Moderate‐Affinity Affibodies Modulate the Delivery and Bioactivity of Bone Morphogenetic Protein‐2

Abstract

AbstractUncontrolled bone morphogenetic protein‐2 (BMP‐2) release can lead to off‐target bone growth and other adverse events. To tackle this challenge, yeast surface display is used to identify unique BMP‐2‐specific protein binders known as affibodies that bind to BMP‐2 with different affinities. Biolayer interferometry reveals an equilibrium dissociation constant of 10.7 nm for the interaction between BMP‐2 and high‐affinity affibody and 34.8 nm for the interaction between BMP‐2 and the low‐affinity affibody. The low‐affinity affibody‐BMP‐2 interaction also exhibits an off‐rate constant that is an order of magnitude higher. Computational modeling of affibody‐BMP‐2 binding predicts that the high‐ and low‐affinity affibodies bind to two distinct sites on BMP‐2 that function as different cell‐receptor binding sites. BMP‐2 binding to affibodies reduces expression of the osteogenic marker alkaline phosphatase (ALP) in C2C12 myoblasts. Affibody‐conjugated polyethylene glycol‐maleimide hydrogels increase uptake of BMP‐2 compared to affibody‐free hydrogels, and high‐affinity hydrogels exhibit lower BMP‐2 release into serum compared to low‐affinity hydrogels and affibody‐free hydrogels over four weeks. Loading BMP‐2 into affibody‐conjugated hydrogels prolongs ALP activity of C2C12 myoblasts compared to soluble BMP‐2. This work demonstrates that affibodies with different affinities can modulate BMP‐2 delivery and activity, creating a promising approach for controlling BMP‐2 delivery in clinical applications.