Abstract
Conjugation, besides transformation and transduction, is one of the main mechanisms of horizontal transmission of genetic information among bacteria. Conjugational transfer, due to its essential role in shaping bacterial genomes and spreading of antibiotics resistance genes, has been widely studied for more than 70 years. However, new and intriguing facts concerning the molecular basis of this process are still being revealed. Most recently, a novel family of conjugative relaxases (Mob proteins) was distinguished. The characteristic feature of these proteins is that they are not related to any of Mobs described so far. Instead of this, they share significant similarity to tyrosine recombinases. In this study MobK—a tyrosine recombinase-like Mob protein, encoded by pIGRK cryptic plasmid from the Klebsiella pneumoniae clinical strain, was characterized. This study revealed that MobK is a site-specific nuclease and its relaxase activity is dependent on both a conserved catalytic tyrosine residue (Y179) that is characteristic of tyrosine recombinases and the presence of Mg2+ divalent cations. The pIGRK minimal origin of transfer sequence (oriT) was also characterized. This is one of the first reports presenting tyrosine recombinase-like conjugative relaxase protein. It also demonstrates that MobK is a convenient model for studying this new protein family.
Highlights
Conjugational transfer (CT) is one of the main factors promoting DNA mobility and genetic diversity in a bacterial world [1,2]
The tyrosine recombinases (TRs)-like conjugative relaxase family consists of three representatives: MobK from pIGRK plasmid, MpsA encoded by SGI1 integrative and mobilizable elements (IMEs) element and TcpM from pCW3 plasmid
We showed that tyrosine residue Y179, conserved among TRs and acting as a nucleophile in TR DNA processing, is indispensable for MobK activity
Summary
Conjugational transfer (CT) is one of the main factors promoting DNA mobility and genetic diversity in a bacterial world [1,2]. A significant consequence of CT is the spreading of antibiotic resistance (AR) among pathogenic bacterial strains [4,5,6,7]. For these reasons, CT has been widely studied and extensive knowledge about the molecular bases of this process has been gained [3,8,9,10,11]. Innovatory strategies for preventing CT-dependent AR spread have been proposed [12] They rely on the use of specific inhibitors blocking each component of a CT system protein machinery [12,13,14,15,16,17]
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