Effect of serum albumin on glycosaminoglycan inhibition of hydroxyapatite formation

The interaction of proteins with hydroxyapatite (HAP), specifically proteoglycans and their spatial arms, glycosaminoglycans (GAGs) in addition to serum proteins, play an important role in regulating biological mineralisation. In this study, seeded HAP growth experiments revealed that inhibition of HAP formation by bovine serum albumin (BSA) was significantly elevated in combination with chondroitin 4-sulphate (C4S) versus BSA with heparin. Data suggest that C4S and BSA adsorb to different calcium sites on the HAP surface. In contrast, complexes of heparin and BSA may adsorb to HAP, thus reducing the rate of inhibition due to steric effects. In addition, the amount of protein bound to HAP growth seed was significantly higher in the presence of heparin versus C4S, confirming this suggestion. Furthermore, the data indicate that a GAG-induced conformational change in BSA occurs, which affects inhibition. This work provides novel information concerning binary molecule modulation of HAP growth.