Saxs Data Based Glycosylated Models of Human Alpha-1-Acid Glycorprotein, a Key Player in Health, Disease and Drug Circulation

Abstract

Plasma Alpha-1-glycoprotein (AGP) binds diverse drugs, its isoforms and their levels vary significantly in acute phases of health. Relative binding of drugs to AGP and albumin has been used to model their release profiles, structural insights on glycosylated form of AGP will certainly improve estimations. Main challenges are: 1) heavy glycosylation of AGP (~50% of its mass), 2) isoforms of primary structure co-exist, and 3) extreme heterogeneity in the glycan motifs have been reported. Our small angle X-ray scattering (SAXS) data on plasma extracted AGP showed interparticulate effect from 283-313 K which disappeared irreversibly upon further heating to 343K. Using ALPHAFOLD2 server, the protein only portion could be modelled but its theoretical SAXS profile did not match acquired experimental data. Using mass spectra-based information, we attached glycan motifs at different known sites to compute four models of fully glycosylated AGP. Importantly, calculated SAXS profiles of our glycosylated models agreed well with the experimental data. Docking runs revealed that in silico interaction of different drugs when varied using unglycosylated vs. glycosylated model as receptor. Finally, we propose that our SAXS based models of glycoprotein are better representation of the molecule and should be considered for structure-based analysis and/or estimations.