Sulfation of Hyaluronic Acid Reconfigures the Mechanistic Pathway of Bone Morphogenetic Protein-2 Aggregation

Abstract

Bone morphogenetic protein-2 (BMP-2) is a critical growth factor of bone extracellular matrix (ECM), pivotal for osteogenesis. Glycosaminoglycans, another vital ECM biomolecules, interact with growth factors, affecting signal transduction. Our study focused on hyaluronic acid (HA), a prevalent GAG, and its sulfated derivative (SHA). We explored their impact on BMP-2's conformation, aggregation, and mechanistic aggregation pathways using diverse optical and rheological methods. In the presence of HA and SHA, the secondary structure of BMP-2 underwent a structured transformation, characterized by a substantial increase in beta-sheet content, and a detrimental alteration, manifesting as a shift towards unstructured content, respectively. Although both HA and SHA induced BMP-2 aggregation, their mechanisms differed. SHA led to rapid amorphous aggregates, while HA promoted amyloid fibrils with a lag phase and sigmoidal kinetics. Aggregate size and shape varied; HA produced larger structures, SHA smaller. Each aggregation type followed distinct pathways influenced by viscosity and excluded volume. Higher viscosity, low diffusivity of protein, and higher excluded volume In the presence of HA promote fibrillation having a size in the micrometer range. Low viscosity, high diffusivity of protein, and lesser excluded volume lead to an amorphous size aggregate in the nanometer range