Secrets of a quick basic editor
The basic editors of CRISPR-Cas9 consist of RNA-driven Cas proteins fused to an enzyme capable of deaminating a DNA nucleoside. No natural enzyme deaminates adenine DNA, so a breakthrough occurred when natural transfer RNA deaminase was fused to Cas9 and evolved to create an adenine base editor (ABE) acting on DNA. Subsequent evolution provided the enzyme ABE8e, which catalyzes deamination more than 1000-fold faster than early ABEs. Lapinaitė et al. we now present the structure of DNA-bound ABE8e 3.2 angstrom resolution in which the target adenine is replaced with an analog to retain the catalytic conformation. The structure, together with kinetic data comparing ABE8e with previous ABEs, explains how ABE8e edits DNA bases and could be information for a future database-editor project.
Science, this edition p. 566
CRISPR-Cas-led basic editors convert A • T to G • C or C • G to T • A in cellular DNA for more accurate genome modification. To understand the molecular basis of DNA adenosine deamination by adenine base editors (ABEs), we determined the structure of 3.2 angstrom-resolution cryoelectron microscopy ABE8e associated with a substrate in which the deaminase domain binds to DNA exposed to CRISPR-Cas9. R-loop complex. Kinetic and structural data suggest that ABE8e catalyzes DNA deamination up to 11100-fold faster than previous ABEs due to mutations that stabilize DNA substrates in a constrained, RNA-like conformation. In addition, accelerated ABE8e DNA deamination indicates that short-term DNA dissolution, which may occur during double-stranded DNA monitoring using CRISPR-Cas9, has not been observed in the past. These results explain ABE8e’s mediation of database editing results and inform the future design of base editors.