Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 135, Issue 46, Pages 17476-17487Publisher
AMER CHEMICAL SOC
DOI: 10.1021/ja408729b
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Funding
- Government of Canada through Genome Canada
- Ontario Genomics Institute [2009-OGI-ABC-1405]
- Ontario Research Fund [ORF-GL2-01-004]
- Natural Science and Engineering Research Council of Canada
- U.S. National Institutes of Health [GM094585]
- U.S. Department of Energy, Office of Biological and Environmental Research [DE-AC02-06CH11357]
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Cas4 proteins, a core protein family associated with the microbial system of adaptive immunity CRISPR, are predicted to function in the adaptation step of the CRISPR mechanism. Here we show that the Cas4 protein SSO0001 from the archaeon Sulfolobus solfataricus has metal-dependent endonuclease and 5'-> 3' exonuclease activities against single-stranded DNA, as well as ATP-independent DNA unwinding activity toward double-stranded DNA. The crystal structure of SSO0001 revealed a decameric toroid formed by five dimers with each protomer containing one [4Fe-4S] cluster and one Mn2+ ion bound in the active site located inside the internal tunnel. The conserved RecB motif and four Cys residues are important for DNA binding and cleavage activities, whereas DNA unwinding depends on several residues located near the [4Fe-4S] cluster. Our results suggest that Cas4 proteins might contribute to the addition of novel CRISPR spacers through the formation of 3'-DNA overhangs and to the degradation of foreign DNA.
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