Phylogenetic survey of soluble saxitoxin-binding activity in pursuit of the function and molecular evolution of saxiphilin, a relative of transferrin

Abstract

Saxiphilin is a soluble protein of unknown function which binds the neurotoxin, saxitoxin (STX), with high affinity. Molecular characterization of saxiphilin from the North American bullfrog, Rana catesbeiana, has previously shown that it is a member of the transferrin family. In this study we surveyed various animal species to investigate the phylogenetic distribution of saxiphilin, as detected by the presence of soluble [$H]STX binding activity in plasma, haemolymph or tissue extracts. We found that saxiphilin activity is readily detectable in a wide variety of arthropods, fish, amphibians, and reptiles. The pharmacological characteristics of [$H]STX binding activity in phylogenetically diverse species indicates that a protein homologous to bullfrog saxiphilin is likely to be constitutively expressed in many ectothermic animals. The results suggest that the saxiphilin gene is evolutionarily as old as an ancestral gene encoding bilobed transferrin, an Fe$ + -binding and transport protein which has been identified in several arthropods and all the vertebrates which have been studied.

Geographical Segregation of the Neurotoxin-Producing Cyanobacterium Anabaena circinalis

“…This, however, seems unlikely since all A. circinalis strains analyzed were cultured under the same conditions. In addition, there are limitations on the techniques currently used to measure toxicity (19,20,23,24), and growth phase regulation of toxin production has been demonstrated (25). A. circinalis grown in culture may also undergo mutations which could affect toxin production, as has been found with Microcystis aeruginosa (Tillett and Neilan, unpublished).…”

Cyanobacterial toxins – occurrence, biosynthesis and impact on human affairs

“…Clams and crabs can bioaccumulate PSP toxins in high concentrations, and appear to be insensitive to them, but posing risk to their predators and humans [121,122]. Receptors for PSP toxins discovered in the circulatory fluids of aquatic animals such as amphibian, fish, reptiles, and arthropods, seem to provide protection from the toxin [123].…”

Saxiphilin, a Saxitoxin-binding Protein with Two Thyroglobulin Type 1 Domains, Is an Inhibitor of Papain-like Cysteine Proteinases

“…In particular, the demonstration of a tight complex formation with papain opens the possibility of using inactivated papain affinity chromatography for purification and isolation of saxiphilin and other variants of this protein expressed by diverse animal species (18).…”