title: Wide tolerance to amino acids substitutions in the OCTN1 ergothioneine transporter.
abstract: BACKGROUND
  Organic cation transporters transfer solutes with a positive charge across the plasma membrane. The novel organic cation transporter 1 (OCTN1) and 2 (OCTN2) transport ergothioneine and carnitine, respectively. Mutations in the SLC22A5 gene encoding OCTN2 cause primary carnitine deficiency, a recessive disorders resulting in low carnitine levels and defective fatty acid oxidation. Variations in the SLC22A4 gene encoding OCTN1 are associated with rheumatoid arthritis and Crohn disease.
  
  
  METHODS
  Here we evaluate the functional properties of the OCTN1 transporter using chimeric transporters constructed by fusing different portion of the OCTN1 and OCTN2 cDNAs. Their relative abundance and subcellular distribution was evaluated through western blot analysis and confocal microscopy.
  
  
  RESULTS
  Substitutions of the C-terminal portion of OCTN1 with the correspondent residues of OCTN2 generated chimeric OCTN transporters more active than wild-type OCTN1 in transporting ergothioneine. Additional single amino acid substitutions introduced in chimeric OCTN transporters further increased ergothioneine transport activity. Kinetic analysis indicated that increased transport activity was due to an increased V(max), with modest changes in K(m) toward ergothioneine.
  
  
  CONCLUSIONS
  Our results indicate that the OCTN1 transporter is tolerant to extensive amino acid substitutions. This is in sharp contrast to the OCTN2 carnitine transporter that has been selected for high functional activity through evolution, with almost all substitutions reducing carnitine transport activity.
  
  
  CONCLUSIONS
  The widespread tolerance of OCTN1 to amino acid substitutions suggests that the corresponding SLC22A4 gene may have derived from a recent duplication of the SLC22A5 gene and might not yet have a defined physiological role.
authors.affiliation: Division of Medical Genetics, Departments of Pediatrics and Pathology, University of Utah, Salt Lake City, UT 84108, United States.
authors.forename: Marta
authors.initials: M
authors.lastname: Frigeni
authors.affiliation: Division of Medical Genetics, Departments of Pediatrics and Pathology, University of Utah, Salt Lake City, UT 84108, United States; Department of Basic Medical Sciences, University of Bari, Policlinico, I-70124 Bari, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Iacobazzi
authors.affiliation: Division of Medical Genetics, Departments of Pediatrics and Pathology, University of Utah, Salt Lake City, UT 84108, United States.
authors.forename: Xue
authors.initials: X
authors.lastname: Yin
authors.affiliation: Division of Medical Genetics, Departments of Pediatrics and Pathology, University of Utah, Salt Lake City, UT 84108, United States. Electronic address: Nicola.Longo@hsc.utah.edu.
authors.forename: Nicola
authors.initials: N
authors.lastname: Longo
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D001692:Biological Transport; D015153:Blotting, Western; D016466:CHO Cells; D003412:Cricetulus; D004880:Ergothioneine / Q000493:pharmacokinetics*; D006801:Humans; D018613:Microscopy, Confocal; D027701:Organic Cation Transport Proteins / Q000737:chemistry / Q000502:physiology*; D013329:Structure-Activity Relationship; D027981:Symporters
chemical_list: D027701:Organic Cation Transport Proteins; C109807:SLC22A4 protein, human; D027981:Symporters; D004880:Ergothioneine
keywords: Ergothioneine transport; OCTN1; OCTN2; Organic cation transporters; SLC22A4; SLC22A5