Microbiology (1 997), 143, 387-396 Printed in Great Britain An oligopeptide transport gene from Candida albicans Mark A. Lubkowitz,’ Loren Hauser,’ Michael Bre~lav,~ Fred Naider3 and Jeffrey M. Beckerl Author for correspondence : Jeffrey M. Becker. Tel : + 1 423 974 3006. Fax : + 1 423 974 4007. e-mail : JBECKER@UTK.EDU Department of Microbiology and Department of Biochemistry, Cellular, and Molecular Biology, University of Tennessee, Knoxville, TN 37996-0845, USA 2 University of Tennessee- Oak Ridge Graduate School of Biomedical Sciences, Biology Division, Oak Ridge National Laboratory, Oak Ridge, 3 Department of Chemistry, College of Staten Island, City University of New York, Staten Island, NY 10314, USA TN 37831-8080, USA A Candida albicans oligopeptide transport gene, OPT7, was cloned from a C. albicans genomic library through heterologous expression in the Saccharomyces cerevisiae di-Rripeptide transport mutant PBlX-9B. When transformed with a plasmid harbouring OPT7, S. cerevisiae PBlX-9B, which did not express tetra-/pentapeptide transport activity under the conditions used, was conferred with an oligopeptide transport phenotype, as indicated by growth on the tetrapeptide Lys-Leu-Leu-Gly, sensitivity to toxic tetra- and pentapeptides, and an increase in the initial uptake rate of the radiolabelled tetrapeptide Lys-Leu-G IY[~H] Leu. The level of ol igopeptide transport was found to be influenced in the heterologous host by the source of nitrogen used for growth. The entire 3.8 kb fragment containing the oligopeptide transport activity was sequenced and an ORF of 2349 nucleotides containing a 58 nucleotide intron was identified. The deduced protein product of 783 amino acid residues contained 12 hydrophobic regions suggestive of a membrane transport protein. Sequence comparisons revealed that similar proteins are encoded by genes from 5. cerevisiae and Schizosaccharomyces pombe and that OPT1 is not a member of the ABC or PTR membrane transport families. INTRODUCTION Keywords : Candida albicans, peptide transport, Saccharomyces cerevisiae Peptide transport, a phenomenon defined as the trans- location of peptides across the plasma membrane in an energy-dependent manner, has been well documented in bacteria, plants, fungi and mammals (for reviews see Becker & Naider, 1995; Payne & Smith, 1994). Upon internalization, peptides are quickly hydrolysed into their amino acid components to serve as sources of amino acids or nitrogen. In addition to acquiring nutrients from the environment, peptide transport has been shown to play a role in recycling cell wall peptides and in transducing signals for group behaviours such as sporulation and competency in Bacillus subtilis and chemotaxis in Escherichia coli. Recently, it has been proposed that in Salmonella typhimurium peptide trans- porters aid the bacteria in evading the host immune response by transporting membrane-disrupting peptides away from the plasma membrane (Parra-Lopez et al., 1993). Similarly, in Streptococcus pneumoniae the pep- tide transporters encoded by plpA and the amiA loci The GenBank accession number for the nucleotide sequence reported in this paper is U60973. play a role in virulence by modulating adherence to epithelial and endothelial cells (Cundell et al., 1995). Our laboratory has recently identified a family of di- /tripeptide transporters named the PTR (Peptide TRansport) family. This family is characterized by several conserved motifs, has 12 putative trans- membrane domains, and is driven by the proton-motive force. Members of the PTR family have been identified in a wide variety of eukaryotes and one prokaryote as well (Steiner et al., 1995). Well-characterized members of the PTR family are the di- and tripeptide transporters from Saccharomyces cerevisiae (ScPTR2 ; Perry et al., 1994) and from Candida albicans (CaPTR2; Basrai et al., 1995). Both CaPTR2 and ScPTR2 are regulated by the nitrogen source and are inducible by micromolar amounts of amino acids; the proteins they encode have broad substrate specificities with a preference for peptides containing hydrophobic residues (Basrai et al., 1992; Island et al., 1987). Prior to the establishment of the PTR family, all peptide transporters cloned were from prokaryotes and were members of the ATP- binding cassette (ABC) superfamily (Higgins, 1992). Recently, transporters from the PTR family have been 0002-1100 0 1997 SGM 387