Structural highlights
Function
[CAS6_PSEAB] CRISPR (clustered regularly interspaced short palindromic repeat) is an adaptive immune system that provides protection against mobile genetic elements (viruses, transposable elements and conjugative plasmids). CRISPR clusters contain sequences complementary to antecedent mobile elements and target invading nucleic acids. CRISPR clusters are transcribed and processed into CRISPR RNA (crRNA). Processes pre-crRNA into individual crRNA units. Absolutely required for crRNA production or stability. Upon expression in E.coli endonucleolytically processes pre-crRNA, although disruption and reconstitution experiments indicate that in situ other genes are also required for processing. Yields 5'-hydroxy and 3'-phosphate groups. The Csy ribonucleoprotein complex binds target ssDNA with high affinity but target dsDNA with much lower affinity.[1] [2] [3]
Publication Abstract from PubMed
CRISPR-Cas adaptive immune systems protect prokaryotes against foreign genetic elements. crRNAs derived from CRISPR loci base pair with complementary nucleic acids, leading to their destruction. In Pseudomonas aeruginosa, crRNA biogenesis requires the endoribonuclease Csy4, which binds and cleaves the repetitive sequence of the CRISPR transcript. Biochemical assays and three co-crystal structures of wild-type and mutant Csy4/RNA complexes reveal a substrate positioning and cleavage mechanism in which a histidine deprotonates the ribosyl 2'-hydroxyl pinned in place by a serine, leading to nucleophilic attack on the scissile phosphate. The active site catalytic dyad lacks a general acid to protonate the leaving group and positively charged residues to stabilize the transition state, explaining why the observed catalytic rate constant is approximately 10(4)-fold slower than that of RNase A. We show that this RNA cleavage step is essential for assembly of the Csy protein-crRNA complex that facilitates target recognition. Considering that Csy4 recognizes a single cellular substrate and sequesters the cleavage product, evolutionary pressure has likely selected for substrate specificity and high-affinity crRNA interactions at the expense of rapid cleavage kinetics.
Csy4 relies on an unusual catalytic dyad to position and cleave CRISPR RNA.,Haurwitz RE, Sternberg SH, Doudna JA EMBO J. 2012 Apr 20. doi: 10.1038/emboj.2012.107. PMID:22522703[4]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
See Also
References
- ↑ Haurwitz RE, Jinek M, Wiedenheft B, Zhou K, Doudna JA. Sequence- and structure-specific RNA processing by a CRISPR endonuclease. Science. 2010 Sep 10;329(5997):1355-8. PMID:20829488 doi:10.1126/science.1192272
- ↑ Cady KC, O'Toole GA. Non-identity-mediated CRISPR-bacteriophage interaction mediated via the Csy and Cas3 proteins. J Bacteriol. 2011 Jul;193(14):3433-45. doi: 10.1128/JB.01411-10. Epub 2011 Mar, 11. PMID:21398535 doi:http://dx.doi.org/10.1128/JB.01411-10
- ↑ Haurwitz RE, Sternberg SH, Doudna JA. Csy4 relies on an unusual catalytic dyad to position and cleave CRISPR RNA. EMBO J. 2012 Apr 20. doi: 10.1038/emboj.2012.107. PMID:22522703 doi:10.1038/emboj.2012.107
- ↑ Haurwitz RE, Sternberg SH, Doudna JA. Csy4 relies on an unusual catalytic dyad to position and cleave CRISPR RNA. EMBO J. 2012 Apr 20. doi: 10.1038/emboj.2012.107. PMID:22522703 doi:10.1038/emboj.2012.107
