title: Restricted motion of the conserved immunoglobulin G1 N-glycan is essential for efficient FcγRIIIa binding.
abstract: Immunoglobulin G1 (IgG1)-based therapies are widespread, and many function through interactions with low-affinity Fc γ receptors (FcγR). N-glycosylation of the IgG1 Fc domain is required for FcγR binding, though it is unclear why. Structures of the FcγR:Fc complex fail to explain this because the FcγR polypeptide does not bind the N-glycan. Here we identify a link between motion of the N-glycan and Fc:FcγRIIIa affinity that explains the N-glycan requirement. Fc F241 and F243 mutations decreased the N-glycan/polypeptide interaction and increased N-glycan mobility. The affinity of the Fc mutants for FcγRIIIa was directly proportional to the degree of glycan restriction (R(2) = 0.82). The IgG1 Fc K246F mutation stabilized the N-glycan and enhanced affinity for FcγRIIIa. Allosteric modulation of a protein/protein interaction represents a previously undescribed role for N-glycans in biology. Conserved features suggesting a similar N-glycan/aromatic interaction were also found in IgD, IgE, and IgM, but not IgA.
authors.affiliation: Roy J. Carver Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames, IA 50011, USA.
authors.forename: Ganesh P
authors.initials: GP
authors.lastname: Subedi
authors.affiliation: Roy J. Carver Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames, IA 50011, USA.
authors.forename: Quinlin M
authors.initials: QM
authors.lastname: Hanson
authors.affiliation: Roy J. Carver Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames, IA 50011, USA. Electronic address: abarb@iastate.edu.
authors.forename: Adam W
authors.initials: AW
authors.lastname: Barb
mesh_terms: D000117:Acetylglucosamine / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D007072:Immunoglobulin D / Q000737:chemistry / Q000378:metabolism; D007073:Immunoglobulin E / Q000737:chemistry / Q000378:metabolism; D007141:Immunoglobulin Fc Fragments / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D007074:Immunoglobulin G / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D007075:Immunoglobulin M / Q000737:chemistry / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D009154:Mutation; D011134:Polysaccharides / Q000737:chemistry; D011485:Protein Binding; D011487:Protein Conformation; D017510:Protein Folding; D017452:Receptors, IgG / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D007072:Immunoglobulin D; D007141:Immunoglobulin Fc Fragments; D007074:Immunoglobulin G; D007075:Immunoglobulin M; D011134:Polysaccharides; D017452:Receptors, IgG; D007073:Immunoglobulin E; D000117:Acetylglucosamine