N-LINKED GLYCOSYLATION OF DROSOPHILA RHODOPSIN OCCURS EXCLUSIVELY IN THE AMINO-TERMINAL DOMAIN AND FUNCTIONS IN RHODOPSIN MATURATION

Immature Drosophila rhodopsin is N-glycosylated, but undergoes complet e deglycosylation during the process of protein maturation. In order t o elucidate the site of glycosylation and its role in rhodopsin synthe sis, we investigated the in vitro and in vivo synthesis of rhodopsin w hose putative N-glycosylation sites (Asn-20 and Asn-196) were replaced by isoleucine. The results demonstrated that immature rhodopsin binds a single oligosaccharide chain exclusively at Asn-20 in the N-termina l extracellular domain. Furthermore, the results gave the first eviden ce directly indicating that deletion of the oligosaccharide chain mark edly impedes rhodopsin maturation. (C) 1998 Federation of European Bio chemical Societies.