title: SNX-325, a novel calcium antagonist from the spider Segestria florentina.
abstract: A novel selective calcium channel antagonist peptide, SNX-325, has been isolated from the venom of the spider Segestria florentina. The peptide was isolated using as bioassays the displacement of radioiodinated omega-conopeptide SNX-230 (MVIIC) from rat brain synaptosomal membranes, as well as the inhibition of the barium current through cloned expressed calcium channels in oocytes. The primary sequence of SNX-325 is GSCIESGKSCTHSRSMKNGLCCPKSRCNCRQIQHRHDYLGKRKYSCRCS, which is a novel amino acid sequence. Solid-phase synthesis resulted in a peptide that is chromatographically identical with the native peptide and which has the same configuration of cysteine residues as the spider venom peptide omega-Aga-IVa [Mintz, I. M., et al., (1992) Nature 355, 827-829]. At micromolar concentrations, SNX-325 is an inhibitor of most calcium, but not sodium or potassium, currents. At nanomolar concentrations, SNX-325 is a selective blocker of the cloned expressed class B (N-type), but not class C (cardiac L), A, or E, calcium channels. SNX-325 is approximately equipotent with the N-channel selective omega-conopeptides (GVIA and MVIIA as well as closely related synthetic derivatives) in blocking the potassium induced release of tritiated norepinephrine from hippocampal slices (IC50s, 0.1-0.5 nM) and in blocking the barium current through cloned expressed N-channels in oocytes (IC50s 3-30 nM). By contrast, SNX-325 is 4-5 orders of magnitude less potent than is SNX-111 (synthetic MVIIA) at displacing radioiodinated SNX-111 from rat brain synaptosomal membranes. SNX-325 will be a useful comparative tool in further defining the function and pharmacology of the N- and possibly other types of high-voltage activated calcium channels.
authors.affiliation: Neurex Corporation, Menlo Park, California 94025-1012, USA.
authors.forename: R
authors.initials: R
authors.lastname: Newcomb
authors.forename: A
authors.initials: A
authors.lastname: Palma
authors.forename: J
authors.initials: J
authors.lastname: Fox
authors.forename: S
authors.initials: S
authors.lastname: Gaur
authors.forename: K
authors.initials: K
authors.lastname: Lau
authors.forename: D
authors.initials: D
authors.lastname: Chung
authors.forename: R
authors.initials: R
authors.lastname: Cong
authors.forename: J R
authors.initials: JR
authors.lastname: Bell
authors.forename: B
authors.initials: B
authors.lastname: Horne
authors.forename: L
authors.initials: L
authors.lastname: Nadasdi
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001667:Binding, Competitive; D001921:Brain / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000737:chemistry* / Q000302:isolation & purification; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D002268:Carboxypeptidases; D043402:Cathepsin A; D002918:Chymotrypsin; D005260:Female; D007457:Iodine Radioisotopes; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology; D008969:Molecular Sequence Data; D009865:Oocytes / Q000187:drug effects / Q000502:physiology; D009928:Organ Specificity; D010446:Peptide Fragments / Q000737:chemistry / Q000302:isolation & purification; D010455:Peptides / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism / Q000494:pharmacology; D051381:Rats; D017386:Sequence Homology, Amino Acid; D013111:Spider Venoms; D013112:Spiders; D013574:Synaptosomes / Q000378:metabolism; D014981:Xenopus; D020960:omega-Conotoxins
chemical_list: D002121:Calcium Channel Blockers; D015220:Calcium Channels; D007457:Iodine Radioisotopes; D007473:Ion Channels; D010446:Peptide Fragments; D010455:Peptides; C094484:SNX 325; D013111:Spider Venoms; D020960:omega-Conotoxins; C075851:omega-conotoxin-MVIIC; D002268:Carboxypeptidases; D043402:Cathepsin A; D002918:Chymotrypsin