Nickel binding to a split ATCUN motif in c-Src SH3 domain facilitates crystallization
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. Here, we report a unique crystal structure of Src SH3 domain in trigonal space group H32 to 1.45 [A] 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. This study provides an example of metal binding by N-terminal protein residues that contrasts the amino terminal copper and nickel binding (ATCUN) motif and is an alternative avenue for crystallization of the Src SH3 domain. STRUCTURED ABSTRACTO_ST_ABSIntroductionC_ST_ABSNumerous 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 MethodsWe crystallize the c-Src SH3 domain in a crystallization buffer containing NiCl2. ResultsA unique crystal structure of Src SH3 domain in trigonal space group H32 to 1.45 [A] resolution is determined. 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. DiscussionThis study provides an example of metal-mediated crystallization and metal binding by N-terminal protein residues that contrasts the amino terminal copper and nickel binding (ATCUN) motif. ConclusionAlternative avenues for helps widen the potential for future crystallography-based studies of the c-Src SH3 domain.