2.A.67 The Oligopeptide Transporter (OPT) Family 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 possess three paralogues of the OPT family. Two transporters 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. YS1 has a glutamine-rich N-terminus that might function in Fe³⁺ binding. It has been shown to be a proton symporter that takes up phytosiderophore- and nicotianamine-chelated metals (Schaaf et al., 2003). Note: Nicotianamine is a structural analogue of phytosiderophores and is also an intracellular metal chelator. 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 600 aas) 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. The generalized transport reactions thought to be catalyzed by members of the OPT family are: 1) Oligopeptide (out) + nH⁺ (out) → oligopeptide (in) + nH⁺ (in). 2) Fe³⁺-phytosiderophore (out) + H⁺ (out)? → Fe³⁺-phytosiderophore (in) + H⁺ (in)
References:
Bourbouloux, A., P. Shahi, A. Chakladar, S. Delrot, and A.K. Bachhawat. (2000). Hgt1p, a high affinity glutathione transporter from the yeast Saccharomyces cerevisiae. J. Biol. Chem. 275: 13259-13265.
Cho, K. and D.R. Zusman. (1999). Sporulation timing in Myxococcus xanthus is controlled by the espAB locus. Mol. Microbiol. 34: 714-725.
Curie, C., Z. Panaviene, C. Loulergue, S.L. Dellaporta, J-F Briat, and E.L. Walker. (2001). Maize yellow stripe1 encodes a membrane protein directly involved in Fe(III) uptake. Nature 409: 346-349.
Hauser, M., A.M. Donhardt, D. Barnes, F. Naider, and J.M. Becker. (2000). Enkephalins are transported by a novel eukaryotic peptide uptake system. J. Biol. Chem. 275: 3037-3041.
Hauser, M., V. Narita, A.M. Donhardt, F. Naider, and J.M. Becker. (2001). Multiplicity and regulation of genes encoding peptide transporters in Saccharomyces cerevisiae. Mol. Membr. Biol. 18: 105-112.
Lubkowitz, M.A., D. Barnes, M. Breslav, A. Burchfield, F. Naider, and J.M. Becker. (1998). Schizosaccharomyces pombe isp4 encodes a transporter representing a novel family of oligopeptide transporters. Mol. Microbiol. 28: 729-741.
Lubkowitz, M.A., L. Hauser, M. Breslav, F. Naider, and J.M. Becker. (1997). An oligopeptide transport gene from Candida albicans. Microbiology 143: 387-396.
Sato, S., H. Suzuki, U. Widyastuti, Y. Hotta, and S. Tabatta. (1994). Identification and characterization of genes induced during sexual differentiation in Schizosaccharomyces pombe. Curr. Genet. 26: 31-37.
Schaaf, G., U. Ludewig, B.E. Erenoglu, S. Mori, T. Kitahara, and N. von Wirén. (2004). ZmYS1 functions as a proton-coupled symporter for phytosiderophore- and nicotianamine-chelated metals. J. Biol. Chem. 279: 9091-9096.
Yen, M.-R., Y.-H. Tseng, and M.H. Saier, Jr. (2001). Maize Yellow Stripe1, an iron-phytosiderophore uptake transporter, is a member of the oligopeptide transporter (OPT) family. Microbiology 147: 2882-2883.
Examples:
TC#	Name	Organismal Type	Example
2.A.67.1.1	Oligopeptide transporter, OPT1	Yeast	OPT1 of Candida albicans

2.A.67.1.2	Sexual differentiation process, ISP4 protein (tetra peptide transporter)	Yeast	ISP4 of Schizosaccharomyces pombe

2.A.67.1.3	The YJL212c gene protein (oligopeptide transporter, Opt1p; transports the mammalian pentapeptide, enkephalin, and the tripeptide, glutathione)	Yeast	Opt1p (YJL212c) of Saccharomyces cerevisiae

2.A.67.1.4	The YPR194c gene protein (oligopeptide transporter, Opt2p)	Yeast	Opt2p (YPR194c) of Saccharomyces cerevisiae

2.A.67.2.1	'Yellow Stripe1' (YS1) Fe³⁺-phyto siderophore:H⁺ symporter. It takes up various metal cations (Fe³⁺, Zn²⁺, Cu²⁺, Ni²⁺, Mn²⁺ and Cd²⁺ when complexed with phytosiderophores, and Ni²⁺, Fe²⁺ and Fe³⁺ when complexed with nicotinamine) (Curie et al., 2001; Schaaf et al., 2004)	Plants	YS1 of Zea mays

2.A.67.3.1	Early sporulation protein, EspB (temporal control protein)	Bacteria	EspB of Myxococcus xanthus

2.A.67.4.1	Orf HI0561/560	Bacteria	Orf of Haemophilus influenzae