Family 2.A.67 - The Oligopeptide Transporter Family       

Family ID: 52643

The OPT family consists of functionally well characterized oligopeptide (3-6 amino acid) transporters in yeast. One of the yeast homologues is the sexual differentiation process (ISP4) protein of Schizosaccharomyces pombe. S. cerevisiae and S. pombe each possesses three paralogues of the OPT family. Two transporter from S. cerevisiae, one from S. pombe, and one from Candida albicans have been functionally characterized, and all are peptide uptake systems. Homologues are also found in plants, bacteria and archaea. The prokaryotic homologues are very distant, being revealed only upon PSI-BLAST iterations, and they are also uncharacterized functionally. Energy coupling probable involves H+ symport.

The full length yeast proteins are reported to be 700-900 residues long and exhibit 12 putative TMSs. A bacterial homologue from H. influenzae is 633 amino acyl residues long and exhibits 15 putative TMSs. An Fe3+-phytosiderophore uptake system of Zea mays, also known as "yellow stripe1" (YS1) is encoded by the ys1 gene, the expression of which is increased in both roots and shoots under iron deficient conditions (Curie et al, 2001). When expressed in a mutant yeast lacking its native iron uptake system, it corrects the defect specifically in Fe3+-phytosiderophore media.

Nine genes (designated YS-like genes 1-9 or YS1-9) in Arabidopsis thaliana encode close homologues of YS1 (Curie et al, 2001). These proteins and nine other distant OPT family homologues are of about the same size (about 600aas and exhibit 12-13 putative TMSs. YS1 has a glutamine-rich N-terminus that might function in Fe3+ binding. Some of these plant proteins may be more similar to the bacterial and archaeal homologues than to the yeast peptide porters.