Structural and functional studies of small, disulfide-rich peptides depend on their efficient chemical synthesis and folding. A large group of peptides derived from animals and plants contains the Cys pattern: C-C-CC-C-C that forms the inhibitory cystine knot (ICK) or knottin motif. Here we report the effect of site-specific incorporation of pairs of selenocysteine residues on oxidative folding and the functional activity of ω-conotoxin GVIA, a well-characterized ICK-motif peptidic antagonist of voltage-gated calcium channels. Three selenoconotoxin GVIA analogs were chemically synthesized; all three folded significantly faster in the glutathione-based buffer compared to wildtype GVIA. One analog, GVIA[C8U,C19U], exhibited significantly higher folding yields. A recently described NMR-based method was used for mapping the disulfide connectivities in the three selenoconotoxin analogs. The diselenide-directed oxidative folding of selenoconotoxins was predominantly driven by amino acid residue loop sizes formed by the resulting diselenide and disulfide crosslinks. Both in vivo and in vitro activities of the analogs were assessed; block of N-type calcium channels was comparable among the analogs and wild-type GVIA, suggesting that the diselenide replacement did not affect the bioactive conformation. Thus, diselenide substitution may facilitate oxidative folding of pharmacologically diverse ICK peptides. The diselenide replacement has been successfully applied to a growing number of bioactive peptides, including α-, µ-and ω-conotoxins, suggesting that the integrated oxidative folding of selenopeptides described here may prove to be a general approach for efficient synthesis of diverse classes of disulfide-rich peptides.Multiple disulfide cross-links are a major structural feature of many secreted polypeptides (1-3). If a secreted polypeptide is injected or meant to act on another organism (as is the case for animal venom components), it is subject to an additional selective pressure: to make the polypeptide smaller for rapid dissemination through the targeted animal's body. There is likely * This work was supported by the NIH program project PO1 GM-49677. The electrophysiology was supported by a grant from the Pennsylvania (PA) Department of Health using Tobacco Settlement Funds.Address Correspondence to: Grzegorz Bulaj, 421 Wakara Way, Suite 360, Department of Medicinal Chemistry, University of Utah, Salt Lake City, Utah 84108; phone (801) 581-4629, fax (801) 581-7087, bulaj@pharm.utah.edu. SUPPORTING INFORMATION AVAILABLEOne table (summary of KNOTTIN database analysis for three disulfide containing ICK peptides) and three supplemental figures ( Figure S1 -HPLC and mass spectrometry analysis of the linear form of GVIA[C8U,C19U]; Figure S2 -high resolution mass spectrometry analysis of the folded species of GIVA[C1U,C16U]; and Figure S3 -folding kinetics of GVIA and Sec-GVIA analogues in presence of 8 M urea) are provided as a supporting information. This material is available free of charge via the Internet a...

Described herein is a general approach to identify novel compounds using the biodiversity of a megadiverse group of animals; specifically, the phylogenetic lineage of the venomous gastropods that belong to the genus Conus ("cone snails"). Cone snail biodiversity was exploited to identify three new μ-conotoxins, BuIIIA, BuIIIB and BuIIIC, encoded by the fish-hunting species Conus bullatus. BuIIIA, BuIIIB and BuIIIC are strikingly divergent in their amino acid composition compared to previous μ-conotoxins known to target the voltage-gated Na channel skeletal muscle subtype Na v 1.4. Our preliminary results indicate that BuIIIB and BuIIIC are potent inhibitors of Na v 1.4 (average block ~96%, at a 1 μM concentration of peptide), displaying a very slow off-rate not seen in previously characterized μ-conotoxins that block Na v 1.4. In addition, the three new Conus bullatus μ-conopeptides help to define a new branch of the M-superfamily of conotoxins, namely M-5. The exogene strategy used to discover these Na channel-inhibiting peptides was based on both understanding the phylogeny of Conus, as well as the molecular genetics of venom μ-conotoxin peptides previously shown to generally target voltage-gated Na channels. The discovery of BuIIIA, BuIIIB and BuIIIC Na channel blockers expands the diversity of ligands useful in determining the structure-activity relationship of voltage-gated sodium channels.

Despite the therapeutic promise of disulfide-rich, peptidic natural products, their discovery and structure/function studies have been hampered by inefficient oxidative folding methods for their synthesis. Here we report that converting the three disulfide-bridged μ-conopeptide KIIIA into a disulfide-depleted selenoconopeptide (by removal of a noncritical disulfide bridge and substitution of a disulfide- with a diselenide-bridge) dramatically simplified its oxidative folding while preserving the peptide’s ability to block voltage-gated sodium channels. The simplicity of synthesizing disulfide-depleted selenopeptide analogs containing a single disulfide bridge allowed rapid positional scanning at Lys7 of μ-KIIIA, resulting in the identification of K7L as a mutation that improved the peptide’s selectivity in blocking a neuronal (Nav1.2) over a muscle (Nav1.4) subtype of sodium channel. The disulfide-depleted selenopeptide strategy offers regioselective folding compatible with high throughput chemical synthesis and on-resin oxidation methods, and thus shows great promise to accelerate the use of disulfide-rich peptides as research tools and drugs.

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T-1-family conotoxins belong to the T-superfamily and are composed of 10−17 amino acids. They share a common cysteine framework and disulfide connectivity, and exhibit unusual posttranslational modifications, such as tryptophan bromination, glutamic acid carboxylation and threonine glycosylation. We have isolated and characterized a novel peptide, Mo1274, containing 11 amino acids, that shows the same cysteine pattern, -CC-CC, and disulfide linkage as those of the T-1-family members. The complete sequence, GNWCCSARVCC, in which W denotes bromotryptophan, was derived from MS-based de novo sequencing. The FT-ICR MS/MS techniques of electron capture dissociation (ECD), infrared multiphoton dissociation (IRMPD), and collision-induced dissociation (CID) served to detect and localize the tryptophan bromination. The bromine contributes a distinctive isotopic distribution in all fragments that contain bromotryptophan. ECD fragmentation results in the loss of bromine and return to the normal isotopic distribution. Disulfide connectivity of Mo1274, between cysteine pairs 1−3 and 2−4, was determined by mass spectrometry in combination with chemical derivatization employing tris(2-carboxyethyl) phosphine, followed by differential alkylation with N-ethylmaleimide and iodoacetamide. The ECD spectra of the native and partially modified peptide reveal a loss of bromine in a process that requires the presence of a disulfide bond.