Cysteine residues in the C-terminus of the neutral- and basic-amino-acid transporter heavy-chain subunit contribute to functional properties of the system b(0,+)-type amino acid transporter.
The neutral- and basic-amino-acid-transport glycoprotein NBAT (rBAT, D2) expressed in renal and jejunal brush-border membranes interacts with the b(0,+)AT permease to produce a heteromeric transporter effecting amino acid and cystine absorption. NBAT mutations result in type I cystinuria. The b(0,+)AT permease is presumed to be the catalytic subunit, but we have been investigating the possibility that cysteine residues within the C-terminus of NBAT are also important for expression of transport function. NBAT mutants were produced with combinations of Cys(664/671/683)-->Ala substitutions. Mutants with Cys(664)-->Ala show decreased arginine and cystine transport and specifically lose sensitivity to inhibition of transport by the thiol-group reagent N-ethylmaleimide (NEM). We suggest that the C-terminus of NBAT may have a direct role in the mechanism of System b(0,+) transport (the major transport activity defective in type I cystinuria) and that Cys(664) of NBAT is the major target for NEM-induced inactivation of the transport mechanism.
Peter
G J
GJ
Department of Anatomy and Physiology, University of Dundee MSI/WTB Complex, Dundee DD1 5EH, Scotland, U.K.
Panova
T B
TB
Christie
G R
GR
Taylor
P M
PM
D000595:Amino Acid Sequence; D026923:Amino Acid Transport Systems, Basic; D026921:Amino Acid Transport Systems, Neutral; D000596:Amino Acids / Q000378:metabolism*; D000818:Animals; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D003545:Cysteine / Q000378:metabolism*; D008969:Molecular Sequence Data; D016296:Mutagenesis; D009865:Oocytes / Q000378:metabolism; D014981:Xenopus
D026923:Amino Acid Transport Systems, Basic; D026921:Amino Acid Transport Systems, Neutral; D000596:Amino Acids; D002352:Carrier Proteins; D003545:Cysteine