Impact of Temperature on Heparin and Protein Interactions.

Heparin has many important biological activities, associated with a diverse set of interactions with biologically functional proteins. The binding mechanisms and biological significance of heparin-protein interactions have attracted wide attention. However, the temperature sensitivity of heparin-protein interaction is relatively unstudied. The impact of temperature on the binding of heparin to three representative heparin-binding proteins, antithrombin III (AT III), fibroblast growth factor-1 (FGF1) and fibroblast growth factor-2 (FGF2) are evaluated. The affinity and kinetics of these interactions were measured at 10°C, 25°C and 30°C. The association rate, dissociation rate, binding affinity and binding mass were compared at different temperatures. In the two state binding process between AT III and heparin, temperature played a negligible role on ATIII binding to heparin (1st state reaction), but demonstrated a role in the conformational change process (2nd state reaction). In the case of FGF1 and FGF2, the kinetics and affinity, while distinctly different at the temperatures studies, were still within the same order of magnitude. Based these results, we conclude that it many cases it is possible to perform surface plasmon resonance measurements of heparin-protein interaction at different temperatures, especially at reduced (ambient or lower) temperatures, and obtain comparable binding data.