The cysteine‐cluster motif of c‐Src: Its role for the heavy metal‐mediated activation of kinase

We have previously reported that c-Src is activated by mercuric chloride (HgCl2). We investigated the mechanism of this activation and found that in vitro activation of c-Src by HgCl2 did not require tyrosine residues at 416 and 527. Both SH2 and SH3 domains of c-Src were dispensable for the activation by HgCl2. In contrast, iodoacetoamide (IAA) that binds to thiol side chain of cysteine blocked the activation of c-Src by HgCl2. To obtain more clues, each cysteine residue of c-Src was replaced with alanine. Of six cysteine residues in the kinase domain of c-Src, Cys483 and Cys498 located in the C-terminal portion as a cysteine-cluster (CC) motif were critical for the activation. In addition, other Src family kinases, Yes and Lyn, were activated by treatment with HgCl2, and cysteine residues, especially those correspond to Cys498 of Src in the CC motif of these kinases, were also required for the activation of the kinases by HgCl2. In addition to these observations, treatment of cells with HgCl2 dramatically activated the wild-type c-Src, whereas it could not activate the mutant form of Src with a substitution of Cys498. Taken together, our results disclose that cysteine residues in the CC motif of c-Src, Cys483 and Cys498, act as a module for the activation of the kinase by a heavy metal compound, mercuric chloride. (Cancer Sci 2008; 99: 571–575)