Cysteine residues in the C-terminus of the neutral- and basic-amino-acid transporter heavy-chain subunit contribute to functional properties of the system b0,+-type amino acid transporter

摘要

pThe bn/beutral- and bb/basic-ba/bmino-acid-bt/bransport glycoprotein NBAT (rBAT, D2) expressed in renal and jejunal brush-border membranes interacts with the bsup0,+/supAT permease to produce a heteromeric transporter effecting amino acid and cystine absorption. NBAT mutations result in type I cystinuria. The bsup0,+/supAT 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 Cyssup664/671/683/sup → Ala substitutions. Mutants with Cyssup664/sup → Ala show decreased arginine and cystine transport and specifically lose sensitivity to inhibition of transport by the thiol-group reagent iN/i-ethylmaleimide (NEM). We suggest that the C-terminus of NBAT may have a direct role in the mechanism of System bsup0,+/sup transport (the major transport activity defective in type I cystinuria) and that Cyssup664/sup of NBAT is the major target for NEM-induced inactivation of the transport mechanism./p