the unblocked CHH to that of the blocked CHH suggests that the N-terminal pyroglutamate residue has no obvious biological significance (with respect to the known functions of CHH), an observation which is in contrast to the widely accepted paradigms concerning the stability and biological activity of N-terminally blocked and unblocked peptides.

Nematode FMRFamide-related peptide (FaRP)-systems: occurrence, distribution and physiology

The application of rational (mechanism-based) approaches to anthelmintic discovery requires information about target proteins which are pharmacologically distinguishable from their vertebrate homologs. In helminths, several such targets (e.g., beta-tubulin, ATP-generating enzymes, cholinergic receptors, CI- channels) have been characterized only after the discovery, through empirical screening, of compounds that interfere with their function. From the perspective of anthelmintic discovery, the utility of these targets is diminishing due to the emergence of drug-resistant strains of parasites. This has motivated the search for compounds with novel modes-of-action. Recent basic research in helminth physiology and biochemistry has identified several potential targets for rational anthelmintic discovery, including receptors for FMRFamide-related peptides (FaRPs). To date, over 20 different nematode FaRPs have been identified and these peptides, which are broadly distributed in helminths, have been localized to all of the major neuronal subtypes in nematodes. The FaRPs that have been examined have been found profoundly to affect somatic muscle function in gastrointestinal nematodes. In this respect, complex inhibitory and excitatory actions have been identified for a number of these peptides. Although the transduction pathways for any of these peptides remain to be elucidated, the available evidence indicates that nematode FaRPs have numerous mechanisms of action. The employment of nematode neuropeptide receptors in mechanism-based screens has immense potential in the identification of novel anthelmintics.

Characterization of hyperglycemic and molt-inhibiting activity from sinus glands of the penaeid shrimp Penaeus vannamei

To design a homologous bioassay for the molt-inhibiting hormone and the crustacean hyperglycemic hormone of the shrimp Penaeus vannamei, the effect of sinus gland homogenate (SGh), in vitro, on ecdysteroid production by Y-organs (YOs), and the effect of the injection of SGh, in vivo, on the glycemia of shrimps have been investigated. Addition of SGh to incubation medium of shrimp YOs dose dependently reduced, within a few hours, ecdysteroid release into the medium. Moreover, inhibition by SGh decreases drastically in YOs from animals in late premolt stages, when there is maximal ecdysteroid production. Injection of SGh into shrimps evokes a hyperglycemic response maximal after 2 hr. Immunoadsorption of SGh with an anti-Homarus americanus cHHA antiserum inhibited both biological activities of the homogenate. After fractionation of acidic sinus gland extract by RP-HPLC, the maximal response in both bioassays was associated with the major UV absorbent peak, which was also the major immunoreactive peak when tested by ELISA with the anti-lobster cHHA. After a further purification step, the molecular mass of the bioactive and immunoreactive peptide was found to be 8627 +/- 0.3 Da by electrospray ionization mass spectrometry. The amino acid sequence of the first 38 residues of this peptide was established by gas-phase microsequencing. This sequence shows 55% homology with the first 38 residues of the lobster cHHA.

Isolation and amino acid sequence of a molt-inhibiting hormone from the American crayfish, Procambarus clarkii

A molt-inhibiting hormone (Prc-MIH) was isolated from the sinus glands of the American crayfish, Procambarus clarkii, and its amino acid sequence was determined. It comprised 75 amino acid residues and had an amidated carboxyl terminus. The amino acid sequence was much more similar to MIH of the shore crab (Cam-MIH) than to MIH of the American lobster (Hoa-MIH).

Determination of the amino acid sequence of the moult-inhibiting hormone from the edible crab, Cancer pagurus

Putative moult-inhibiting hormone (MIH) from sinus glands of the edible crab Cancer pagurus was characterized by high-performance liquid chromatography, followed by fractional bioassay (inhibition of ecdysteroid synthesis by Y-organs) and immunoassay (using antisera raised against Carcinus MIH). This peptide was fully sequenced by automated Edman degradation of endoproteinase-derived fragments. C. pagurus MIH is a 78 residue peptide (M(r) 9194), with free N- and C-termini and three intrachain disulphide bridges. Comparison with previously published MIH sequences confirms a high degree of sequence identity (c. 80%), supporting the view that brachyurans (crabs), possess distinct, structurally similar MIH neuropeptides.

Enhanced antiopiate activity and enzyme resistance in a peptidomimetic of FMRFamide containing E-2,3-methanomethionine and E-2,3-methanophenylalanine

FMRFamide is a molluscan peptide that has shown antiopiate activity in a number of mammalian test systems. Peptidomimetics of FMRFamide substituted with conformationally constrained stereoisomers of Z-2,3-methanomethionine or E-2,3-methanomethionine precipitated abstinence syndrome far more potently than FMRFamide itself. The current study determined the effect on antiopiate potency of an additional rigid substitution. A peptidomimetic containing a stereoisomer of E-2,3-methanomethionine was compared with a peptidomimetic additionally substituted at the C-terminal with E-2,3-methanophenylalanine. Morphine abstinence signs were observed after varying doses (0.125-25.0 micrograms) of these two peptidomimetics were injected into the third ventricle of morphine-dependent rats. The peptidomimetic containing both rigid substitutions was far more potent than the peptidomimetic of FMRFamide containing methanomethionine alone. The increased potency appears to be related to enzyme resistance rather than receptor affinity.

Purification, primary structure, and neuronal localization of cerebral peptide 1 from Aplysia

We are investigating peptidergic neurotransmission between ganglia in the Aplysia CNS. Neurons in the cerebral ganglia of Aplysia synthesize [35S]methionine-labeled peptides, which are transported to other central ganglia by fast axonal transport. We report the characterization of one of these peptides, termed cerebral peptide 1 (CP1). Transported [35S]methionine-labeled CP1 was used as a probe for the purification of CP1 from the pooled extracts of 1000 cerebral ganglia using three sequential modes of RP-HPLC. Amino acid sequence analysis by automated Edman degradation yielded the following sequence: Phe-Ser-Gly-Leu-Met-Ser-Glu-Gly-Ser-Ser-Leu-Glu-Ala. This sequence was consistent with data from amino acid composition analysis and FAB-MS of the purified peptide. In addition, a synthetic peptide with the proposed sequence coeluted with [35S]methionine-labeled native CP1 using the three RP-HPLC conditions used in the purification. Antisera raised against synthetic CP1 stained about 90 neuronal cell bodies in the cerebral ganglion including those of the asymmetric H cluster. Extracts of the H cluster dissected from ganglia incubated in [35S]methionine synthesized a radiolabeled peptide that coeluted with synthetic CP1, indicating that these neurons indeed synthesize authentic CP1. The other major ganglia each contained only a few CP1-immunoreactive neurons. The neuropil of each ganglion contains both smooth and varicose-immunoreactive fibers. Thus, CP1 is broadly distributed within the Aplysia CNS and may be a new peptide transmitter.

A cysteine-rich serine protease inhibitor (Guamerin II) from the non-blood sucking leech Whitmania edentula: biochemical characterization and amino acid sequence analysis

A cysteine-rich serine protease inhibitor (Guamerin II) was isolated from the non-blood sucking leech Whitmania edentula. The new inhibitor was identified as a low molecular weight (6,012 Da) polypeptide with some sequence similarities to antistasin, hirustasin and guamerin. The inhibitor contained 56 amino acid residues with 76.8% sequence similarity to guamerin, 48.2% to hirustasin and 28.6% to the first domain of antistasin. This new inhibitor was the first completely sequenced serine protease inhibitor from a non-blood sucking leech. Analysis of the inhibitor revealed that it was active against neutrophil elastase and chymotrypsin, but had no activity against a variety of other proteases. The P1 reactive site residue was identified as methionine and the residues surrounding the P1 site were hydrophobic amino acids. The primary structure of the inhibitor showed no similarity to well-known elastase inhibitors from leeches such as eglin.

Isolation and structural determination of seminal vesicle-specific peptides of the terrestrial isopod, Armadillidium vulgare

During the course of purifying the androgenic gland hormone of the terrestrial isopod, Armadillidium vulgare, that induces post-embryonic sex differentiation, four structurally related peptides were obtained and their structures determined by a combination of microsequence and mass spectral analyses. These peptides were found to exist speciffically in the seminal vesicle and vas deferens by a Western blot analysis, therefore being designated as seminal vesicle-specific peptides (SVSPs). They had essentially the same amino acid sequences but differed from one another in the truncation of several residues at the N-terminus and of one residue at the C-terminus, and in the modification of glutamine to pyroglutamate at the N-terminus. The longest peptides, SVSP-4, consisted of 60 amino acid residues with two intramolecular disulfide bridges. There is no significant homology with any other vertebrate or invertebrate peptides.

Effects of annetocin, an oxytocin-related peptide isolated from the earthworm Eisenia foetida, and some putative neurotransmitters on gut motility of the earthworm

Annetocin, an oxytocin-related peptide recently isolated from the lumbricid earthworm Eisenia foetida, and putative transmitter substances were examined for their effects on rhythmic, spontaneous contractions of isolated gut preparations of the earthworm. Significant, dose-dependent effects of the following substances were observed: acetylcholine (ACh), gamma-aminobutyric acid (GABA), and dopamine were excitatory, while serotonin (5-HT) and octopamine were inhibitory. Annetocin, oxytocin, and vasotocin stimulated spontaneous contraction of the earthworm gut, annetocin being approximately 10-fold more potent than oxytocin or vasotocin. However, arginine-vasopressin (Arg-vasopressin), lysine-vasopressin (Lys-vasopressin), tocinoic acid (N-terminal hexapeptide fragment of oxytocin), and MSH release-inhibiting factor (MIF; C-terminal tripeptide fragment of oxytocin) did not show any effect on the earthworm gut motility. On the other hand, oxytocin, vasotocin, Arg-vasopressin, Lys-vasopressin, and tocinoic acid caused spontaneous contractions of isolated rat uterine preparations, where the potency was in this order, while annetocin and MIF exerted no oxytocic activity on the uterus. Dose-response relationship of the effects of annetocin and its related peptides on the annelid and mammalian systems shows that amino acid residue at the third position of these peptides is important for exertion of excitatory action on the smooth muscle systems. The results in the present study suggest that receptors for annetocin and for GABA on the earthworm gut, unlike those for ACh, desensitize during continuous exposure to these substances.

Inhibition of endotoxin-induced activation of the coagulation and fibrinolytic pathways using a recombinant endotoxin-binding protein (rBPI23)

A recombinant endotoxin-neutralizing protein, rBPI23, was shown to partially prevent endotoxin-induced activation of the fibrinolytic and coagulation systems in experimental endotoxemia in humans. In a placebo-controlled, blinded crossover study, eight volunteers were challenged twice with an intravenous bolus injection of endotoxin (40 EU/kg of body weight) and concurrently received either rBPI23 (1 mg/kg) or placebo (human serum albumin, 0.2 mg/kg). rBPI23 treatment significantly lowered the endotoxin-induced fibrinolytic response, ie, reduced the release of tissue-type plasminogen activator, urokinase-type plasminogen activator, plasminogen activator inhibitor antigen, and complex formation of plasmin alpha 2-antiplasmin (P = .0078 for each). Plasminogen activator inhibitor activity was also reduced, but not significantly according to the Hochberg method (P = .0304). The endotoxin-induced activation of the procoagulant state as reflected by increase in F1 + 2 fragments and TAT complexes was blunted by rBPI23 infusion (P = .0391 [not significant according to the Hochberg method] and .0078, respectively). These results indicate that rBPI23 is capable of reducing both the activation of the fibrinolytic and the coagulation systems after low-dose endotoxin infusion in humans.

Isolation and characterization of guamerin, a new human leukocyte elastase inhibitor from Hirudo nipponia

A new human leukocyte elastase inhibitor was extracted and purified from a Korean native leech Hirudo nipponia. The inhibitor, called guamerin, has a molecular weight of 6,110 and shows inhibition constant (Ki) of 8.1 x 10(-14) M. It is stable at a wide range of pH from 1 to 11 and heat-stable up to 90 degrees C. The complete amino acid sequence of guamerin reveals a cysteine-rich polypeptide of 57 amino acid residues that shows no similarity to any known elastase inhibitors but has 51% sequence homology with hirustasin. Guamerin has identical spacing of 10 cysteine residues as antistasin-type serine proteinase inhibitors, but the P1 reactive site residue is Met36 instead of Arg. The neighboring sequence of the reactive site consists primarily of hydrophobic amino acid residues. Based on examinations of the target proteinases and the reactive site specificity, guamerin is a new low molecular weight protein that inhibits elastases.

Rational design of anticonvulsants: a quantum pharmacologic study of the ion channel-modulating FMRFamide tetrapeptide as an endogenous anticonvulsant

We applied the computational techniques of quantum pharmacology to examine molecular conformations (shapes and geometries) of the tetrapeptide FMR-Famide (L-Phe-L-Met-L-Arg-L-Phe-NH2), determining the geometric features necessary for anticonvulsant activity. The rigorous tiered hierarchical approach used molecular mechanics, molecular dynamics, and semiempirical quantum mechanics calculational methods. Low-energy conformations showed pertinent conformational information to be considered in the rational design of novel anticonvulsants. The FMRFamide peptide backbone assumes a bent but primary planar geometry. Distinct polar and nonpolar regions are created as the two Phe residues occupy one "face" of the bent conformation, while the Met and Arg residues occupy the opposite face. The aromatic rings point away from each other along the backbone, and this separation is consistent among the low-energy conformations at approximately 11-12 A. The Met side chain interacts with neither the peptide backbone nor the side chains of other residues. Molecular mechanics and semiempirical quantum mechanics calculations predict limited variation in the orientation of the Arg side chain.

Amino acid sequence of the minor isomorph of the crustacean hyperglycemic hormone (CHH-II) of the Mexican crayfish Procambarus bouvieri (Ortmann): presence of a D-amino acid

The primary structure of the neurohormone crustacean hyperglycemic hormone (CHH-II) was determined by means of enzymatic digestions, manual Edman degradation, and mass spectrometry. CHH-II is a 72 residue peptide (molecular mass 8388 Da), with six cysteines forming three disulfide bridges that connect residues 7-43, 23-39, and 26-52. The peptide has blocked N- and C-termini, and lacks tryptophan, histidine, and methionine. The CHH-I and CHH-II of Procambarus bouvieri have identical sequences and elicit levels of hyperglycemia that are not distinguishable. The difference between the two isomorphs consists in a posttranslational modification of a L-Phe in CHH-I to a D-Phe in CHH-II at the third position from the N-terminus.

Characterization of crustacean hyperglycemic hormone from the crayfish (Procambarus clarkii): multiplicity of molecular forms by stereoinversion and diverse functions

The complete amino acid sequence of two forms of crustacean hyperglycemic hormone (CHH) from the X-organ sinus gland complex of crayfish (Procambarus clarkii) has been determined. There are two variants of P. clarkii CHH (Prc-CHH), I and II, which can be separated by reversed-phase high-performance liquid chromatography (RP-HPLC). Each variant was oxidized by performic acid and then cleaved with lysyl endopeptidase. Intact hormone was also digested with trypsin and endoproteinase Asp-N, successively. The resulting fragments were separated by RP-HPLC and subjected to sequence analyses by a gas-phase sequencer and tandem mass spectrometry. Both variants contain 72 amino acid residues with three disulfide linkages, at positions 7-43, 23-39, and 26-52, and differ from each other by the D/L epimerization of phenylalanine at position 3; Prc-CHH-II contains D-amino acid. Injections of Prc-CHH-I and Prc-CHH-II at a dose of 12.5 pmol resulted in significant increase of hemolymph glucose levels in the crayfish. The hormones are also active in repressing ecdysteroid synthesis at concentrations of 250 mM (Prc-CHH-I) and 25 nM (Prc-CHH-II) in Y-organ culture. These results may indicate that the stereoinversion in the CHH molecule leads to an important alternation in hormonal functions during crustacean development.

The low molecular weight protein which co-purifies with alpha-latrotoxin is structurally related to crustacean hyperglycemic hormones

LMWP is the low molecular weight protein which copurifies with alpha-latrotoxin, the main neurotoxin from the black widow venom. It contains 70 residues and three disulfides. We found that its primary structure, including its 6 half-cystines, can be aligned with the amino acid sequences of crustacean hyperglycemic hormones (CHHs) which contain 72-73 residues and three disulfides. To further investigate this structural relationship, we produced a recombinant analog of LMWP in which the unique Met was changed in Leu (LMWPM35L). LMWPM35L was produced as a folded fusion protein in the periplasm of Escherichia coli and was generated in vitro by treating the fusion protein with cyanogen bromide. We showed that LMWPM35L and CHHs have an identical disulfide pairing pattern and possess some alpha-helical structure, as deduced from a comparison of their circular dichroism spectra. In addition, LMWPM35L and CHHs are consensually predicted to possess a helical structure within the region 13-17. Together, the data indicate that CHHs are structurally related to LMWPM35L and presumably also to LMWP. Finally, preliminary studies showed that LMWPM35L is not toxic to mice and does not form channels in lipid bilayers, two well-known properties of alpha-latrotoxin preparations.

Evidence for a conformational polymorphism of invertebrate neurohormones. D-amino acid residue in crustacean hyperglycemic peptides

Several large peptidic neurohormones have been isolated in crustaceans. In lobster and other related species, each of these neurohormones, and particularly the crustacean hyperglycemic hormone, occurs as two isoforms having the same peptidic sequence and molecular mass. We report here that these isoforms differ by the configuration of a single amino acid residue. The third residue (Phe3) of the lobster hyperglycemic hormones is in either the L- or D-configuration. In addition, we have shown that the biological activity of the two isoforms differs when considering the kinetics of their hyperglycemic effect.

Structure of the RGD protein decorsin: conserved motif and distinct function in leech proteins that affect blood clotting

The structure of the leech protein decorsin, a potent 39-residue antagonist of glycoprotein IIb-IIIa and inhibitor of platelet aggregation, was determined by nuclear magnetic resonance. In contrast to other disintegrins, the Arg-Gly-Asp (RGD)-containing region of decorsin is well defined. The three-dimensional structure of decorsin is similar to that of hirudin, an anticoagulant leech protein that potently inhibits thrombin. Amino acid sequence comparisons suggest that ornatin, another glycoprotein IIb-IIIa antagonist, and antistasin, a potent Factor Xa inhibitor and anticoagulant found in leeches, share the same structural motif. Although decorsin, hirudin, and antistasin all affect the blood clotting process and appear similar in structure, their mechanisms of action and epitopes important for binding to their respective targets are distinct.

Processing and targeting of a molluscan egg-laying peptide prohormone as revealed by mass spectrometric peptide fingerprinting and peptide sequencing

The neuroendocrine cerebral caudodorsal cells of Lymnaea stagnalis initiate and coordinate ovulation and egg mass production and associated behaviors through the release of a complex set of peptides that are derived from the caudodorsal cell hormone-I (CDCH-I) precursor. We have previously characterized the CDCH-I peptide. In the present study, we isolated and amino acid sequenced by conventional peptide chemistry five additional peptides, epsilon-peptide, calfluxin, alpha-caudodorsal cell peptide, delta-peptide, and carboxyl-terminally located peptide, from the cerebral commissure, the neurohemal area of the caudodorsal cells. Fingerprinting by matrix-assisted laser desorption mass spectrometry of peptides in the commissure demonstrated the presence of all sequenced peptides and, in addition, could identify two other peptides derived from pro-CDCH-1, the beta 1- and beta 3-peptides. These findings together with previous immunocytochemical studies enabled us to define cleavage sites and major processing events of pro-CDCH-1. Pro-CDCH-1 is initially cleaved in the Golgi apparatus into carboxyl- and amino-terminal parts, each of which is sorted into distinct vesicle classes that traffic to different intracellular sites. As a result, in the commissure, peptides derived from the carboxyl-terminal part, including CDCH-1, are present at a many-fold higher concentration than those derived from the amino-terminal part.

Isolation and characterization of hirustasin, an antistasin-type serine-proteinase inhibitor from the medical leech Hirudo medicinalis

Antistasin, a potent inhibitor of the blood coagulation factor Xa, is the prototype of a novel family of serine-proteinase inhibitors. We have now isolated, sequenced and characterized an antistasin-type inhibitor from the medical leech Hirudo medicinalis. Hirustasin (Hirudo antistasin) was purified to apparent homogeneity by cation-exchange and affinity chromatography. Amino acid sequencing of the 55 amino acid protein (M(r) 5866) revealed that hirustasin is the only antistasin-type protein known to consist of one domain only; 27% and 32% sequence identity was found to the first and second domains of antistasin, respectively, and a nearly exact conservation of the spacing of the ten cysteine residues. Hirustasin is the first inhibitor of tissue kallikrein identified in leeches, and is also a tight-binding inhibitor of trypsin, chymotrypsin and neutrophil cathepsin G. However, despite the high similarity to antistasin, particularly in the vicinity of the putative reactive-site peptide bond, hirustasin neither inhibits blood coagulation in vitro nor amidolytic activity of isolated factor Xa. Thus, structural elements other than the reactive site sequence significantly influence the specificity of antistasin-type proteinase inhibitors.

Annetocin: an oxytocin-related peptide isolated from the earthworm, Eisenia foetida

An oxytocin-vasopressin-related peptide, Cys-Phe-Val-Arg-Asn-Cys-Pro-Thr-Gly-NH2, was isolated from the lumbricid earthworm, Eisenia foetida and termed annectocin. Annetocin potentiated not only spontaneous contractions of the gut but also pulsatory contractions and bladder-shaking movement of the nephridia. Annetocin may be involved in osmoregulation of the animal through nephridial function.

Isolation, sequence, and bioactivity of FMRFamide-related peptides from the locust ventral nerve cord

The ventral nerve cord of the locust, Locusta migratoria, was examined for the presence of FMRFamide-related peptides (FaRPs). RP-HPLC coupled to an RIA specific for extended -RFamides revealed the presence of several FaRPs eluting at different percentages of acetonitrile. The sequences of five of these peptides were determined. Two sequences are identical to the two peptides previously sequenced from brain and retrocerebral complex of Locusta. These two peptides (PDVDHVFLRFamide and ADVGHVFLRFamide) were inhibitory when tested on locust oviduct contractions. The other peptides are novel with sequences of GQERNFLRFamide, AXXRNFIRFamide, and AFIRFamide. The synthesized peptides were stimulatory when tested on locust oviduct contractions, increasing the frequency and amplitude of spontaneous contractions and resulting in a basal contraction.

Determinants of potency and temperature-dependent function in the Aplysia bag cell peptides

Structure-activity relationships were determined for the natural bag cell peptides (BCPs) and for a series of synthetic analogues in terms of their ability to stimulate (at 30 degrees C) and to inhibit (at 15 degrees C) bag cell adenyl cyclase. We found that the core RLRF motif shared by all these peptides is active in this assay, and is stimulatory. The histidine residue C-terminal to this motif in beta-BCP is superfluous in this respect. An electronegative residue C-terminal to RLRF is sufficient to induce temperature-dependent function. The Ala-Pro pair that is N-terminal to this motif in alpha-BCP increases potency, but does not alter function.

Purification and characterization of Aplysia atrial gland secretory granules containing egg-laying prohormone-related peptides

A purification scheme is described for the isolation of secretory granules containing egg-laying prohormone-related peptides from the atrial gland of Aplysia californica, an exocrine organ in the reproductive tract. Granules were purified by differential centrifugation of atrial gland homogenates followed by centrifugation on continuous Percoll-sucrose gradients. Quantitative enzyme assays in conjunction with electron microscopic analyses demonstrated that secretory granules thus isolated were significantly purified with respect to other subcellular organelles such as mitochondria and lysosomes. Immunoelectron microscopy demonstrated that the majority (approximately 85%) of the purified secretory granules were immunoreactive for A-NTP (N-terminal peptide), a cleavage product of the egg-laying prohormone-related A and A' precursors (residues 22-34). The purified granules represented an enriched source of peptides that were readily resolved by reversed-phase high performance liquid chromatography.

Molecular cloning of crustacean putative molt-inhibiting hormone (MIH) precursor

A cDNA encoding the complete precursor of the putative molt-inhibiting hormone (MIH) of the shore crab, Carcinus maenas, was isolated and sequenced. The precursor consists of a putative 35 amino acid signal peptide and the 78 amino acid mature MIH. The deduced MIH amino acid sequence is in complete agreement with the sequence previously determined by Edman degradation. In situ hybridization revealed MIH-expression in a subpopulation of large neurosecretory perikarya of the medulla terminalis X-organ in the eyestalk.

Crystal structure of an endotoxin-neutralizing protein from the horseshoe crab, Limulus anti-LPS factor, at 1.5 A resolution

Lipopolysaccharide (LPS), or endotoxin, is the major mediator of septic shock, a serious complication of Gram-negative bacterial infections in humans. Molecules that bind LPS and neutralize its biological effects or enhance its clearance could have important clinical applications. Limulus anti-LPS factor (LALF) binds LPS tightly, and, in animal models, reduces mortality when administered before or after LPS challenge or bacterial infection. Here we present the high resolution structure of a recombinant LALF. It has a single domain consisting of three alpha-helices packed against a four-stranded beta-sheet. The wedge-shaped molecule has a striking charge distribution and amphipathicity that suggest how it can insert into membranes. The binding site for LPS probably involves an extended amphipathic loop, and we propose that two mammalian LPS-binding proteins will have a similar loop. The amphipathic loop structure may be used in the design of molecules with therapeutic properties against septic shock.

Lipopolysaccharide detoxification by endotoxin neutralizing protein

Endotoxin neutralizing protein (ENP), a recombinant form of the anti-lipopolysaccharide factor that was isolated from amebocytes of the American horseshoe crab, Limulus polyphemus, detoxifies lipopolysaccharide (LPS) both in vitro and in vivo. Using the Limulus amebocyte lysate assay, LPS was detoxified by ENP at a 1 to 1 weight ratio (1:1). When isolated rat aortic rings were preincubated for 16 hr with either LPS or LPS/ENP (1:5), only aortas in the LPS/ENP group contracted normally under norepinephrine stimulation. To show that detoxification of a lethal amount of LPS (18 mg/kg, LD50 at 48 hr) persists in vivo, LPS/albumin (1:1) or LPS/ENP (1:1) mixtures were preincubated (30 min, 37 degrees C) and then injected intravenously into rats. In the 8 hr after injection, LPS/ENP challenged rats, in contrast to their LPS/albumin injected counterparts, had significantly fewer physical signs of acute LPS toxicity (P < 0.001). At 48 hr after challenge, all LPS/ENP treated rats survived (P < 0.01 vs LPS/albumin), and with significantly less weight loss (P < 0.001 vs LPS/albumin challenged survivors). At necropsy, the LPS/ENP group was free of typical LPS-induced gross organ lesions, notably in the liver, spleen, gut-associated lymphoid tissue (GALT), and small intestine. By microscopic examination, lymphocytic necrosis in the spleen and GALT of the LPS/ENP treated survivors was significantly milder than that in the LPS/albumin challenged survivors, although the degree of hepatocellular necrosis and small intestinal enteritis was similar. LPS-neutralizing proteins such as ENP may be useful in treating LPS toxicity.

GNFFRFamide: a novel FMRFamide-immunoreactive peptide isolated from the sheep tapeworm, Moniezia expansa

The widespread distribution of FMRFamide-immunoreactivity in platyhelminth nervous systems has been demonstrated immunocytochemically. Here we report the isolation and primary structure of the first platyhelminth FMRFamide-related peptide (FaRP) from the tapeworm, Moniezia expansa. The peptide was found to have a molecular mass of 785 Da and a primary structure of Gly-Asn-Phe-Phe-Arg- Phe-NH2 (GNFFRFamide). Acid alcohol extracts of this platyhelminth contained only this single FaRP which had a phenylalanyl (F) residue in the variable position 3 from the C-terminal occupied by either methionyl (M), leucyl (L) or isoleucyl (I) residues in most other FaRPs.

Crystallization and preliminary crystallographic analysis of antistasin, a leech-derived inhibitor of blood coagulation factor Xa

The salivary gland of the Mexican leech Haementeria officinalis contains a 15 kDa protein which is a potent and selective inhibitor of factor Xa. It inhibits not only blood coagulation, but also metastasis. A gene, coding for a sequence similar to published antistasin sequences, has been synthesized and expressed in Chinese hamster ovary (CHO) cells. The recombinant protein was purified and crystallized at pH 6.0, using 31% ammonium sulfate as a precipitant. The crystals diffract at least to 2.8 A. The spacegroup is I422 with a = b = 77.7 A and c = 88.4 A. The crystals contain 42% solvent and one protein molecule in the asymmetric unit. A search for heavy atom derivatives is in progress.

The complete amino acid sequence of a hirudin variant from the leech Hirudinaria manillensis

Unlike the European leech Hirudo medicinalis, the Asian jawed leech Hirudinaria manillensis is specialized for feeding on mammalian blood. In the salivary glands of both these leeches, there is a potent inhibitor of thrombin, called hirudin, which acts as an anticoagulant. We have reported previously the isolation and purification of a variant of hirudin, called bufrudin, from the head portions of Hirudinaria. In the present study, the complete amino acid sequence of bufrudin was determined by automated Edman degradation of peptide fragments generated after cleavage of protein with trypsin or thermolysin. Comparison of the primary structure of bufrudin, with hirudin HV1, show about 70% sequence identity with deletion of two amino acids, but the key amino acids at the C-terminus, involved in the inhibition of thrombin, are conserved. However, similar sequence comparison of bufrudin with hirullin P18, a hirudin variant isolated from the same leech species but from whole leech, instead of heads, reveals even less sequence identity of about 60%. From the amino acid sequence, it is suggested that the conformation of the C-terminal portion of bufrudin may be significantly different from hirullin P18, but similar to hirudin HV1, upon its interaction with thrombin. These results indicate that, as with Hirudo leech, various isoforms of hirudin also exist in Hirudinaria leech, with a significant change occurring in the structure of the molecule during the evolution of leeches.

Structure and sequence relationships in the lipocalins and related proteins

The lipocalins and fatty acid-binding proteins (FABPs) are two recently identified protein families that both function by binding small hydrophobic molecules. We have sought to clarify relationships within and between these two groups through an analysis of both structure and sequence. Within a similar overall folding pattern, we find large parts of the lipocalin and FABP structures to be quantitatively equivalent. The three largest structurally conserved regions within the lipocalin common core correspond to characteristic sequence motifs that we have used to determine the constitution of this family using an iterative sequence analysis procedure. This afforded a new interpretation of the family, which highlighted the difficulties of determining a comprehensive and coherent classification of the lipocalins. The first of the three conserved sequence motifs is also common to the FABPs and corresponds to a conserved structural element characteristic of both families. Similarities of structure and sequence within the two families suggests that they form part of a larger "structural superfamily"; we have christened this overall group the calycins to reflect the cup-shaped structure of its members.

Isolation, sequence analysis, and cloning of haemadin. An anticoagulant peptide from the Indian leech

A slow, tight-binding inhibitor of thrombin with an apparent molecular mass of about 5 kDa has been isolated from Haemadipsa sylvestris, an Indian leech of the family of Haemadipsidae. The inhibitory activity, called haemadin, is thrombin specific since it does not inhibit other proteases like trypsin, chymotrypsin, factor Xa, or plasmin. NH2-terminal amino acid sequence analysis (residues 1-45) does not reveal any homology to known serine protease inhibitors, including the thrombin-specific inhibitor hirudin. The haemadin cDNA cloned by polymerase chain reaction techniques codes for a polypeptide of 57 amino acid residues preceded by 20 residues of a signal peptide sequence. A synthetic gene coding for the mature haemadin was expressed in Escherichia coli. Recombinant haemadin displays a similar inhibition constant and specific activity as its natural counterpart. Although there is no obvious sequence identity between haemadin and hirudin, both proteins seem to share common mechanisms for thrombin inhibition.

Isolation and molecular characterization of a hyperglycemic neuropeptide from the sinus gland of the terrestrial isopod Armadillidium vulgare (Crustacea)

The major peptide from the sinus gland of the terrestrial isopod Armadillidium vulgare (Crustacea) has been extracted and purified by reverse-phase HPLC. This neuropeptide exhibited a high hyperglycemic activity and was therefore named A. vulgare crustacean hyperglycemic hormone (Arv-CHH). Its average molecular mass measured by mass spectrometry was 8729.3 Da. Its complete amino acid sequence was determined by a combination of Edman degradation and mass spectrometry. The N-terminal amino acid was found to be unblocked, the C-terminal residue was found amidated and none of the other 72 residues was affected by any post-translational modification. Disulfide bond assignment was made unambiguously by mass spectrometry and Edman degradation was performed on peptides produced by enzymatic cleavage. Relationships with other, similar neuropeptides from decapod sinus glands are discussed.

Primary structure of the major isomorph of the crustacean hyperglycemic hormone (CHH-I) from the sinus gland of the Mexican crayfish Procambarus bouvieri (Ortmann): interspecies comparison

The amino acid sequence of this neuropeptide was elucidated by means of a combined approach of enzymatic digestions, manual and automatic Edman degradations, and mass spectrometry. It is a 72 residue peptide (molecular mass 8388 Da), with six cysteines forming three disulfide bridges connecting residues 7-43, 23-39, and 26-52, with blocked N- and C-termini, and lacking the amino acids histidine, methionine, and tryptophan. The CHH-I of Procambarus bouvieri is compared with the other known CHHs from Orconectes limosus (98.6% identity), Homarus americanus isomorph A (83.3% identity), Homarus americanus isomorph B (79.2% identity), and Carcinus maenas (61.1% identity).

Early steps in ecdysteroid biosynthesis: evidence for the involvement of cytochrome P-450 enzymes

The first step in the biosynthesis of ecdysteroids by Manduca sexta prothoracic glands, the conversion of cholesterol to 7-dehydrocholesterol, is mediated by an enzyme with characteristics of a microsomal cytochrome P-450, i.e. sensitivity to CO and fenarimol, and a requirement for NADPH. The enzyme responsible for hydroxylation at C-25 of the putative 3-dehydroecdysone precursor, 14-hydroxy-5 beta-cholest-7-en-3,6-dione, is also microsomal, while those mediating hydroxylations at C-22 and C-2 of 3,14,25-trihydroxy-5 beta-cholest-7-en-6-one are mitochondrial. Indirect evidence revealed that the steps between 7-dehydrocholesterol and the trideoxyecdysteroids occur in the mitochondria, suggesting that extensive shuttling of intermediates between the endoplasmic reticulum and mitochondria takes place in the prothoracic gland cell during ecdysteroid biosynthesis. During the fifth larval instar, cholesterol 7,8-dehydrogenase activity is evident from days 2 to 9, while the conversion to [3H]ecdysteroids is not significant prior to the ecdysteroid commitment peak on day 4. Terminal hydroxylase activity shows little change throughout the instar. These data support the hypothesis that regulation of the biosynthetic pathway by PTTH occurs at the step immediately following the formation of 7-dehydrocholesterol. The steroid biosynthesis inhibitor, fenarimol, has been shown to inhibit each of these P-450 enzymes, as well as fat body ecdysone 20-monooxygenase, with an I50 of 10(-4) M in disrupted glands, suggesting that it is a general P-450 inhibitor. The secretion of ecdysteroids by the glands in vitro is very sensitive to fenarimol, i.e. I50 of 10(-6) M. RH5849, 1,2-dibenzoyl-1-tert-butylhydrazine, fails to inhibit any of these prothoracic gland reactions, yet strongly inhibits fat body ecdysone 20-monooxygenase activity. This suggests that RH5849 is a specific ecdysteroid substrate/product mimic in this reaction.

Effect of the D-Phe2 residue on molecular conformation of an endogenous neuropeptide achatin-I. Comparison of X-ray crystal structures of achatin-I (H-Gly-D-Phe-Ala-Asp-OH) and achatin-II (H-Gly-Phe-Ala-Asp-OH)

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 beta-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.