Abstract
SummaryRelaxases play essential roles in conjugation, the main process by which bacteria exchange genetic material, notably antibiotic resistance genes. They are bifunctional enzymes containing a trans-esterase activity, which is responsible for nicking the DNA strand to be transferred and for covalent attachment to the resulting 5′-phosphate end, and a helicase activity, which is responsible for unwinding the DNA while it is being transported to a recipient cell. Here we show that these two activities are carried out by two conformers that can both load simultaneously on the origin of transfer DNA. We solve the structure of one of these conformers by cryo electron microscopy to near-atomic resolution, elucidating the molecular basis of helicase function by relaxases and revealing insights into the mechanistic events taking place in the cell prior to substrate transport during conjugation.
Highlights
Horizontal gene transfer (HGT) is the main process by which bacteria exchange genetic material and plays crucial roles in bacterial adaptation and evolution
Open and Closed States of TraI Purified TraI (Figure 1B, left) on its own is prone to aggregation and does not crystallize, nor does it produce particles analyzable by cryo-EM (Figure S1). This led us to examine the behavior of TraI in a complex with a number of singlestranded DNA (ssDNA) derived from the sequence of oriT, its natural substrate
Depending on the oligonucleotide bound, TraI exhibits two conformations: one, observed when the ssDNA is bound to the trans-esterase domain, is open and accessible to proteolytic cleavage, while the other, observed when ssDNA is bound to the helicase domains, is closed and less accessible to protease degradation
Summary
Horizontal gene transfer (HGT) is the main process by which bacteria exchange genetic material and plays crucial roles in bacterial adaptation and evolution. Conjugative T4S systems in Gram-negative bacteria are composed of 12 components, termed VirB1–11 and VirD4, that form a large, multi-megadalton complex spanning the double membrane (Ilangovan et al, 2015). This large complex recruits its substrate, singlestranded DNA (ssDNA), and translocates it into a recipient cell via an extracellular pilus (Costa et al, 2016). End-joining occurs once transport of the nucleo-protein complex is complete
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
