BACTERIAL BINDING PROTEIN-DEPENDENT PERMEASES - CHARACTERIZATION OF DISTINCTIVE SIGNATURES FOR FUNCTIONALLY RELATED INTEGRAL CYTOPLASMIC MEMBRANE-PROTEINS

Bacterial binding protein-dependent transport systems belong to the su perfamily of ABC transporters, which is widely distributed among livin g organisms. Their hydrophobic membrane proteins are the least charact erized components. The primary structures of 61 integral membrane prot eins from 35 uptake systems were compared in order to characterize a s hort conserved hydrophilic segment, with a consensus EAA - - - G - - - - - - - - -I - LP, located approximately 100 residues from the C-term inus. Secondary structure predictions indicated that this conserved re gion might be formed by two amphipathic alpha-helices connected by a l oop containing the invariant G residue. We classified the conserved mo tifs and found that membrane proteins from systems transporting struct urally related substrates specifically display a greater number of ide ntical residues in the conserved region. We determined a consensus for each class of membrane protein and showed that these can be considere d as signatures.