Structure-function studies reveal ComEA contains an oligomerization domain essential for transformation in...

An essential step in bacterial transformation is the uptake of DNA into the periplasm, across the thick peptidoglycan cell wall of Gram-positive bacteria, or the outer membrane and thin peptidoglycan layer of Gram-negative bacteria. ComEA, a DNA-binding protein widely conserved in transformable bacteria, is required for this uptake step. Here we determine X-ray crystal structures of ComEA from two Gram-positive species, Bacillus subtilis and Geobacillus stearothermophilus, identifying a domain that is absent in Gram-negative bacteria. X-ray crystallographic, genetic, and analytical ultracentrifugation (AUC) analyses reveal that this domain drives ComEA oligomerization, which we show is required for transformation. We use multi-wavelength AUC (MW-AUC) to characterize the interaction between DNA and the ComEA DNA-binding domain. Finally, we present a model for the interaction of the ComEA DNA-binding domain with DNA, suggesting that ComEA oligomerization may provide a pulling force that drives DNA uptake across the thick cell walls of Gram-positive bacteria.