Definition of a saxitoxin (STX) binding code enables discovery and characterization of the anuran saxiphilin family

Zhou Chen; Sandra Zakrzewska; Holly S Hajare; Aurora Alvarez-Buylla; Fayal Abderemane-Ali; Maximiliana Bogan; Dave Ramirez; Lauren A O'Connell; J Du Bois; Daniel L Minor Jr

doi:10.1073/pnas.2210114119

Definition of a saxitoxin (STX) binding code enables discovery and characterization of the anuran saxiphilin family

Proc Natl Acad Sci U S A. 2022 Nov;119(44):e2210114119. doi: 10.1073/pnas.2210114119. Epub 2022 Oct 24.

Authors

Affiliations

¹ Cardiovascular Research Institute, University of California, San Francisco, CA 94158.
² Department of Chemistry, Stanford University, Stanford, CA 94305.
³ Department of Biology, Stanford University, Stanford, CA 94305.
⁴ Department of Biochemistry and Biophysics, University of California, San Francisco, CA 94158.
⁵ Department of Cellular and Molecular Pharmacology, University of California, San Francisco, CA 94158.
⁶ California Institute for Quantitative Biomedical Research, University of California, San Francisco, CA 94158.
⁷ Kavli Institute for Fundamental Neuroscience, University of California, San Francisco, CA 94158.
⁸ Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720.

Abstract

American bullfrog (Rana castesbeiana) saxiphilin (RcSxph) is a high-affinity "toxin sponge" protein thought to prevent intoxication by saxitoxin (STX), a lethal bis-guanidinium neurotoxin that causes paralytic shellfish poisoning (PSP) by blocking voltage-gated sodium channels (Na_Vs). How specific RcSxph interactions contribute to STX binding has not been defined and whether other organisms have similar proteins is unclear. Here, we use mutagenesis, ligand binding, and structural studies to define the energetic basis of Sxph:STX recognition. The resultant STX "recognition code" enabled engineering of RcSxph to improve its ability to rescue Na_Vs from STX and facilitated discovery of 10 new frog and toad Sxphs. Definition of the STX binding code and Sxph family expansion among diverse anurans separated by ∼140 My of evolution provides a molecular basis for understanding the roles of toxin sponge proteins in toxin resistance and for developing novel proteins to sense or neutralize STX and related PSP toxins.

Keywords: anuran; saxiphilin; saxitoxin; toxin resistance.

Publication types

Research Support, Non-U.S. Gov't
Research Support, N.I.H., Extramural
Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

Animals
Carrier Proteins / metabolism
Guanidine
Ligands
Neurotoxins*
Rana catesbeiana
Saxitoxin* / genetics

Substances

Saxitoxin
Ligands
Neurotoxins
Guanidine
Carrier Proteins

Abstract

Publication types

MeSH terms

Substances

Grants and funding