7jw3

Publication Abstract from PubMed

Nibbler (Nbr) is a 3'-to-5' exoribonuclease whose catalytic 3'-end trimming activity impacts microRNA (miRNA) and PIWI-interacting RNA (piRNA) biogenesis. Here, we report on structural and functional studies to decipher the contributions of Nbr's N-terminal domain (NTD) and exonucleolytic domain (EXO) in miRNA 3'-end trimming. We have solved the crystal structures of the NTD core and EXO domains of Nbr, both in the apo-state. The NTD-core domain of Aedes aegypti Nbr adopts a HEAT-like repeat scaffold with basic patches constituting an RNA-binding surface exhibiting a preference for binding double-strand RNA (dsRNA) over single-strand RNA (ssRNA). Structure-guided functional assays in Drosophila S2 cells confirmed a principal role of the NTD in exonucleolytic miRNA trimming, which depends on basic surface patches. Gain-of-function experiments revealed a potential role of the NTD in recruiting Nbr to Argonaute-bound small RNA substrates. The EXO domain of A. aegypti and Drosophila melanogaster Nbr adopt a mixed alpha/beta-scaffold with a deep pocket lined by a DEDDy catalytic cleavage motif. We demonstrate that Nbr's EXO domain exhibits Mn(2+)-dependent ssRNA-specific 3'-to-5' exoribonuclease activity. Modeling of a 3' terminal Uridine into the catalytic pocket of Nbr EXO indicates that 2'-O-methylation of the 3'-U would result in a steric clash with a tryptophan side chain, suggesting that 2'-O-methylation protects small RNAs from Nbr-mediated trimming. Overall, our data establish that Nbr requires its NTD as a substrate recruitment platform to execute exonucleolytic miRNA maturation, catalyzed by the ribonuclease EXO domain.

Structure-function analysis of microRNA 3'-end trimming by Nibbler.,Xie W, Sowemimo I, Hayashi R, Wang J, Burkard TR, Brennecke J, Ameres SL, Patel DJ Proc Natl Acad Sci U S A. 2020 Dec 1;117(48):30370-30379. doi:, 10.1073/pnas.2018156117. Epub 2020 Nov 16. PMID:33199607^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.