Membrane binding motif of the P-type cardiotoxin

Carditoxins (CTXs) from cobra snake venoms, the basic 60-62 residue all-bet a sheet polypeptides, are known to bind to and impair the function of cell membranes. To assess the membrane induced conformation and orientation of C TXs, the interaction of the P-type cardiotoxin II from Naja oxiana snake ve nom (CTII) with perdeuterated dodecylphosphocholine (DPC) was studied using H-1-NMR spectroscopy and diffusion measurements. Under conditions where th e toxin formed a well-defined complex with DPC, the spatial structure of CT II with respect to the presence of tightly bound water molecules in loop II , was calculated using the torsion angle dynamics program DYANA. The struct ure was found to be similar, except for subtle changes in the tips of all t hree loops, to the previously described "major" form of CTII in aqueous sol ution illustrated by the "trans" configuration of the Val7-Pro8 peptide bon d. No "minor" form with the "cis" configuration of the above bond was found in the micelle-bound state. The broadening of the CTII backbone proton sig nals by 5, 16-doxylstearate relaxation probes, together with modeling based on the spatial structure of CTII, indicated a periphery mode of binding of the toxin molecule to the micelle and revealed its micelle interacting dom ain. The latter includes a hydrophobic region of CTII within the extremitie s of loops I and III (residues 5-11, 46-50), the basement of loop II (resid ues 24-29,31-37) and the belt of polar residues encircling these loops (lys ines 4,5,12,23,50, serines 11,46, histidine 31, arginine 36). It is suggest ed that this structural motif and the mode of binding can be realized durin g interaction of CTXs with lipid and biological membranes. (C) 2001 Academi c Press.