Solution structure of a variant of human pancreatic secretory trypsin inhibitor determined by nuclear magnetic resonance spectroscopy.

The structure of a variant of human pancreatic secretory trypsin inhibitor (PSTI) has been determined by 1H nuclear magnetic resonance (n.m.r.) spectroscopy and a combination of distance geometry and molecular dynamics simulations. After complete assignment of the 1H signals, the nuclear Overhauser data imply the existence of a rather well-determined tertiary structure stabilized by a central alpha-helix and a short three-stranded beta-sheet. The tertiary structure of the amino terminus and of the loop 11-17 could not be defined by n.m.r. data, suggesting a high flexibility in these areas. As the crystal structures of two complexes of human PSTI variants and that of an uncomplexed variant are also known a comparison of the PSTI tertiary structure in solution and in the crystal is now possible.