Solution structure of the kringle 4 domain from human plasminogen by 1H nuclear magnetic resonance spectroscopy and...

Kringle 4 is an autonomous structural and folding domain within the proenzyme plasminogen. Homologous domains are found throughout the blood clotting and fibrinolytic proteins. In this paper, we present the almost complete assignment of the 1H nuclear magnetic resonance (n.m.r.) spectrum of the kringle 4 domain of human plasminogen. A detailed structural analysis has been completed. The sequential pattern of nuclear Overhauser enhancements indicated little regular secondary structure but rather a series of turns and loops connecting beta-strands. A small stretch of antiparallel beta-sheet was identified between the residues 61 to 63 and 71 to 73 and the close proximity of other strands was determined from two-dimensional nuclear Overhauser enhancement spectra. Slowly exchanging amide (NH) resonances were found to be associated with residues of the beta-sheet and neighbouring strands that support the hydrophobic core of the domain. A total of 526 interproton distance constraints and two hydrogen bonds were specified as input to the distance geometry program DISGEO. Tertiary structures were produced that were consistent with the n.m.r. data. The structures were compared with that of our earlier model based on n.m.r. studies and with that of prothrombin fragment 1 determined crystallographically.