title: Mutagenesis and cysteine scanning of transmembrane domain 10 of the human dipeptide transporter.
abstract: OBJECTIVE
  The human dipeptide transporter (hPEPT1) facilitates transport of dipeptides and drugs from the intestine into the circulation. The role of transmembrane domain 10 (TMD10) of hPEPT1 in substrate translocation was investigated using cysteine-scanning mutagenesis with 2-Trimethylammonioethyl methanethiosulfonate (MTSET).
  
  
  METHODS
  Each amino acid in TMD10 was mutated individually to cysteine, and transport of [(3)H]Gly-Sar was evaluated with and without MTSET following transfection of each mutant in HEK293 cells. Similar localization and expression levels of wild type (WT) hPEPT1 and all mutants were confirmed by immunostaining and biotinylation followed by western blot analysis.
  
  
  RESULTS
  E595C- and G594C-hPEPT1 showed negligible Gly-Sar uptake. E595D-hPEPT1 showed similar uptake to WT-hPEPT1, but E595K- and E595R-hPEPT1 did not transport Gly-Sar. Double mutations E595K/R282E and E595R/R282E did not restore uptake. G594A-hPEPT1 showed similar uptake to WT-hPEPT1, but G594V-hPEPT1 eliminated uptake. Y588C-hPEPT1 showed uptake of 20% that of WT-hPEPT1. MTSET modification supported a model of TMD10 with an amphipathic helix from I585 to V600 and increased solvent accessibility from T601 to F605.
  
  
  CONCLUSIONS
  Our results suggest that G594 and E595 in TMD10 of hPEPT1 have key roles in substrate transport and that Y588 may have an important secondary mechanistic role.
authors.affiliation: Alcohol and Brain Research Laboratory, Titus Family Department of Clinical Pharmacy and Pharmaceutical Economics & Policy, School of Pharmacy, University of Southern California, Los Angeles, California 90033, USA.
authors.forename: Liya
authors.initials: L
authors.lastname: Xu
authors.forename: Ian S
authors.initials: IS
authors.lastname: Haworth
authors.forename: Ashutosh A
authors.initials: AA
authors.lastname: Kulkarni
authors.forename: Michael B
authors.initials: MB
authors.lastname: Bolger
authors.forename: Daryl L
authors.initials: DL
authors.lastname: Davies
mesh_terms: D019943:Amino Acid Substitution / Q000235:genetics*; D002460:Cell Line; D002462:Cell Membrane / Q000737:chemistry / Q000235:genetics; D003545:Cysteine / Q000737:chemistry / Q000235:genetics*; D004151:Dipeptides / Q000737:chemistry / Q000235:genetics*; D005110:Extracellular Space / Q000737:chemistry / Q000235:genetics; D018698:Glutamic Acid / Q000737:chemistry / Q000235:genetics; D005998:Glycine / Q000737:chemistry / Q000235:genetics; D006801:Humans; D016297:Mutagenesis, Site-Directed; D000074011:Peptide Transporter 1; D017434:Protein Structure, Tertiary / Q000235:genetics; D021381:Protein Transport / Q000235:genetics; D027981:Symporters / Q000737:chemistry / Q000235:genetics*; D014443:Tyrosine / Q000737:chemistry / Q000235:genetics
chemical_list: D004151:Dipeptides; D000074011:Peptide Transporter 1; C082186:SLC15A1 protein, human; D027981:Symporters; D018698:Glutamic Acid; D014443:Tyrosine; D003545:Cysteine; D005998:Glycine
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