Specific interactions between cryogel components: Role of extra domain A containing fibronectin in cryogelation

Cryogel is a physical gel formed by heterophilic aggregation of extra domain A containing fibronectin [EDA(+)FN], plasma fibronectin (pFN), fibrinogen (Fbg) and heparin (Hep), which are found in high concentrations in the blood of patients suffering from rheumatoid arthritis. In this study, we clarify the specific interactions between cryogel components in terms of the affinity constant (K_A), obtained by surface plasmon resonance (SPR). It is found that Fbg self-interactions occur at lower temperatures, and that K_A of Fbg-Hep changes with temperature. Specifically, K_A (2.0×10⁸ [M^-1]) of Fbg-Hep at 5°C increases significantly from that (1.0×10⁷ [M^-1]) at 40°C. K_A of EDA(+)FN-Hep increases with temperature, by approximately 100-fold between 40°C (K_A=10¹² [M^-1]) and 20°C (K_A=10¹⁰ [M^-1]). Although K_A of the FN fragments of Hep-binding domain containing an EDA region [EDA(+)HBD(+)] and Hep increases with temperatures above 30°C, K_As of HBD(+)-Hep and EDA(+)-Hep are not temperature-dependent. Therefore, EDA(+)HBD(+), formed as a special structure for high Hep affinity, exhibits temperature-dependent interaction with Hep. These results suggest that the main role of EDA(+)FN in cryogelation is to support the interaction with Hep.