Thermodynamic modeling of internal equilibria involved in the activation of trypsinogen.
The effect of activating dipeptides, sequentially homologous to the Ile16-Val17N-terminus of bovine beta-trypsin (beta-trypsin), on equilibria involved in the binding of strong ligands (i.e., n-butylamine, the bovine basic pancreatic trypsin inhibitor (Kunitz-type inhibitor; BPTI) and the porcine pancreatic secretory trypsin inhibitor (Kazal-type inhibitor, type I; PSTI)) to bovine trypsinogen (trypsinogen) was investigated at pH 5.51 (I = 0.1 M) and T = 21.0 +/- 0.5 degrees C; under the same experimental conditions, thermodynamics for the binding of strong ligands to beta-trypsin was also obtained. The equilibria involved in the binding of activating dipeptides and/or inhibitors to beta-trypsin and to its zymogen are described according to an induced-fit formalism, taking into account ligand-linked interaction(s) between different functional and structural domains of the (pro)enzyme possibly involved in the trypsinogen-to-beta-trypsin activation pathway. The analysis of data is focussed on parameters describing interactions between the so-called Ile-Val pocket (where the Ile16-Val17 N-terminus of beta-trypsin or activating dipeptides bind) and the primary and/or secondary recognition subsite(s) (where strong ligands associate) present in the (pro)enzyme. Such an analysis allows to dissect the contributions due to the primary recognition subsite, where small mono-functional ligands (e.g., n-butylamine) bind, from those of the secondary subsite(s), which are additional recognition clefts for macromolecular inhibitors (e.g., BPTI and PSTI).
Coletta
M
M
Department of Biochemical Sciences, University of Rome La Sapienza, Italy.
Ascenzi
P
P
Bravin
L
L
Amiconi
G
G
Bolognesi
M
M
Guarneri
M
M
Menegatti
E
E
D001665:Binding Sites / Q000502:physiology; D002082:Butylamines / Q000378:metabolism; D004151:Dipeptides / Q000378:metabolism; D004789:Enzyme Activation; D007700:Kinetics; D008956:Models, Chemical; D008958:Models, Molecular; D013379:Substrate Specificity; D013816:Thermodynamics; D014359:Trypsin Inhibitor, Kazal Pancreatic / Q000378:metabolism; D014360:Trypsin Inhibitor, Kunitz Soybean / Q000378:metabolism; D014362:Trypsinogen / Q000378:metabolism*
D002082:Butylamines; D004151:Dipeptides; D014359:Trypsin Inhibitor, Kazal Pancreatic; D014362:Trypsinogen; D014360:Trypsin Inhibitor, Kunitz Soybean; C032462:n-butylamine