Binding of bovine basic pancreatic trypsin inhibitor (Kunitz) as well as bovine and porcine pancreatic secretory trypsin inhibitor (Kazal) to human cathepsin G: a kinetic and thermodynamic study.
The effect of pH and temperature on kinetic and thermodynamic parameters for the binding of the bovine basic pancreatic trypsin inhibitor (Kunitz inhibitor; BPTI) as well as bovine and porcine pancreatic secretory trypsin inhibitor (Kazal inhibitor; bovine and porcine PSTI, respectively) to human cathepsin G (EC 3.4.21.20) has been investigated. The affinity of the macromolecular inhibitors examined for cathepsin G is characterized by an endothermic, entropy-driven, behaviour, and shows the following trend: BPTI > bovine PSTI > porcine PSTI. The affinity difference of BPTI as well as of bovine and porcine PSTI for cathepsin G is mostly accounted for by changes in the values of the apparent dissociation rate constant for the proteinase:inhibitor complex destabilization. On increasing the pH from 4.5 to 9.5 (at 25.0 degrees C), the affinity of BPTI, as well as bovine and porcine PSTI for cathepsin G increases thus reflecting the acidic-pK shift of the His-57 catalytic residue from approximately 6.9 in the free enzyme to approximately 5.0 in the serine proteinase:inhibitor complexes. The BPTI as well as the bovine and porcine PSTI binding properties of cathepsin G have been analyzed in parallel with those of related serine (pro)enzyme/macromolecular inhibitor systems. Considering the known molecular models, the observed binding behaviour of BPTI as well as that of bovine and porcine PSTI to cathepsin G has been related to the inferred stereochemistry of the serine proteinase/inhibitor contact region(s).
Fioretti
E
E
Department of Molecular, Cellular and Animal Biology, University of Camerino, MC, Italy.
Angeletti
M
M
Coletta
M
M
Ascenzi
P
P
Bolognesi
M
M
Menegatti
E
E
Rizzi
M
M
Ascoli
F
F
D000818:Animals; D007611:Aprotinin / Q000378:metabolism*; D056649:Cathepsin G; D002403:Cathepsins / Q000378:metabolism*; D002417:Cattle; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D012697:Serine Endopeptidases; D013552:Swine; D013816:Thermodynamics; D014359:Trypsin Inhibitor, Kazal Pancreatic / Q000378:metabolism*
D014359:Trypsin Inhibitor, Kazal Pancreatic; D007611:Aprotinin; D002403:Cathepsins; D012697:Serine Endopeptidases; C534094:CTSG protein, human; D056649:Cathepsin G