Carbohydrate-Polypeptide Contacts in the Antibody Receptor CD16A Identified through Solution NMR Spectroscopy

Biochemistry. 2017 Jun 27;56(25):3174-3177. doi: 10.1021/acs.biochem.7b00392. Epub 2017 Jun 16.

Abstract

Asparagine-linked carbohydrates (N-glycans) are common modifications of eukaryotic proteins that confer multiple properties, including the essential stabilization of therapeutic monoclonal antibodies. Here we present a rapid and efficient strategy for identifying N-glycans that contact polypeptide residues and apply the method to profile the five N-glycans attached to the human antibody receptor CD16A (Fc γ receptor IIIA). Human embryonic kidney 293S cells expressed CD16A with 13CU-labeled N-glycans using standard protein expression techniques and medium supplemented with 3 g/L [13CU]glucose. Anomeric resonances on the protein-linked N-acetylglucosamine residue at the reducing end of the glycan are particularly well suited to studies of multiply glycosylated N-glycoproteins because only one reducing end and nitrogen-linked residue is present in each N-glycan. Correlations between anomeric 1H1 and 13C1 nuclei on the reducing end residue generate crosspeaks in a conventional two-dimensional heteronuclear single-quantum coherence nuclear magnetic resonance (NMR) experiment that appear in a region of the spectrum devoid of other carbohydrate peaks or background protein signals. Two N-glycan peaks corresponding to the N45 and N162 N-glycans were dispersed from the rapidly averaged peaks corresponding to the N38, N74, and N169 N-glycans. We used a combination of NMR and 1 μs all-atom computational simulations to identify unexpected contacts between the N45 N-glycan and CD16A polypeptide residues.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Carbohydrate Conformation
  • Carbohydrates / chemistry*
  • Humans
  • Nuclear Magnetic Resonance, Biomolecular / methods*
  • Peptide Fragments / metabolism
  • Polysaccharides / metabolism
  • Protein Conformation
  • Receptors, IgG / chemistry*
  • Receptors, IgG / metabolism*

Substances

  • Carbohydrates
  • FCGR3A protein, human
  • Peptide Fragments
  • Polysaccharides
  • Receptors, IgG