SOLUTION STRUCTURE OF THE AMINO-TERMINAL FRAGMENT OF UROKINASE-TYPE PLASMINOGEN-ACTIVATOR

The amino-terminal fragment (ATF) of urokinase-type plasminogen activa tor is a two domain protein which consists of a growth factor and a kr ingle domain. The H-1, C-13, and N-15 chemical shifts of this protein have been assigned using heteronuclear two- and three-dimensional NMR experiments on selective and uniformly N-15- and N-15/C-13-labeled pro tein isolated from mammalian cells that overexpress the protein. The c hemical shift assignments were used to interpret the NOE data which re sulted in a total of 1299 NOE restraints. The NOE restraints were used along with 27 phi angle restraints and 21 hydrogen-bonding restraints to produce 15 low energy structures. The individual domains in the st ructures are highly converged, but the two domains are structurally in dependent. The root mean square deviations (rmsd) between residues 11- 46 in the growth factor domain and the mean atomic coordinates were 0. 99 +/- 0.2 for backbone heavy atoms and 1.65 +/- 0.2 for all non-hydro gen atoms. For residues 55-130 in the kringle domain, the rmsd was 0.8 4 +/- 0.2 for backbone heavy atoms and 1.42 +/- 0.2 for all non-hydrog en atoms. The overall structures of the individual domains are very si milar to the structures of homologous proteins. However, important str uctural differences between the growth factor and other homologous pro teins were observed in the region which has been implicated in binding the urokinase receptor which may explain, in part, why other growth f actors show no appreciable affinity for the urokinase receptor.