Characterization of a 59 kDa gelatin-binding fragment of buffalo plasma fibronectin

Limited proteolysis of buffalo plasma fibronectin (FN) by thermolysin yielded four gelatin-binding fragments of which, the major 59 kDa fragment, GBF1, was isolated by gelatin-Sepharose and heparin-Sepharose affinity columns. GBF1 appeared during early phase of thermolysin digestion and remained intact even after 4 hr of digestion. GBF1 may be similar to 56 kDa gelatin-binding fragment of FNs from human and hamster plasma. But, it is more resistant to thermolysin cleavage. The fragment binds to heparin with low affinity. On the basis of the structure of human plasma FN, the modular structure of GBF1 may be given as: 6Fn1 1Fn2 2Fn2 7Fn1 8Fn1 9Fn1 1Fn3. Biophysical properties of GBF1 suggest an expanded native conformation. The interaction of the fragment with gelatin is pH-dependent and independent of NaCl concentration.