The Molecular Basis of FimT-mediated DNA Uptake during Bacterial Natural Transformation

Abstract

Naturally competent bacteria encode sophisticated protein machinery for the uptake and translocation of exogenous DNA into the cell. If this DNA is integrated into the bacterial genome, the bacterium is said to be naturally transformed. Most competent bacterial species utilise type IV pili for the initial DNA uptake step. These proteinaceous cell-surface structures are composed of thousands of pilus subunits (pilins), designated as major or minor according to their relative abundance in the pilus. In this study, we show that the minor pilin FimT plays an important role in the natural transformation of Legionella pneumophila. We used NMR spectroscopy, in vitro DNA binding assays and in vivo transformation assays to understand the molecular basis of FimTs role in this process. FimT directly interacts with DNA via an electropositive patch, rich in arginines, several of which are well-conserved and located in FimTs conformationally flexible C-terminal tail. We also show that FimT orthologues from other Gammaproteobacteria share the ability to bind to DNA. Our functional characterisation and comprehensive bioinformatic analysis of FimT, suggest that it plays an important role for DNA uptake in a wide range of competent species.