title: Amino Acid Residues in the Putative Transmembrane Domain 11 of Human Organic Anion Transporting Polypeptide 1B1 Dictate Transporter Substrate Binding, Stability, and Trafficking.
abstract: Organic anion transporting polypeptides (OATPs, gene symbol SLCO) are membrane proteins that mediate the sodium-independent transport of a wide range of endogenous and exogenous compounds. Due to their broad substrate specificity, wide tissue distribution, and involvement in drug-drug interactions, OATPs have been considered as key players in drug absorption, distribution, and excretion. Transmembrane domains (TMs) are crucial structural features involved in proper functions of many transporters. According to computer-based modeling and previous studies of our laboratory and others, TM11 of OATP1B1 may face the substrate interaction pocket and thus play an important role in the transport function of the protein. Alanine-scanning of the transmembrane domain identified seven critical amino acid residues within the region. Further analysis revealed that alanine substitution of these residues resulted in reduced protein stability, which led to significantly decreased protein expression on the plasma membrane. In addition, all mutants exhibited an altered Km for ES uptake (either high affinity or low affinity component, or both), though Km for taurocholate transport only changed in R580A, G584A, and F591A. These results suggested that critical residues in TM11 not only affect protein stability of the transporter, but its interaction with substrates as well. The identification of seven essential residues out of 21 TM amino acids highlighted the importance of this transmembrane domain in the proper function of OATP1B1.
authors.affiliation: College of Life Science, South China Agricultural University , Guangzhou, China.
authors.forename: Weifang
authors.initials: W
authors.lastname: Hong
authors.affiliation: College of Life Science, South China Agricultural University , Guangzhou, China.
authors.forename: Zhixuan
authors.initials: Z
authors.lastname: Wu
authors.affiliation: College of Life Science, South China Agricultural University , Guangzhou, China.
authors.forename: Zihui
authors.initials: Z
authors.lastname: Fang
authors.affiliation: College of Life Science, South China Agricultural University , Guangzhou, China.
authors.forename: Jiujiu
authors.initials: J
authors.lastname: Huang
authors.affiliation: School of Information, University of South Florida , Tampa, Florida 33620, United States.
authors.forename: Hong
authors.initials: H
authors.lastname: Huang
authors.affiliation: College of Life Science, South China Agricultural University , Guangzhou, China.
authors.forename: Mei
authors.initials: M
authors.lastname: Hong
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000378:metabolism*; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D007700:Kinetics; D027381:Liver-Specific Organic Anion Transporter 1; D008969:Molecular Sequence Data; D027361:Organic Anion Transporters / Q000378:metabolism*; D010455:Peptides / Q000378:metabolism; D011485:Protein Binding / Q000502:physiology*; D017434:Protein Structure, Tertiary; D021381:Protein Transport / Q000502:physiology*; D013379:Substrate Specificity
chemical_list: D000596:Amino Acids; D027381:Liver-Specific Organic Anion Transporter 1; D027361:Organic Anion Transporters; D010455:Peptides; C503999:SLCO1B1 protein, human
keywords: organic anion transporting polypeptides; transmembrane domains; transporter proteins; uptake function