Structural and functional characterization of glycosylation in an immunoglobulin G1 to Cryptococcus neoformans glucuronoxylomannan

Analysis of the N-linked oligosaccharides of the murine IgG I monoclonal antibody (mAb) to Cryptococcus neofomans by LC/MS revealed five different core fucosylated, biantennary complex-type oligosaccharides at Asn-293, with the major species being a mono-galactosylated oligosaccharide with the glycosyl composition of Hex(4)HexNAc(4)Fuc (39% of the total glycan pool). The primary sequence predicted from nucleic acid sequencing differed from that measured by mass spectrometry at position 33 (ASN to ASP), a finding that may represent posttranslational modification caused by spontaneous ASP deamination. Analysis of mAb 18B7 from three hybridoma clones revealed the same heterogenous N-glycan pattern, indicating that diversity in oligosaccharide Structures originated from individual cells. The binding of native and de-glycosylated mAb 18B7 to cryptococcal A, was comparable but the de-glycosylated 18B7 had shorter serum half-life and did not activate complement (Q. De-glycosylated mAb 18B7 was opsonic for C. neoformans with murine macrophages through a mechanism that involved C-independent ingestion through the C receptor. Passive administration of de-glycosylated mAb 18B7 mediated comparable protective efficacy to the native mAb in mice with lethal infection. The results imply that the contribution of N-glycan Structure to immunoglobulin function varies depending on the Ag-Ab system. (C) 2005 Published by Elsevier Ltd.