Solution structure of BmKTX, a K+ blocker toxin from the Chinese scorpionButhus Martensi

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Abstract
BmKTX is a toxin recently purified from the venom of Buthus Martensi, which belongs to the kaliotoxin family. We have determined its solution structure by use of conventional two‐dimensional NMR techniques followed by distance‐geometry and energy minimization. The calculated structure is composed of a short α‐helix (residues 14 to 20) connected by a tight turn to a two‐stranded antiparallel β‐sheet (sequences 25–27 and 32–34). The β‐turn connecting these strands belongs to type I. The N‐terminal segment (sequence 1 to 8) runs parallel to the β‐sheet although it cannot be considered as a third strand. Comparison of the conformation of BmKTX and toxins of the kaliotoxin familyclearly demonstrates that they are highly related. Therefore, analysis of the residues belonging to the interacting surface of those toxins allows us to propose a functional map of BmKTX slightly different from the one of KTX and AgTX2, which may explain the variations in affinities of these toxins towardsthe Kv1.3 channels. Proteins 2000;38:70–78.