Efficient oxidative folding of conotoxins and the radiation of venomous cone snails

doi:10.1073/pnas.2335845100

Efficient oxidative folding of conotoxins and the radiation of venomous cone snails

^*Department of Biology, University of Utah, Salt Lake City, UT 84112; ^†Cognetix, Inc., 421 Wakara Way, Salt Lake City, UT 84108; and ^‡Department of Physical Sciences, College of Science, University of the Philippines Baguio, Baguio City, Philippines

Abstract

The 500 different species of venomous cone snails (genus Conus) use small, highly structured peptides (conotoxins) for interacting with prey, predators, and competitors. These peptides are produced by translating mRNA from many genes belonging to only a few gene superfamilies. Each translation product is processed to yield a great diversity of different mature toxin peptides (≈50,000–100,000), most of which are 12–30 aa in length with two to three disulfide crosslinks. In vitro, forming the biologically relevant disulfide configuration is often problematic, suggesting that in vivo mechanisms for efficiently folding the diversity of conotoxins have been evolved by the cone snails. We demonstrate here that the correct folding of a Conus peptide is facilitated by a posttranslationally modified amino acid, γ-carboxyglutamate. In addition, we show that multiple isoforms of protein disulfide isomerase are major soluble proteins in Conus venom duct extracts. The results provide evidence for the type of adaptations required before cone snails could systematically explore the specialized biochemical world of “microproteins” that other organisms have not been able to systematically access. Almost certainly, additional specialized adaptations for efficient microprotein folding are required.

Footnotes

↵ § To whom correspondence should be addressed. E-mail: olivera{at}biology.utah.edu.
This paper results from the Arthur M. Sackler Colloquium of the National Academy of Sciences, “Chemical Communication in a Post-Genomic World,” held January 17–19, 2003, at the Arnold and Mabel Beckman Center of the National Academies of Science and Engineering in Irvine, CA.
Abbreviations: PDI, protein disulfide isomerase; ER, endoplasmic reticulum.
↵ ¶ An obvious question is why γ-carboxyglutamate in C. textile peptide is not present in C. gloriamaris peptide. C. textile peptide is from a tropical Conus species from a warm, shallow-water habitat. C. gloriamaris peptide is from a deep-water species (≈100 fathoms); the significantly cooler habitat may minimize the pressure to facilitate folding by the presence of Gla. An alternative/additional rationale is that C. textile peptide is a major venom component, whereas C. gloriamaris peptide was never directly detected in venom, but only from a cDNA clone (implying that it may be a quantitatively minor venom component). A higher production rate would provide additional selective pressure for mechanisms that facilitate folding.