Disulfide bridge reorganization induced by proline mutations in maurotoxin

Maurotoxin (MTX) is a 34-residue toxin that has been isolated from the veno m of the chactidae scorpion Scorpio maurus palmatus, and characterized. Tog ether with Pi1 and HsTx1, MTX belongs to a family of short-chain four-disul fide-bridged scorpion toxins acting on potassium channels. However, contrar y to other members of this family, MTX exhibits an uncommon disulfide bridg e organization of the type C1-C5, C2-C6, C3-C4 and C7-C8, versus C1-C5, C2- C6, C3-C7 and C4- C8 for both Pi1 and HsTx1. Here, we report that the subst itution of MTX proline residues located at positions 12 and/or 20, adjacent to C3 (Cys(13)) and C4 (Cys(19)), results in conventional Pi1- and HsTx1-l ike arrangement of the half-cystine pairings, In this case, this novel disu lfide bridge arrangement is without obvious incidence on the overall three- dimensional structure of the toxin. Pharmacological assays of this structur al analog, [A(12),A(20)]MTX, reveal that the blocking activities on Shaker B and rat Kv1.2 channels remain potent whereas the peptide becomes inactive on rat Kv1.3. These data indicate, for the first time, that discrete point mutations in MTX can result in a marked reorganization of the half-cystine pairings, accompanied with a novel pharmacological profile for the analog. (C) 2001 Federation of European Biochemical Societies. Published by Elsevi er Science B.V. All rights reserved.