Nickel Binding to the c-Src SH3 Domain Facilitates Crystallization.

INTRODUCTION: Numerous X-ray crystal structures of the c-Src SH3 domain have provided a large sampling of atomic-level information for this important signaling domain. Multiple crystal forms have been reported, with variable crystal lattice contacts and chemical crystallization conditions. MATERIALS AND METHODS: We crystallized the c-Src SH3 domain in a crystallization buffer containing NiCl2. RESULTS: A unique crystal structure of the Src SH3 domain in the trigonal space group H32 is determined to 1.45 Å resolution. Crystal packing and anomalous scattering reveal that this crystal form is mediated by two ordered nickel ions provided by the crystallization buffer. Nickel coordination occurs in a 2:2 stoichiometry, which dimerizes two SH3 domain monomers across a pseudo-twofold rotation axis and involves the native N-terminal c-Src SH3 amino acid sequence, a surface-exposed histidine residue, and ordered water molecules. DISCUSSION: This study provides an example of metal-mediated crystallization and metal binding by N-terminal protein residues, contrasting with the Amino-Terminal Copper and Nickel Binding (ATCUN) motif. CONCLUSION: Alternative avenues help widen the potential for future crystallography-based studies of the c-Src SH3 domain.