Conserved tryptophan residues within putative transmembrane domain 6 affect transport function of organic anion transporting polypeptide 1B1. 2013

Jiujiu Huang, and Nan Li, and Weifang Hong, and Kai Zhan, and Xuan Yu, and Hong Huang, and Mei Hong
College of Life Science, South China Agricultural University, Guangzhou, China (J.H., N.L., W.H., K.Z., X.Y., M.H.); and School of Information, University of South Florida, Tampa, Florida (H.H.).

The organic anion-transporting polypeptides (OATPs, gene symbol SLCO) are a family of transporters that play important roles in the absorption, distribution, metabolism, and excretion of various drugs. Although substrate specificity of transporter proteins is under extensive study, the underlying mechanisms for substrate binding and/or recognition remain largely unknown. Transmembrane domain 6 (TM6) is a relatively conserved region within OATP family members, and several amino acid residues on its extracellular half are part of the OATP family signature sequence D-X-RW-(I,V)-GAWWX-G-(F,L)-L. In the present study, two adjacent tryptophan residues (Trp258 and Trp259) within TM6 were identified as critical amino acids for the transport function of OATP1B1. Kinetic studies showed that substitution of Trp258 with alanine resulted in monophasic kinetics for estrone-3-sulfate uptake, with a significantly higher Km value (Km = 12.0 ± 2.8 μM) than the high-affinity component of wild-type OATP1B1 (Km = 0.38 ± 0.06 μM). On the other hand, W259A retained the biphasic characteristic of the transporter. Km values of the high- and low-affinity components for estrone-3-sulfate of W259A are 1.93 ± 0.76 μM and 30.8 ± 4.4 μM, respectively. Further studies revealed that W258A retained transport function of another prototypic substrate, taurocholate, while W259A displayed a dramatically reduced uptake of the substrate and exhibited an 8-fold increase in the Km value compared with that of the wild-type and W258A. Our results suggest that Trp258 and Trp259 may play different roles in the uptake of different substrates by OATP1B1.

UI MeSH Term Description Entries
D008969 Molecular Sequence Data Descriptions of specific amino acid, carbohydrate, or nucleotide sequences which have appeared in the published literature and/or are deposited in and maintained by databanks such as GENBANK, European Molecular Biology Laboratory (EMBL), National Biomedical Research Foundation (NBRF), or other sequence repositories. Sequence Data, Molecular,Molecular Sequencing Data,Data, Molecular Sequence,Data, Molecular Sequencing,Sequencing Data, Molecular
D002462 Cell Membrane The lipid- and protein-containing, selectively permeable membrane that surrounds the cytoplasm in prokaryotic and eukaryotic cells. Plasma Membrane,Cytoplasmic Membrane,Cell Membranes,Cytoplasmic Membranes,Membrane, Cell,Membrane, Cytoplasmic,Membrane, Plasma,Membranes, Cell,Membranes, Cytoplasmic,Membranes, Plasma,Plasma Membranes
D006801 Humans Members of the species Homo sapiens. Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D000595 Amino Acid Sequence The order of amino acids as they occur in a polypeptide chain. This is referred to as the primary structure of proteins. It is of fundamental importance in determining PROTEIN CONFORMATION. Protein Structure, Primary,Amino Acid Sequences,Sequence, Amino Acid,Sequences, Amino Acid,Primary Protein Structure,Primary Protein Structures,Protein Structures, Primary,Structure, Primary Protein,Structures, Primary Protein
D014364 Tryptophan An essential amino acid that is necessary for normal growth in infants and for NITROGEN balance in adults. It is a precursor of INDOLE ALKALOIDS in plants. It is a precursor of SEROTONIN (hence its use as an antidepressant and sleep aid). It can be a precursor to NIACIN, albeit inefficiently, in mammals. Ardeydorm,Ardeytropin,L-Tryptophan,L-Tryptophan-ratiopharm,Levotryptophan,Lyphan,Naturruhe,Optimax,PMS-Tryptophan,Trofan,Tryptacin,Tryptan,Tryptophan Metabolism Alterations,ratio-Tryptophan,L Tryptophan,L Tryptophan ratiopharm,PMS Tryptophan,ratio Tryptophan
D017124 Conserved Sequence A sequence of amino acids in a polypeptide or of nucleotides in DNA or RNA that is similar across multiple species. A known set of conserved sequences is represented by a CONSENSUS SEQUENCE. AMINO ACID MOTIFS are often composed of conserved sequences. Conserved Sequences,Sequence, Conserved,Sequences, Conserved
D017433 Protein Structure, Secondary The level of protein structure in which regular hydrogen-bond interactions within contiguous stretches of polypeptide chain give rise to ALPHA-HELICES; BETA-STRANDS (which align to form BETA-SHEETS), or other types of coils. This is the first folding level of protein conformation. Secondary Protein Structure,Protein Structures, Secondary,Secondary Protein Structures,Structure, Secondary Protein,Structures, Secondary Protein
D017434 Protein Structure, Tertiary The level of protein structure in which combinations of secondary protein structures (ALPHA HELICES; BETA SHEETS; loop regions, and AMINO ACID MOTIFS) pack together to form folded shapes. Disulfide bridges between cysteines in two different parts of the polypeptide chain along with other interactions between the chains play a role in the formation and stabilization of tertiary structure. Tertiary Protein Structure,Protein Structures, Tertiary,Tertiary Protein Structures
D057809 HEK293 Cells A cell line generated from human embryonic kidney cells that were transformed with human adenovirus type 5. 293T Cells,HEK 293 Cell Line,HEK 293 Cells,Human Embryonic Kidney Cell Line 293,Human Kidney Cell Line 293,293 Cell, HEK,293 Cells, HEK,293T Cell,Cell, 293T,Cell, HEK 293,Cell, HEK293,Cells, 293T,Cells, HEK 293,Cells, HEK293,HEK 293 Cell,HEK293 Cell
D021381 Protein Transport The process of moving proteins from one cellular compartment (including extracellular) to another by various sorting and transport mechanisms such as gated transport, protein translocation, and vesicular transport. Cellular Protein Targeting,Gated Protein Transport,Protein Targeting, Cellular,Protein Translocation,Transmembrane Protein Transport,Vesicular Protein Transport,Protein Localization Processes, Cellular,Protein Sorting,Protein Trafficking,Protein Transport, Gated,Protein Transport, Transmembrane,Protein Transport, Vesicular,Traffickings, Protein

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