Lapemis toxin

Figure 3. Examples of neurotoxins (A, C) and a cardiotoxin (B). (A) Primary structure of lapemis toxin, a short-chain postsynaptic neurotoxin. (B) Cardiotoxin from Naja naja venom. (C) Toxin B from Naja naja venom.

Figure 4. Chemical structure of lapemis toxin showing three main loops A, B, and C.

The acetylcholine receptor and a neurotoxin form a noncovalent bond-type complex. The most important question is what portion of a neurotoxin is really involved in the receptor binding. Is it a particular residue, or are several residues involved Figure 4 is a two-dimensional structure of a postsynaptic neurotoxin— lapemis toxin from Lapemis hardwickii— that is based on the x-ray diffraction study of another similar toxin. 

Lapemis toxin Peptide Al Peptide B2 Peptide B1 Peptide Cl... 

Hydrophilicity analysis of lapemis toxin showed that the central loop is the most hydrophilic region. Since the ligand-binding region of the acetylcholine receptor is in the outside of the cell membranes, it is also hydrophilic. Therefore, it is also logical that the most hydrophilic portion of neurotoxin binds to the acetylcholine receptor-ligand-binding site, which is also hydrophilic. 

Miller, R. A., and Tu, A. T. (1991). Structure-function relationship of lapemis toxin A synthetic approach. Arch. Biochem. Biophys. 291 69-75. 

Tu, A. T., and Hong, B. S. (1971). Purification and chemical studies of a toxin from the venom of Lapemis hardwickii (Hardwick s sea snake). J. Biol. Chem. 246 2772-2779. 

---