Advances in the study of the structure of cas13a (also known as C2c2), a VI-type CRISPR-Cas system-effect protein.

On July 27th Cell, a leading international journal, published online new advances made by Wang Yanli and Zhang Xinzheng of the Institute of Biophysics of the Chinese Academy of Sciences in the structural study of the VI-TYPE CRISPR-Cas system-effect protein Cas13a (also known as C2c2).
the study successfully analyzed the crystal structure of Cas13a and crRNA (CRISPR-RNA) and its target RNA triple complex 3.08?, cas13a and crRNA binary 3.2?2 in Leptotrichia buccalis (Lbu) bacteria.
results confirm that the binding of target RNA leads to image changes in two HEPN domains of LbuCas13a that perform RNA interference functions, thus stimulating the enzyme-cutting activity of LbuCas13a non-specific cutting of any single-stranded RNA.
the results provide an important structural biology basis for the study of the molecular mechanisms by which Cas13a performs RNA enzyme activity.
the study is another major breakthrough after Wang's team first reported in Cell in January that Cas13a and crRNA binary complexes in Leptotrichia Shahii (Lsh) bacteria and crystal structures in Cas13a's free state.
almost all ancient bacteria and about 50% of bacteria have CRISPR-Cas systems to fight viruses and particles.
CRISPR-Cas system is divided into two categories, Cas13a is the second largest type of VI system of the effect protein, with RNA-mediated RNA enzyme cutting activity, is currently the second largest type of CRISPR-Cas system found that the only protein that can degrade RNA (Cas9, Cpf1, C2c1 are RNA-mediated DNA nucleic acid cut enzymes), for the development of research tools to expand the use of SPR system gene editing has significant value.
study, the researchers used X-ray crystallography to successfully analyze the 3-way composite structure of LbuCas13a-crRNA-target RNA (3.08?).
, the binary complex structure of 3.2 sLbuCas13a-crRNA was obtained by freezing electron mirror technology.
structure shows that Cas13a has two reC and NUC blades, wherein the NUC blade contains two HEPN domains, the Helical-2 domain, and the connecting domain connecting the two HEPN domains, two HEPN domains make up the active region of Cas13a cutting target RNA.
the complementary target RNA of the crRNA identification sequence and bind to it to form a double-stranded RNA surrounded by THEC blades.
the same time, the formation of double-stranded RNA causes changes in the composition of crRNA and Cas13a proteins, pushing the two HEPN domains closer to each other to activate the Cas13a protein.
researchers have demonstrated through structural and functional studies that Cas13a, activated by crRNA and target RNA, can cut any single-stranded RNA.
The study provides a reliable structural basis for the further development of CRISPR-Cas13a system, provides strong evidence for a deep understanding of the molecular mechanisms of bacteria against virus invasion, and is of great significance for the prevention, detection, control and treatment of virus-induced diseases, especially based on Cas13a's efficient RNA enzyme cutting activity, which has great prospects for rapid detection of various major diseases.
Yanli and Zhang Xinzheng are co-authors of this article.
Liu Liang, a postdoctoral student in Wang Yanli Group, Li Xueyan, a graduate student, Li Zongqiang, a staff member, and Ma Jun, an associate researcher in Zhang's New Deal Group, are the co-authors of this paper.
The research was funded by the Ministry of Science and Technology, the National Natural Science Foundation of China, the Chinese Academy of Sciences Strategic Pilot Science and Technology (Category B) and the National Youth Thousand People Project, and provided important technical support for the research by the Shanghai Synchrogenic Radiation Light Source (SSRF), the Japanese Synchrogenic Radiation Light Source Spring-8, and the Bioimaging Center of the Institute of Biophysics.
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