FUNCTIONAL HETERODIMERIC AMINO-ACID TRANSPORTERS LACKING CYSTEINE RESIDUES INVOLVED IN DISULFIDE BOND

The protein mediating system L amino acid transport, AmAT-L, is a disu lfide-linked heterodimer of a permease-related light chain (AmAT-L-lc) and the type II glycoprotein 4F2hc/ CD98, The Schistosoma mansoni pro tein SPRM1 also heterodimerizes with h4F2hc, inducing amino acid trans port with different specificity. In this study, we show that the disul fide bond is formed by heavy chain C109 with a Cys residue located in the second putative extracellular loop of the multi-transmembrane doma in light chain (C164 and C137 for XAmAT-L-lc and SPRM1, respectively). The non-covalent interaction of Cys-mutant subunits is not sufficient to allow coimmunoprecipitation, but cell surface expression of the li ght chains is maintained to a large extent, The non-covalently linked transporters display the same transport characteristics as disulfide b ound heterodimers, but the maximal transport rates are reduced by 30-8 0%. (C) 1998 Federation of European Biochemical Societies.