P-Conotoxins

Although it is a general rule to operate at high dilution (10-4-10 5M) in oxidative folding reactions to avoid formation of intermolecular disulfide-bonded species, p.-conotoxin GIIIB offers an opposite example (Scheme 10). This toxin belongs to a family of conotoxins from marine snails consisting of 22 amino add residues with three intramolecular disulfide bonds.185 ... 

When air oxidation of the reduced p-conotoxin GIIIB (18) was carried out in 0.1 M NHtOAc buffer (pH 7.5) at 0.01 mM peptide concentration and at 10 °C, three major products, isomers 15,16, and 17 were produced after 40 hours in a ratio of 1 4 3 (Figure 2). 86 The disulfide structures of each isomer were determined by enzymatic digestion followed by amino acid analyses, mass spectrometry, sequence analyses, as well as by the synthetic approach (Scheme 10). 

Table 1 Eight Possible Lysyl Endopeptidase Fragments of p-Conotoxin GIIIB with Different Disulfide Connectivities and Ratios of (PTH-Cys)2 during Their Sequencing 72 "...

Piscidin 1 and its analogues Piscidin 1 and its analogues PIIIA toxin Tetrodotoxin-resistant Na+ channel binding by p-conotoxin smlllA C. purpurascens Conus stercusmuscarum... 

The Nayl a-subunit is a large protein, and several receptor sites for natural product neurotoxins have been identified by photoaffinity labeling and site-directed mutagenesis [79]. The small hydrophilic guanidines TTX and STX and the p,-conotoxin peptides bind at the extracellular mouth of the conduction pathway and are thought to physically occlude the pore. Binding of these toxins shows little state- or use-dependence. A number of a scorpion, sea anemone, and spider toxins also bind to an extracellular site, but act as... 

Geocillin carindacillin. geographutoxin I p-conotoxin GIIIA. geographutoxin II p-conotoxin GIIIB. 

Na l.4 SCN4A 17q23-25 Naypi Skeletal muscle TTX (10 nM), STX (2 nM), p-conotoxin GIIIA, p-conotoxin PIIIA, local anesthedc, antiepileptic, andarrhythymic drugs... 

Na+ 1,11.Ill,Ml,111 voltage-gated depolari sal ion tetrodotoxin saxitoxin p-conotoxin... 

Preclinical evidence suggests selective Nay 1.8 inhibitors may provide relief from inflammatory pain conditions without mechanism-based cardiac and CNS side effects. To date, this hypothesis has been validated in rodent models of pain using targeted genetic disruption (Akopian et al. 1999 Laird et al. 2002), antisense oligonucleotide-mediated depletion (Villarreal et al. 2005), a p-conotoxin less than tenfold selective for Nayl.8 over other sodium channels (Ekberg et al. 2006), and, most recently, a small molecule with nanomolar potency and more than 100-fold selectivity over other sodium channels (Jarvis et al. 2007). 

This combination of toxins lead to hyperactivity of the fish, followed by a continuous contraction and extension of major hns, without death. The second phase consists in a flaccid state and is caused by a different cocktail of neurotoxins (see Table 5.1) the a-conotoxins that block nicotinic acetylcholine receptors the p-conotoxins that block voltage-dependent Na channels the /-conotoxins that also block nicotinic acetylcholine receptors the K-conotoxins that cause the blockade of K channels the 5-conotoxins that suppress the inactivation of the voltage-dependent Na channels, and the co-conotoxins that block voltage-dependent Ca channels, and are the snbject of this chapter. 

French, R.J., Yoshikami, D., Sheets, M.F., and Olivera, B.M. (2010) The tetrodotoxin receptor of voltage-gated sodium channels-perspectives from interactions with p-conotoxins. Mar. Drugs, 8, 2153-2161. 

Aguilar, M.B., Chan de la Rosa, R.A., Falcon, A., Olivera, B.M., and Heimer de la Cotera, E.P. (2009b) Peptide pal9a from the venom of the turrid snail Polystira albida from the Gulf of Mexico Purification, characterization, and comparison with P-conotoxin-like (framework IX) conoidean peptides. Peptides, 30, 467-476. 

Close to 90% of the naturally-occurring Conus peptides have four to six cysteine residues involved in disulfide bonds. Most of the peptides found so far belong to the three structural classes (see Table 1) corresponding to different arrangements of cysteine residues. The most abundant structural class appears to be the 6-Cys/4-loop cysteine framework typified by the co-conotoxins (C—C—CC—C—C), followed by the 6-Cys/3-loop framework represented by p-conotoxins (CC—C—C—CC), and the 4-Cys/2-loop framework of the a-conotoxins (CC—C—C). This structural motif, i.e., the presence of multiple disulfide bonds, is responsible for maintaining many Conus peptides in a fairly rigid and compact conformation needed for the rapid transport of the peptides to their macromolecular targets. 

Conotoxin-GS, a sodium channel blocker isolated from C. geographus, has the 6-Cys/4-loop framework (C—C—CC—-C—C) of co-conotoxins rather than the 6-Cys/3-loop arrangement (CC—C—C—CC) of the p-conotoxins, the major Na channel blocker from C. geographus (Yanagawa et al., 1988). Conotoxin-GS also has the conserved Gly residue in the first loop typical of co-conotoxins. In fact, Yanagawa and co-workers have pointed out the greater sequence similarity of conotoxin-GS to the calcium channel blocker co-conotoxin MVIIA than to the p-conotoxin GUI series. Although the affinity of conotoxin-GS to sodium channels is much less than that of p-conotoxins, conotoxin-GS was also found to preferentially bind to Site I of the muscle rather than the neuronal subtype of sodium channels. 

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