Arsenic(III)-cysteine interactions stabilize three-helix bundles in aqueous solution

Tri L12C and Tri L16C are amphiphilic peptides composed of 30 amino acids with cysteine in either the 12 or 16 position of the sequence. In the absence of metal, the peptides form two- (pH < 5.5) and three-helix bundles (pH > 7). The preference of As(III) for trigonal-pyramidal geometry and thiol coordination is used to direct folding of the peptide to form three-helix bundles under all conditions studied. These observations are contrasted with previous Hg(II) complexation in which both linear Hg(II) bis thiolate (two-helix bundle) and trigonal tris thiolate (three-helix bundle) binding motifs were observed.