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2011 ; 405
(4
): 939-55
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The structure of the CRISPR-associated protein Csa3 provides insight into the
regulation of the CRISPR/Cas system
#MMPMID21093452
Lintner NG
; Frankel KA
; Tsutakawa SE
; Alsbury DL
; Copié V
; Young MJ
; Tainer JA
; Lawrence CM
J Mol Biol
2011[Jan]; 405
(4
): 939-55
PMID21093452
show ga
Adaptive immune systems have recently been recognized in prokaryotic organisms
where, in response to viral infection, they incorporate short fragments of
invader-derived DNA into loci called clustered regularly interspaced short
palindromic repeats (CRISPRs). In subsequent infections, the CRISPR loci are
transcribed and processed into guide sequences for the neutralization of the
invading RNA or DNA. The CRISPR-associated protein machinery (Cas) lies at the
heart of this process, yet many of the molecular details of the CRISPR/Cas system
remain to be elucidated. Here, we report the first structure of Csa3, a
CRISPR-associated protein from Sulfolobus solfataricus (Sso1445), which reveals a
dimeric two-domain protein. The N-terminal domain is a unique variation on the
dinucleotide binding domain that orchestrates dimer formation. In addition, it
utilizes two conserved sequence motifs [Thr-h-Gly-Phe-(Asn/Asp)-Glu-X(4)-Arg and
Leu-X(2)-Gly-h-Arg] to construct a 2-fold symmetric pocket on the dimer axis.
This pocket is likely to represent a regulatory ligand-binding site. The
N-terminal domain is fused to a C-terminal MarR-like winged helix-turn-helix
domain that is expected to be involved in DNA recognition. Overall, the unique
domain architecture of Csa3 suggests a transcriptional regulator under allosteric
control of the N-terminal domain. Alternatively, Csa3 may function in a larger
complex, with the conserved cleft participating in protein-protein or
protein-nucleic acid interactions. A similar N-terminal domain is also identified
in Csx1, a second CRISPR-associated protein family of unknown function.