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 complete deglycosylation during the process of protein maturation. In order to elucidate the site of glycosylation and its role in rhodopsin synthesis, we investigated the in vitro and in vivo synthesis of rhodopsin whose 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-terminal extracellular domain. Furthermore, the results gave the first evidence directly indicating that deletion of the oligosaccharide chain markedly impedes rhodopsin maturation.