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Structural highlights

Function

CS13A_LEPBD 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 (spacer sequences) and target invading nucleic acids. Unlike many single-component effectors, this CRISPR-Cas system targets RNA (PubMed:27669025). CRISPR clusters are transcribed from pre-CRISPR RNA (crRNA) and processed into crRNA by this protein (PubMed:27669025, PubMed:28475872, PubMed:28757251). pre-crRNA processing yields a 5'-OH and probably a 2',3'-cyclic phosphate (PubMed:27669025). Also cleaves pre-crRNA from several other type VI-A CRISPR systems (PubMed:28475872). Cleaves linear target ssRNA in a crRNA-dependent fashion, preferentially before U residues (PubMed:27669025, PubMed:28475872). Cleavage of target ssRNA is about 80-fold faster than pre-crRNA processing and uses a different active site (PubMed:27669025). Binding a viable target RNA target activates this protein for non-specific RNA degradation in vitro (called collateral RNA degradation) (PubMed:27669025, PubMed:28475872, PubMed:28757251). Activation occurs with 10 fM target RNA (PubMed:28475872). crRNA maturation is not essential for activation of RNA degradation, but lack of mature crRNA (due to mutagenesis) decreases activation levels (PubMed:28475872). This system has a 3' protospacer flanking site in the target RNA (PFS), which is C and unavailable to base pair with crRNA (PFS is equivalent to PAM, the protospacer adjacent motif) (PubMed:28757251).^{[1] [2] [3]}

References

1. ↑ East-Seletsky A, O'Connell MR, Knight SC, Burstein D, Cate JH, Tjian R, Doudna JA. Two distinct RNase activities of CRISPR-C2c2 enable guide-RNA processing and RNA detection. Nature. 2016 Oct 13;538(7624):270-273. doi: 10.1038/nature19802. Epub 2016 Sep, 26. PMID:27669025 doi:http://dx.doi.org/10.1038/nature19802
2. ↑ East-Seletsky A, O'Connell MR, Burstein D, Knott GJ, Doudna JA. RNA Targeting by Functionally Orthogonal Type VI-A CRISPR-Cas Enzymes. Mol Cell. 2017 May 4;66(3):373-383.e3. PMID:28475872 doi:10.1016/j.molcel.2017.04.008
3. ↑ Liu L, Li X, Ma J, Li Z, You L, Wang J, Wang M, Zhang X, Wang Y. The Molecular Architecture for RNA-Guided RNA Cleavage by Cas13a. Cell. 2017 Aug 10;170(4):714-726.e10. doi: 10.1016/j.cell.2017.06.050. Epub 2017 , Jul 27. PMID:28757251 doi:http://dx.doi.org/10.1016/j.cell.2017.06.050
4. ↑ Liu L, Li X, Ma J, Li Z, You L, Wang J, Wang M, Zhang X, Wang Y. The Molecular Architecture for RNA-Guided RNA Cleavage by Cas13a. Cell. 2017 Aug 10;170(4):714-726.e10. doi: 10.1016/j.cell.2017.06.050. Epub 2017 , Jul 27. PMID:28757251 doi:http://dx.doi.org/10.1016/j.cell.2017.06.050