Pasteurellaceae ComE1 proteins combine the properties of fibronectin adhesins and DNA binding competence proteins

A novel fibronectin-binding protein from Pasteurella multocida (PM1665) that binds to the fibronectin type III(9-10) modules via two helix-hairpin-helix motifs has recently been described [1]. This protein shares homology with competence-related DNA-binding and uptake proteins (ComEA and ComE) from Gram-positive and Gram-negative bacteria. Here, we show that recombinant PM1665 (now designated ComE1) also binds to DNA through the same helix-hairpin-helix motifs required for fibronectin-binding. This binding to DNA is non sequence-specific and is confined to double-stranded DNA. We have cloned and expressed ComE1 proteins from five members of the Pasteurellaceae in order to further investigate the function(s) of these proteins. When expressed as recombinant GST-fusion proteins, all of the homologues bound both to fibronectin and to double-stranded DNA. Inactivation of the gene encoding the ComE1 homologue in Actinobacillus pleuropneumoniae indicates major roles for these proteins in at least two processes: natural transformation, and binding of bacteria to fibronectin.