DSSR-PyMOL cartoon-block schematics: PDB entry 7mcs

PDB-id

7mcs; SNAP-derived features in text and JSON formats

Class

DNA binding protein-DNA

Method

cryo-EM (3.56 Å)

Summary

Cryo-electron microscopy structure of tnsc(1-503)a225v bound to DNA

Reference

Shen Y, Gomez-Blanco J, Petassi MT, Peters JE, Ortega J, Guarne A (2022): "Structural basis for DNA targeting by the Tn7 transposon." Nat.Struct.Mol.Biol., 29, 143-151. doi: 10.1038/s41594-022-00724-8.

Abstract

Tn7 transposable elements are unique for their highly specific, and sometimes programmable, target-site selection mechanisms and precise insertions. All the elements in the Tn7 family utilize an AAA+ adaptor (TnsC) to coordinate target-site selection with transpososome assembly and to prevent insertions at sites already containing a Tn7 element. Owing to its multiple functions, TnsC is considered the linchpin in the Tn7 element. Here we present the high-resolution cryo-EM structure of TnsC bound to DNA using a gain-of-function variant of the protein and a DNA substrate that together recapitulate the recruitment to a specific DNA target site. TnsC forms an asymmetric ring on target DNA that segregates target-site selection and interaction with the paired-end complex to opposite faces of the ring. Unlike most AAA+ ATPases, TnsC uses a DNA distortion to find the target site but does not remodel DNA to activate transposition. By recognizing pre-distorted substrates, TnsC creates a built-in regulatory mechanism where ATP hydrolysis abolishes ring formation proximal to an existing element. This work unveils how Tn7 and Tn7-like elements determine the strict spacing between the target and integration sites.