Effect of the sugar chain of soluble recombinant CD59 on complement inhibitory activity

Abstract

A soluble recombinant CD59no77 (rCD59no77), consisting of 77 amino acids starting from the N terminus of membrane-bound CD59, was prepared using a gene expression system in CHO cells. The rCD59no77 preparation was composed of glycosylated and non-glycosylated forms (G and NG forms). Unexpectedly, NG form was 7 times more potent than G form in complement inhibitory activity. Postulating that sialic acids on G-form molecules make it difficult for rCD59no77 to access nascent membrane attack complexes on the cell surface, the sialic acids were removed by neuraminidase treatment. However, the inhibitory activity was not changed. Next, one of two putative N-glycosylation sites was mutated by substituting Gln18 for Asn18. The mutant, designated rCD59no77(N/Q), had no sugar moiety and was as active as the NG form of rCD59no77. These results suggest that the bulky sugar moiety at Asn18 is not necessary for the complement-inhibitory activity of rCD59 and actually hampers that function.