Three-Dimensional structure of the complexes between bovine chymotrypsinogen a and two recombinant variants of human pancreatic secretory trypsin inhibitor (kazal-Type).
Variants of the human pancreatic secretory trypsin inhibitor (PSTI) have been
created during a protein design project to generate a high-affinity inhibitor
with respect to some serine proteases other than trypsin. Two modified versions
of human PSTI with high affinity for chymotrypsin were crystallized as a complex
with chymotrypsinogen. Both crystallize isomorphously in space group P4(1)2(1)2
with lattice constants a = 84.4 A, c = 86.7 A and diffract to 2.3 A resolution.
The structure was solved by molecular replacement. The final R-value after
refinement with 8.0 to 2.3 A resolution data was 19.5% for both complexes after
inclusion of about 50 bound water molecules. The overall three-dimensional
structure of PSTI is similar to the structure of porcine PSTI in the trypsinogen
complex (1TGS). Small differences in the relative orientation of the binding
loop and the core of the inhibitors indicate flexible adaptation to the
proteases. The chymotrypsinogen part of the complex is similar to chymotrypsin.
After refolding induced by binding of the inhibitor the root-mean-square
difference of the active site residues A186 to A195 and A217 to A222 compared to
chymotrypsin was 0.26 A.
