A three-dimensional model of human organic anion transporter 1: aromatic amino acids required for substrate transport.
Organic anion transporters (OATs) play a critical role in the handling of endogenous and exogenous organic anions by excretory and barrier tissues. Little is known about the OAT three-dimensional structure or substrate/protein interactions involved in transport. In this investigation, a theoretical three-dimensional model was generated for human OAT1 (hOAT1) based on fold recognition to the crystal structure of the glycerol 3-phosphate transporter (GlpT) from Escherichia coli. GlpT and hOAT1 share several sequence motifs as major facilitator superfamily members. The structural hOAT1 model shows that helices 5, 7, 8, 10, and 11 surround an electronegative putative active site ( approximately 830A(3)). The site opens to the cytoplasm and is surrounded by three residues not previously examined for function (Tyr(230) (domain 5) and Lys(431) and Phe(438) (domain 10)). Effects of these residues on p-aminohippurate (PAH) and cidofovir transport were assessed by point mutations in a Xenopus oocyte expression system. Membrane protein expression was severely limited for the Y230A mutant. For the K431A and F438A mutants, [(3)H]PAH uptake was less than 30% of wild-type hOAT1 uptake after protein expression correction. Reduced V(max) values for the F438A mutant confirmed lower protein expression. In addition, the F438A mutant exhibited an increased affinity for cidofovir but was not significantly different for PAH. Differences in handling of PAH and cidofovir were also observed for the Y230F mutant. Little uptake was determined for cidofovir, whereas PAH uptake was similar to wild-type hOAT1. Therefore, the hOAT1 structural model has identified two new residues, Tyr(230) and Phe(438), which are important for substrate/protein interactions.
Perry
Jennifer L
JL
Laboratory of Pharmacology and Chemistry, NIEHS, National Institutes of Health, Research Triangle Park, North Carolina 27709, USA.
Dembla-Rajpal
Neetu
N
Hall
Laura A
LA
Pritchard
John B
JB
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D024322:Amino Acids, Aromatic / Q000737:chemistry; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D017931:DNA Primers / Q000235:genetics; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009865:Oocytes / Q000378:metabolism; D027362:Organic Anion Transport Protein 1 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D055672:Static Electricity; D014982:Xenopus laevis
D024322:Amino Acids, Aromatic; D017931:DNA Primers; D027362:Organic Anion Transport Protein 1; D011994:Recombinant Proteins