The Clustered Regularly Interspaced Short _Palindromic Repeats （CRISPR）-CRISPR-associated （Cas） system is an adaptive immune system in bacteria and archaea that resists exogenous invasion through nucleic acid-medi...The Clustered Regularly Interspaced Short _Palindromic Repeats （CRISPR）-CRISPR-associated （Cas） system is an adaptive immune system in bacteria and archaea that resists exogenous invasion through nucleic acid-mediated cleavage. In the type III-A system, the Csm complex contains five effectors and a CRISPR RNA, which edits both single stranded RNA and double stranded DNA. It has recently been demonstrated that cyclic oligoadenylates （cOAs）, which are synthesized by the Csm complex, act as second messengers that bind and activate Csm6. Here, we report the crystal structures of Staphylococcus epiderrnidis Csm3 （SeCsm3） and an N-terminally truncated Csm6 （SeCsm6AN） at 2.26 and 2.0 A, respectively. The structure of SeCsm3 highly resembled previously reported Csm3 structures from other species; however, it provided novel observations allowing further enzyme characterization. The homodimeric SeCsm6AN folds into a compact structure. The dimerization of the HEPN domain leads to the formation of the ribonuclease active site, which is consistent with the reported Csm6 structures. Altogether, our studies provide a struc- tural view of the ribonuclease activity mediated by Csm3 and Csm6 of the type III-A CRISPR-Cas system.展开更多
基金supported by the National Natural Science Foundation of China(31570842 to W.C.)the National Young Thousand Talents Programthe Sichuan Province Thousand Talents Program in China
文摘The Clustered Regularly Interspaced Short _Palindromic Repeats （CRISPR）-CRISPR-associated （Cas） system is an adaptive immune system in bacteria and archaea that resists exogenous invasion through nucleic acid-mediated cleavage. In the type III-A system, the Csm complex contains five effectors and a CRISPR RNA, which edits both single stranded RNA and double stranded DNA. It has recently been demonstrated that cyclic oligoadenylates （cOAs）, which are synthesized by the Csm complex, act as second messengers that bind and activate Csm6. Here, we report the crystal structures of Staphylococcus epiderrnidis Csm3 （SeCsm3） and an N-terminally truncated Csm6 （SeCsm6AN） at 2.26 and 2.0 A, respectively. The structure of SeCsm3 highly resembled previously reported Csm3 structures from other species; however, it provided novel observations allowing further enzyme characterization. The homodimeric SeCsm6AN folds into a compact structure. The dimerization of the HEPN domain leads to the formation of the ribonuclease active site, which is consistent with the reported Csm6 structures. Altogether, our studies provide a struc- tural view of the ribonuclease activity mediated by Csm3 and Csm6 of the type III-A CRISPR-Cas system.
