Nirwan N, Itoh Y, Singh P, Bandyopadhyay S, Vinothkumar KR, Amunts A, Saikrishnan K
Nat Commun 10 (1) 3058 [2019-07-11; online 2019-07-11]
The AAA+ GTPase McrB powers DNA cleavage by the endonuclease McrC. The GTPase itself is activated by McrC. The architecture of the GTPase and nuclease complex, and the mechanism of their activation remained unknown. Here, we report a 3.6 Å structure of a GTPase-active and DNA-binding deficient construct of McrBC. Two hexameric rings of McrB are bridged by McrC dimer. McrC interacts asymmetrically with McrB protomers and inserts a stalk into the pore of the ring, reminiscent of the γ subunit complexed to α 3β3 of F1-ATPase. Activation of the GTPase involves conformational changes of residues essential for hydrolysis. Three consecutive nucleotide-binding pockets are occupied by the GTP analogue 5'-guanylyl imidodiphosphate and the next three by GDP, which is suggestive of sequential GTP hydrolysis.
Cryo-EM maps and models are deposited in the Electron Microscopy and Protein Data Banks: EMD-0310 and 6HZ4. Maps and coordinates of five major classes are deposited — EMD-0311 and 6HZ5; EMD-0312 and 6HZ6; EMD-0313 and 6HZ7; EMD-0314 and 6HZ8; EMD-0315 and 6HZ9. Other data are available from the corresponding authors upon reasonable request.