PROSITE documentation PDOC00798

Bacterial extracellular solute-binding proteins, family 3 signature

Bacterial high affinity transport systems are involved in active transport of solutes across the cytoplasmic membrane. The protein components of these traffic systems include one or two transmembrane protein components, one or two membrane-associated ATP-binding proteins (ABC transporters; see <PDOC00185>) and a high affinity periplasmic solute-binding protein. The later are thought to bind the substrate in the vicinity of the inner membrane, and to transfer it to a complex of inner membrane proteins for concentration into the cytoplasm.

In gram-positive bacteria which are surrounded by a single membrane and have therefore no periplasmic region the equivalent proteins are bound to the membrane via an N-terminal lipid anchor. These homolog proteins do not play an integral role in the transport process per se, but probably serve as receptors to trigger or initiate translocation of the solute throught the membrane by binding to external sites of the integral membrane proteins of the efflux system.

In addition at least some solute-binding proteins function in the initiation of sensory transduction pathways.

On the basis of sequence similarities, the vast majority of these solute-binding proteins can be grouped [1] into eight families of clusters, which generally correlate with the nature of the solute bound.

Family 3 groups together specific amino acids and opine-binding periplasmic proteins and a periplasmic homolog with catalytic activity:

• Histidine-binding protein (gene hisJ) of Escherichia coli and related bacteria. An homologous lipoprotein exists in Neisseria gonorrhoeae.
• Lysine/arginine/ornithine-binding proteins (LAO) (gene argT) of Escherichia coli and related bacteria are involved in the same transport system than hisJ. Both solute-binding proteins interact with a common membrane-bound receptor hisP of the binding protein dependent transport system HisQMP.
• Glutamine-binding proteins (gene glnH) of Escherichia coli and Bacillus stearothermophilus.
• Glutamate-binding protein (gene gluB) of Corynebacterium glutamicum.
• Arginine-binding proteins artI and artJ of Escherichia coli.
• Nopaline-binding protein (gene nocT) from Agrobacterium tumefaciens.
• Octopine-binding protein (gene occT) from Agrobacterium tumefaciens.
• Major cell-binding factor (CBF1) (gene: peb1A) from Campylobacter jejuni.
• Bacteroides nodosus protein aabA.
• Cyclohexadienyl/arogenate dehydratase of Pseudomonas aeruginosa, a periplasmic enzyme which forms an alternative pathway for phenylalanine biosynthesis.
• Escherichia coli protein fliY.
• Vibrio harveyi protein patH.
• Escherichia coli hypothetical protein ydhW.
• Bacillus subtilis hypothetical protein yckB.
• Bacillus subtilis hypothetical protein yckK.

The signature pattern is located near the N-terminus of the mature proteins.