IS21 family transposase cleaved donor complex traps two right-handed superhelical crossings

Transposases are ubiquitous enzymes that catalyze DNA rearrangement events with broad impacts on gene expression, genome evolution, and the spread of drug-resistance in bacteria. Here, we use biochemical and structural approaches to define the molecular determinants by which IstA, a transposase present in the widespread IS21 family of mobile elements, catalyzes efficient DNA transposition. Solution studies show that IstA engages the transposon terminal sequences to form a high-molecular weight complex and promote DNA integration. A 3.4 angstrom resolution structure of the transposase bound to transposon ends corroborates our biochemical findings and reveals that IstA self-assembles into a highly intertwined tetramer that synapses two supercoiled terminal inverted repeats. The three-dimensional organization of the IstA center dot DNA cleaved donor complex reveals remarkable similarities with retroviral integrases and classic transposase systems, such as Tn7 and bacteriophage Mu, and provides insights into IS21 transposition. Spinola-Amilibia et al. present the cryo-EM structure of the IS21 transposase in complex with the donor DNA and show that IstA recognizes the transposon ends with a highly intertwined configuration to facilitate the strand-transfer reaction.

Automated summary

Transposases are enzymes that play a role in DNA rearrangement and have broad impacts on gene expression, genome evolution, and the spread of drug-resistance in bacteria. This study investigates the molecular determinants of IstA, a transposase in the IS21 family, and reveals its structure and mechanism of action in DNA transposition. The research findings provide new insights into IS21 transposition.