A novel conserved protein region - the BON (bacterial OsmY and nodulation) domain - is found in the bacterial osmotic-shock-resistance protein OsmY, a family of haemolysins, a group of nodulation specificity proteins and secretory channels, and several hypothetical proteins. Functional annotation in the literature suggests that it interacts with phospholipid membranes. A lack of catalytic residues in the sequence alignment supports the hypothesis that it is a binding domain.