Dynamic Shielding and Allosteric Modulation of Erythropoietin by Glycosylation

Glycosylation is a ubiquitous and essential post-translational modification that regulates protein structure, solubility, and function. Yet, the mechanisms by which glycans modulate the physicochemical properties of protein surfaces remain incompletely understood. Erythropoietin (EPO), a therapeutic glycoprotein with three N-glycosylation sites, provides a tractable model for dissecting site-specific glycan effects on protein functions. Here, we employ glycan-focused enhanced molecular dynamics simulations, specifically generalized replica exchange with solute tempering (gREST) to overcome the limited sampling of conventional MD and capture the extensive conformational heterogeneity of glycans. Our results demonstrate that glycan effects are highly non-additive: specific combinations of glycosylation sites yield emergent structural outcomes through spatial and dynamical cooperativity. Among them, the N83-linked glycan plays a dominant role in shielding a hydrophobic surface helix, thereby reducing local solvent-accessible hydropathy. Strikingly, the extent of this glycan-mediated surface masking quantitatively correlates with experimentally measured retention times in hydrophobic interaction chromatography, establishing a functional link between molecular-scale shielding and macroscopic behavior. These findings reveal that N-glycans modulate protein surfaces not only through local steric occlusion but also via long-range allosteric effects, providing a new framework for understanding and engineering glycoprotein properties.