A FAMILY OF HOMOLOGOUS SUBSTRATE-BINDING PROTEINS WITH A BROAD RANGE OF SUBSTRATE-SPECIFICITY AND DISSIMILAR BIOLOGICAL FUNCTIONS

The uptake of peptides is accomplished mainly by a family of homologou s oligopeptide or dipeptide transporters in bacteria. Computer-aided s equence analyses expand members of the oligopeptide-binding protein fa mily to nickel and heme permeases and other proteins, including an enz yme hyaluronate synthase. They are involved in human pathogenicity, ba cterial virulence, substrate-sensing, bacterial conjugation and bacter ial metabolic reactions distinct from nutrient uptake. These homologou s proteins are found in both purple bacteria and Gram-positive bacteri a, indicating the presence of a common ancestor before the appearance of the two eubacterial phyla. Nevertheless, the pheromone-binding prot eins, involved in bacterial conjugation, and the hyaluronate synthase are present only in the low G-C Cram-positive eubacteria subdivision, which suggests that these proteins diverged from the common ancestor a fter the appearance of this subdivision.