RESUMO
The carboxyl terminus of the S3 segment (S3C) in voltage-gated potassium channels was suggested to be the binding site of gating modifier toxins like hanatoxin. It has also been proposed to have a helical secondary structural arrangement. The currently available structures in high resolution for such channel molecules are restricted to regions illustrating the pore function. Therefore no further direct experimental data to elucidate the detailed mechanism for such toxin binding can be derived. In order to examine the putative three-dimensional structure of S3C and to analyze the residues required for hanatoxin binding, molecular simulation and docking were performed, based on the solution structure of hanatoxin and the structural information from mutational scanning data for the S3C fragment in Kv2.1. Our results indicate that hydrophobic and electrostatic interactions are both utilized to stabilize the toxin binding. Precise docking residues and the appropriate orientation for binding regarding amphipathic environments are also described. Compared with the functional data proposed by previous studies, the helical structural arrangement for the C-terminus of the S3 segment in voltage-gated potassium channels can therefore be further emphasized and analyzed. The possible location/orientation for toxin binding with respect to membrane distribution around the S3C segment is also discussed in this paper.
