title: Mitochondrial phosphate transport. Import of the H+/Pi symporter and role of the presequence.
abstract: The rat liver mitochondrial phosphate transporter contains a 44-amino acid presequence. The role of this presequence is not clear since the ADP/ATP carrier and the brown fat uncoupling protein, related members of a family of inner membrane anion transporters, lack a presequence and contain targeting information within the mature protein. Here, we present evidence that the rat liver mitochondrial phosphate transporter can be synthesized in vitro, imported into mitochondria, and processed to a protein of Mr 33,000. Import requires the membrane potential and external nucleotide triphosphate. The presequence inserts into the outer mitochondrial membrane, and import proceeds via a process similar to other proteins destined for the inner membrane or matrix. A mutant phosphate transporter lacking 35 amino acids at the NH2 terminus of the presequence has little capacity for mitochondrial import. The rat liver phosphate transporter is also imported and processed by rat kidney mitochondria and by mitochondria from the yeast Saccharomyces cerevisiae. A site-directed mutation of the N-ethyl-maleimide reactive cysteine 41 does not affect import or processing. The results presented show that optimal import of the mitochondrial phosphate transporter, unlike the ADP/ATP carrier and the brown fat uncoupling protein, is dependent on a presequence. As these carriers are believed to have evolved from a single gene, it seems likely that the H+/Pi carrier, known to be present in prokaryotes, appeared first and that subsequent evolutionary events leading to the other anion carriers eliminated the presequence.
authors.affiliation: Department of Biological Chemistry, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.
authors.forename: R D
authors.initials: RD
authors.lastname: Pratt
authors.forename: G C
authors.initials: GC
authors.lastname: Ferreira
authors.forename: P L
authors.initials: PL
authors.lastname: Pedersen
mesh_terms: D019297:2,4-Dinitrophenol; D000595:Amino Acid Sequence; D000818:Animals; D001692:Biological Transport; D002352:Carrier Proteins / Q000235:genetics*; D004140:Dinitrophenols / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D007668:Kidney / Q000187:drug effects / Q000378:metabolism; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D008930:Mitochondria, Liver / Q000187:drug effects / Q000378:metabolism*; D008969:Molecular Sequence Data; D028044:Phosphate-Binding Proteins; D010710:Phosphates / Q000378:metabolism*; D010957:Plasmids; D014176:Protein Biosynthesis; D051381:Rats; D014158:Transcription, Genetic; D014634:Valinomycin / Q000494:pharmacology; D015003:Yeasts / Q000187:drug effects / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D004140:Dinitrophenols; D028044:Phosphate-Binding Proteins; D010710:Phosphates; D014634:Valinomycin; D019297:2,4-Dinitrophenol