Characterization of N-linked oligosaccharides attached to human renin expressed in COS cells

To study the role of N-linked oligosaccharides attached to human renin, we generated three kinds of glycosylation-deficient renins in which one or both of two putative N-glycosylation sites was eliminated by amino acid replacement using site-directed mutagenesis. Examination of the three mutant renins (Asn-5 to Ala, Asn-75 to Ala, and both Asn-5 and -75 to Ala) expressed in COS cells demonstrated that both putative sites were certainly glycosylated with heterologous N-linked oligosaccharides. Moreover, the oligosaccharide chain attached at Asn-5 was different from that attached at Asn-75 in its molecular size. In addition, the secreted amount of the three mutant renins were different from one another, although the mutant and wild-type renins had practically the same specific activity. Our results suggest that the N-linked oligosaccharides have no effect on the enzymatic activity, but play an important role in stable secretion of human renin.