Structure of a CRISPR-associated protein Cas2 from Desulfovibrio vulgaris

CRISPRs (clustered regularly interspaced short palindromic repeats) provide bacteria and archaea with RNA-guided acquired immunity to invasive DNAs. CRISPR-associated (Cas) proteins carry out the immune effector functions. Cas2 is a universal component of the CRISPR system. Here, a 1.35 Å resolution crystal structure of Cas2 from the bacterium Desulfovibrio vulgaris (DvuCas2) is reported. DvuCas2 is a homodimer, with each protomer consisting of an N-­terminal [beta][alpha][beta][beta][alpha][beta] ferredoxin fold (amino acids 1-78) to which is appended a C-terminal segment (amino acids 79-102) that includes a short 3₁₀-helix and a fifth [beta]-strand. The [beta]5 strands align with the [beta]4 strands of the opposite protomers, resulting in two five-stranded antiparallel [beta]-sheets that form a sandwich at the dimer interface. The DvuCas2 dimer is stabilized by a distinctive network of hydrophilic cross-protomer side-chain interactions.