Proteins of the Proton-dependent Oligopeptide Transporter (POT) Family (also called the PTR (peptide transport) family) are found in animals, plants, yeast, archaea and both Gram-negative and Gram-positive bacteria, and are part of the major facilitator superfamily. The transport of peptides into cells is a well-documented biological phenomenon which is accomplished by specific, energy-dependent transporters found in a number of organisms as diverse as bacteria and humans. The proton-dependent oligopeptide transporter (PTR) family of proteins is distinct from the ABC-type peptide transporters and was uncovered by sequence analyses of a number of recently discovered peptide transport proteins.[1] These proteins that seem to be mainly involved in the intake of small peptides with the concomitant uptake of a proton.[2]
While most members of the POT family catalyze peptide transport, one is a nitrate permease and one can transport histidine, as well as peptides. Some of the peptide transporters can also transport antibiotics. They function by proton symport, but the substrate:H+ stoichiometry is variable: the high-affinity rat PepT2 carrier catalyzes uptake of 2 and 3 H+ with neutral and anionic dipeptides, respectively, while the low affinity PepT1 carrier catalyzes uptake of one H+ per neutral peptide.[3] [4]
The generalized transport reaction catalyzed by the proteins of the POT family is:
substrate (out) + H (out) → substrate (in) H+ (in)
The proteins are of about 450-600 amino acyl residues in length with the eukaryotic proteins in general being longer than the bacterial proteins. They exhibit 12 putative or established transmembrane α-helical spanners.
Pairs of salt bridge interactions between transmembrane helices work in tandem to orchestrate alternating access transport within the PTR family.[5] Key roles for residues conserved between bacterial and eukaryotic homologues suggest a conserved mechanism of peptide recognition and transport that in some cases has been subtly modified in individual species.
FP12591