Effects of As(III) Binding on α-Helical Structure

Abstract

As(III) displays a wide range of effects in cellular chemistry. Surprisingly, the structural consequences of arsenic binding to peptides and proteins are poorly understood. This study utilizes model alpha-helical peptides containing two cysteine (Cys) residues in various sequential arrangements and spatial locations to study the structural effects of arsenic binding. With i, and i + 1, i + 2, or i + 3 arrangements, CD spectroscopy shows that As(III) coordination causes helical destabilization when Cys residues are located at central or C-terminal regions of the helix. Interestingly, arsenic binding to i, i + 3 positions results in the elimination of helical structure and the formation of a relatively stable alternate fold. In contrast, helical stabilization is observed for peptides containing i, i + 4 Cys residues, with corresponding pseudo pairwise interaction energies (Delta G(pw) degrees) of -1.0 and -0.7 kcal/mol for C-terminal and central placements, respectively. Binding affinities and association rate constants show that As(III) binding is comparatively insensitive to the location of the Cys residues within these moderately stable helices. These data demonstrate that As(III) binding can be a significant modulator of helical secondary structure.

Arsenite binding to synthetic peptides: The effect of increasing length between two cysteines

“…In the ten peptides studied by Donoghue et al [7] and Cline et al [8], 0-3 amino acids were present between the two C. In our studies, the peptides had as many as 5, 9, 14, and 17 intervening amino acids between the two cysteines. Therefore, our peptides have a larger intervening sequence between the two C than the other examples available in the published literature.…”

“…Therefore, our peptides have a larger intervening sequence between the two C than the other examples available in the published literature. When arsenite was bound to dithiol sites in peptides 6, 30, 16, 27, 26, and 28, there were 8,11,14,23,35, and 50 atoms in the bridged ring structure of the peptide, respectively.…”

An ArsR/SmtB Family Member Is Involved in the Regulation by Arsenic of the Arsenite Oxidase Operon in Thiomonas arsenitoxydans

“…As opposed to ArsR, binding of As(III) and As(V) to apo-AioF stabilizes it ( Fig. 1A; arrangement of two of the cysteine residues (Cys111 and Cys115, interval ϩ 4), which was shown to enhance the ␣-helical structure (40). Therefore, arsenic binding to AioF likely stabilizes the ␣5 helix forming the dimerization domain between the two subunits.…”

Heavy metals and their general toxicity for plants

“…The binding of As (III) to proteins can have profound effects on their folding. Among proteins that are known to bind As (III) are transcription factors, signal transduction proteins, metabolic enzymes, redox regulatory enzymes, and structural proteins (40,41).…”