Characterization of the putative lipase motif of Agrobacterium virulence protein VirJ

Abstract

A function important for Agrobacterium tumefaciens gene transfer is redundantly encoded on theTi plasmid and the chromosome. A gene named virJ located on the Ti plasmid of some strains can functionally complement a chromosomal gene (acvB) mutant. Both AcvB and VirJ contain a putative lipase or acyltransferase motif. Mutation of the lipase motif would lead to the malfunctioning of the proteins. To understand the biochemical function of VirJ, genetic and biochemical experiments were carried out to further characterize VirJ. Experimental data have shown that mutation of virJ has no effect on the LPS or lipid profile of A. tumefaciens, based on thin-layer chromatography, SDS-PAGE analysis and electrospray ionization (ESI) ion-trap mass spectrometry (MS) analysis. Protein-protein interaction study has indicated that VirJ could interact with VirD2, VirE2, VirD4 and AopB but not with VirB7, VirB8, VirB10 and VirB11. Polypeptides of VirB7 purified from the wild-type and virJ-acvB double mutants did not exhibit any difference, suggesting that VirJ plays a role in a function other than the posttranslational modification of VirB7.