Characterization of the interaction between human plasma fibronectin and collagen by means of affinity electrophoresis

Abstract

The interaction between human plasma fibronectin and different types and forms of collagen were analysed by affinity electrophoresis at different pH values. The fibronectin bound tightly to collagen type I, III and IV, but not to type V. The fibronectin interacted better with the denatured form of collagen type I (gelatin) than with the native form. At pH < 5.5 the fibronectin exhibited much lower affinity to gelatin than at pH > 8.0. The interaction between the fibronectin and gelatin was further analysed by affinity electrophoresis in which apparent dissociation constants ( K d) of the fibronectin for gelatin were calculated, and effects of urea, 2-mercaptoethanol and temperature on the interaction were examined. The fibronectin markedly diminished its affinity to gelatin at 3 M urea to give K d = 2.5 · 10 −6 M, which was 1000 times larger than the value without urea. The fibronectin dissociated into its monomers and the monomers diminished their affinity to gelatin in a stepwise fashion with increase in concentration of 2-mercaptoethanol. The fibronectin diminished the affinity to gelatin by elevating temperature, and van't Hoff plots of log K d values against the reciprocal of absolute temperature ( T) showed that log K d was inversely proportional to 1/ T in the range 15–50°C, and the thermodynamic parameters of the standard enthalpy change, the standard free energy change and the entropy change at 37°C for association of fibronectin and gelatin were all negative. At 60°C the affinity of fibronectin to gelatin was not detectable. These results suggest that a hydrophilic interaction, such as hydrogen bonding or van der Waals interaction, plays an important role in the binding of fibronectin and gelatin, and conformational changes in the fibronectin molecule may occur owing to the stepwise reduction of inter- and intra-chain disulphide bonds or to the heat of denaturation at 60°C.