Dynamic inter-glycan interactions regulate site-specific N-glycan maturation in human Fcγ receptor III.

Protein N-glycosylation generates diverse glycoforms that influence protein structure and function, yet the molecular rules governing site-specific glycan maturation remain incompletely understood. Accumulating evidence indicates that glycosylation outcomes are shaped by determinants embedded within glycoproteins themselves, beyond enzyme availability alone. Here, we investigate how neighboring glycans modulate site-specific N-glycan maturation in human Fcγ receptor III (FcγRIII). Building on previous glycoproteomic studies showing restricted processing of the N45 glycan in FcγRIII molecules, we combined reciprocal glycosylation-site mutagenesis with molecular dynamics simulations. Introduction of an N64 glycosylation sequon into FcγRIIIa reduced N45 glycan maturation, whereas removal of the N64 sequon from FcγRIIIb produced the reciprocal effect. Simulations using glycan models, analyzed primarily by contact maps and contact frequencies, showed that the N45 glycan dynamically contacts neighboring N64 and N169 glycans. These findings support a model in which the isoform-specific N64 glycan, in addition to the adjacent N169 glycan shared by both FcγRIII isoforms, contributes to reduced N45 glycan maturation by reshaping the local glycan environment around N45.