Fig. 1: MS analysis of the LAT1-4F2hc complex.

A Structure of LAT1-4F2hc as reported previously (PDB: 6IRT). Four N-glycans at Asn365, Asn 381, Asn424 and Asn506 are highlighted in purple. The covalently linked 4F2hc-Cys164 (blue) and LAT1-Cys210 (green) are shown. Two lipid-like molecules are shown (pink space filled). B Annotation of potential PTM sites, namely phosphorylation, N-glycosylation and disulfide bonds on 4F2hc and LAT1. C Mass spectrum of the LAT1-4F2hc complex from OGNG micelles. The molecular masses of heterodimeric and an unexpected super-dimeric form of the LAT1-4F2hc complexes are calculated as ~140 kDa and ~280 kDa, respectively. D An expansion of the +26 charge state from the native mass spectrum of the heterodimeric LAT1-4F2hc complex. The Δm/z between the adjacent peaks is calculated and plotted as a scatter plot. The averaged Δm/z (2.81) is plotted as a purple line with the shaded area corresponding to one standard deviation (±0.19, light purple). Each fine structure peak differs by ~73 Da. E Illustration of anticipated N-glycan modifications on LAT1-4F2hc complex. N-glycan branching, extension, sialylation and fucosylation are common features found in the glycome of LAT1-4F2hc. F An illustration of how the combinatorial effects of N-glycan branching, extension, sialylation and fucosylation impact the molecular weight (MW) of the intact glycoprotein. Different combinations of these monosaccharide residues result in repeating 72.95 ± 0.69 Da increments on the intact glycoprotein masses (Supplementary Fig. 2). G Zero-charged spectrum of LAT1-4F2hc. The base peak labelled with a red asterisk is assigned as LAT1-4F2hc with one tri-antennary and three tetra-antennary sialylated N-glycans with four or six additional fucose residues. The N-glycan compositions of other peaks can be inferred based on the mass differences to the base peak.