Influence of Glycosaminoglycan Binding/Non-Binding Interactions on Bone Morphogenetic Protein-2 Unfolding Dynamics and Activity: Mechanistic Insights and Implications

Glycosaminoglycans (GAGs), a class of carbohydrates integral to the extracellular matrix in biological systems, such as the connective tissue, cornea, and synovial fluid, significantly influence protein dynamics. This study investigates the unfolding kinetics and dynamics of Bone Morphogenetic Protein-2 (BMP-2) in the presence of glycosaminoglycans, specifically, hyaluronic acid (HA) and sulfated hyaluronic acid (SHA). The findings reveal that BMP-2 undergoes faster unfolding in the presence of SHA compared with HA in chemical denaturation. This accelerated unfolding can be attributed to a complex interplay between viscosity and the binding or nonbinding interactions between the glycosaminoglycans and the protein. Despite HA exhibiting a higher viscosity than SHA, the anisotropy of the intrinsic fluorophore of the protein demonstrates a significantly higher fluorescence anisotropy and anisotropy decay time in the SHA environment. Fluorescence lifetime measurements and rotational correlation times further substantiate this observation, with anisotropy kinetics indicating a binding interaction of BMP-2 with SHA. Additionally, the protein's unfolding mechanism in the presence of HA and SHA follows a mixed pathway, involving both direct and indirect processes. Energetically, the unfolding of BMP-2 in the SHA environment is considerably more stable than that in HA, suggesting a more robust interaction between the protein and sulfated glycosaminoglycans.