Predictive methods, physicochemical measurements, and structure activity relationship studies suggest that corticotropin-releasing factor (CRF; corticoliberin), its family members, and competitive antagonists (resulting from N-terminal deletions) usually assume an a-helical conformation when interacting with the CRF receptor(s). To test this hypothesis further, we have scanned the whole sequence of the CRF antagonist Nle21'38]r/hCRF-(12-41) (r/hCRF, rat/human CRF; Nle, norleucine) with an i-(i + 3) bridge consisting of the Giu-Xaa-Xa:-Lys scaffold. We have found astressin {cyclo (30)(31)(32)(33) Nle2l,38,Glu30,Lys33] Corticotropin-releasing factor (CRF; corticoliberin) is a 41-residue peptide amide which stimulates the release of corticotropin (ACTH) (1, 2) and acts within the brain to mediate a wide range of stress responses (3). The actions of CRF are mediated through binding to CRF receptors, several of which have been characterized recently (4-10). These receptors, like those for growth hormone-releasing factor, calcitonin, and vasoactive intestinal peptide, are coupled via G proteins and have seven putative transmembrane domains. The actions of CRF can also be modulated by a 37-kDa CRF-binding protein (CRF-BP) (11). To probe the physiological role of CRF, we have developed competitive antagonists that are particularly potent when administered in the central nervous system; however, these same analogs bind pituitary receptors with lower affinity than does CRF, and their peripheral administration results in weak and short-lived effects in vivo (12). Synthetic CRF antagonists such as the a-helical CRF-(9-41)

We have purified contulakin-G, a 16-amino acid Olinked glycopeptide (pGlu-Ser-Glu-Glu-Gly-Gly-SerAsn-Ala-Thr-Lys-Lys-Pro-Tyr-Ile-Leu-OH, pGlu is pyroglutamate) from Conus geographus venom. The major glycosylated form of contulakin-G was found to incorporate the disaccharide ␤-D-Galp-(133)-␣-D-GalpNAc-(13) attached to Thr 10 . The C-terminal sequence of contulakin-G shows a high degree of similarity to the neurotensin family of peptides. Synthetic peptide replicates of Gal(␤33) GalNAc(␣3)Thr 10 contulakin-G and its nonglycosylated analog were prepared using an Fmoc (9-fluorenylmethoxycarbonyl) protected solid phase synthesis strategy. The synthetic glycosylated contulakin-G, when administered intracerebroventricular into mice, was found to result in motor control-associated dysfunction observed for the native peptide. Contulakín-G was found to be active at 10-fold lower doses than the nonglycosylated Thr 10 contulakin-G analog. The binding affinities of contulakin-G and the nonglycosylated Thr 10 contulakin-G for a number of neurotensin receptor types including the human neurotensin type 1 receptor (hNTR1), the rat neurotensin type 1 and type 2 receptors, and the mouse neurotensin type 3 receptor were determined. The binding affinity of the nonglycosylated Thr 10 contulakin-G was approximately an order of magnitude lower than that of neurotensin [1][2][3][4][5][6][7][8][9][10][11][12][13] for all the receptor types tested. In contrast, the glycosylated form of contulakin-G exhibited significantly weaker binding affinity for all of the receptors tested. However, both contulakin-G and nonglycosylated Thr 10 contulakin-G were found to be potent agonists of rat neurotensin receptor type 1. Based on these results, we conclude that O-linked glycosylation appears to be a highly unusual strategy for increasing the efficacy of toxins directed against neurotransmitter receptors.

Most vertebrate species have more than one form of gonadotropin-releasing hormone (GnRH) in their brains, but it is not clear whether each form has a distinct function. We report that sea bream (Sparus awrta) brains have three forms of GnRH, one of which is described herein and is called sea bream GnRH (sbGnRH). The primary structures of two forms were determined by Edman degradation and mass spectral analysis. The amino acid sequence of sbGnRH is pGlu-His-Trp-Ser-Tyr-Gly-Leu-Ser-Pro-Gly-NH2. The second peptide is identical to a form originally isolated from chicken brains (cGnRH-II): pGlu-His-Trp-Ser-His-Gly-Trp-Tyr-ProGly-NH2. cGnRH-H is the most ancient form of GnRH identified to date in jawed fish and the most prevalent form throughout the vertebrates. The third form of GnRH has previously been identified as salmon GnRH by cDNA studies and is confirmed here by chromatographic and immunological studies. Phylogenetic distribution of GnRH peptides suggests sbGnRH arose in the perch-like fish as a gene duplication of the existing cGnRH-ll or salmon GnRH genes. All three identified GnRH peptides were synthesized and shown to release gonadotropin in vivo in the sea bream. The dominant form of GnRH stored in the pituitary was sbGnRH. Not only was the content ofsbGnRH 500-fold greater than that ofsalmon GnRH but also cGRH-II was not deeced in the pituitary. The latter evidence suggests that sbGnRH is the endogenous releaser of gonadotropin II.Gonadotropin-releasing hormone (GnRH) is both a releaser of gonadotropins and a neuromodulator (1, 2)

Corticotropin releasing factor (CRF), 1 a 41-amino acid peptide, was identified initially on the basis of its primary role in the activation of the hypothalamic-pituitary-adrenal in response to stress. The CRF family of ligands includes sauvagine from frog and urotensin from fish as well as the additional mammalian family members, urocortin (1, 2), urocortin II (3, 4), and urocortin III (4, 5). Broader roles for CRF and its ligand family now involve effects on the cardiovascular, reproductive, gastrointestinal, immune, and central nervous systems (6 -8).The action of CRF and related ligands is initiated by binding to their receptors, which transduce an increase in intracellular cAMP. Thus far, two receptors, CRFR1 and CRFR2, have been cloned in mammals (9 -15). Homologous receptors have been identified in chicken (16), fish (17), and Xenopus (18) and a third receptor, CRFR3, with high levels of sequence identity to CRFR1, has recently been cloned in catfish (17). Both CRFR1 and CRFR2 exist as multiple splice variants and belong to the type B 7-transmembrane receptor family that includes receptors for growth hormone releasing factor, secretin, calcitonin, vasoactive intestinal peptide, glucagon, glucagon-like peptide, and parathyroid hormone (PTH). Receptors for the CRF ligand family have been characterized in the central nervous system, pituitary, gastrointestinal tract, epididymis, heart, gonads, and adrenals (6).The affinities of CRF and urocortin in binding to CRFR1 are nearly the same but in binding to CRFR2, urocortin is ϳ10 times more potent than CRF (19). Both urocortins II and III are highly selective in binding and activating CRFR2 compared with CRFR1 (4, 5). A synthetic peptide antagonist, astressin, binds with equally high affinity to CRFR1 and CRFR2 (19,20).The CRF receptor family consists of proteins with a relatively large first extracellular domain (ECD-1). Mutagenesis studies have identified regions of the CRF receptors that are implicated in differential recognition of agonists and antagonists, as well as in governing the ligand selectivity of the two types of receptors (21-25). We showed that a chimeric receptor in which the ECD-1 of CRFR1 replaced the ECD of the activin receptor, a single transmembrane receptor kinase (26), was capable of high affinity binding to both astressin and urocortin (21). The mode of receptor activation was explored by our study of a tethered peptide-receptor chimera in which the first 16 amino acids of CRF were substituted for the ECD-1 of CRFR1 (CRF (1-16)/R1 ⌬N ) (27). This chimera displayed continual signaling suggesting that the N-terminal third of CRF, when presented in proximity to the receptor, is able to cause activation.Biochemical characterizations of soluble ECD-1s include those of receptors for follicle stimulating hormone (28), luteinizing hormone/human chorionic gonadotropin (29), calcium (30), PTH (31), glucagon-like peptide-1 (32), and glutamate (33). The ECD-1 of the metabotropic glutamate receptor has

Predatory cone snails (genus Conus) comprise what is arguably the largest living genus of marine animals (500 species). All Conus use complex venoms to capture prey and for other biological purposes. Most biologically active components of these venoms are small disulfide-rich peptides, generally 7±35 amino acids in length. There are probably of the order of 100 different peptides expressed in the venom of each of the 500 Conus species [1,2]. Peptide sequences diverge rapidly between Conus species, resulting in a distinct peptide complement for each species. Thus, the genus as a whole has probably generated < 50 000 different peptides, which can be organized into families and superfamilies with shared sequence elements [3]. In this minireview, we provide a brief overview of the neuropharmacological, molecular and cell-biological aspects of the Conus peptides. However, the major focus of the review will be the remarkable array of post-translational modifications found in these peptides.