Cryo-EM structures of DNA-free and DNA-bound BsaXI: architecture of a Type IIB restriction-modification enzyme.

ABSTRACT: We have determined multiple cryogenic electron microscopy (cryo-EM) structures of the Type IIB restriction-modification enzyme BsaXI. Such enzymes cleave DNA on both sides of their recognition sequence and share features of Types I, II, and III restriction systems. BsaXI forms a heterotrimeric (RM)2S assemblage in the presence and absence of bound DNA. Two unique structural motifs-a multi-helical "knob" and a long antiparallel double-helical "paddle"-are involved in DNA binding and cleavage. Binding of the DNA target triggers a large conformational change from an 'open' to 'closed' configuration, resulting in a mixture of two different conformations with respect to the positioning of the S subunit and its target recognition domains on the enzyme's bipartite DNA target site. Structure-guide

SUBMITTER: Shen BW 

PROVIDER: S-EPMC11997821 | biostudies-literature | 2025 Apr

REPOSITORIES: biostudies-literature