Comparisons of the D-galactose- and D-ribose-binding protein amino acid sequences and secondary structure predictions with the known primary and three-dimensional structure of L-arabinose-binding protein suggest that the three proteins have similar molecular structures. These studies also indicate an evolutionary relationship among the proteins. One region of striking homology between the galactose- and ribose-binding proteins suggests that this may be th protein-protein contact site for interaction with the membrane-bound chemotaxis receptor. The ligands and the geometry of the galactose binding site are also predicted.
