THE SOLUTION STRUCTURE AND BACKBONE DYNAMICS OF THE FIBRONECTIN TYPE-I AND EPIDERMAL GROWTH FACTOR-LIKE PAIR OF MODULES OF TISSUE-TYPE PLASMINOGEN-ACTIVATOR

Background: The thrombolytic serine protease tissue-type plasminogen activator (t-PA) is a classical modular protein consisting of three types of domain in addition to the serine protease domain: F1 (homologous to fibronectin type I); G (epidermal growth factor-like) and kringle. Biochemical data suggest that the F1 and G modules play a major role in the binding of t-PA to fibrin and to receptors on hepatocytes. Results: We have derived the solution structure of the F1 and G pair of modules from t-PA by two- and three-dimensional NMR techniques, in combination with dynamical simulated annealing calculations. We have also obtained information about the molecule's backbone dynamics through measurement of amide N-15 relaxation parameters. Conclusions: Although the F1 and G modules each adopt their expected tertiary structure, the modules interact intimately to bury a hydrophobic core, and the inter-module linker makes up the third strand of the G module's major beta-sheet. The, new structural results allow the interpretation of earlier mutational data relevant to fibrin-binding and hepatocyte-receptor binding.