The mechanism of papain inhibition by peptidyl aldehydes.
نویسندگان
چکیده
Various mechanisms for the reversible formation of a covalent tetrahedral complex (TC) between papain and peptidyl aldehyde inhibitors were simulated by DFT calculations, applying the quantum mechanical/self consistent reaction field (virtual solvent) [QM/SCRF(VS)] approach. Only one mechanism correlates with the experimental kinetic data. The His-Cys catalytic diad is in an N/SH protonation state in the noncovalent papain-aldehyde Michaelis complex. His159 functions as a general base catalyst, abstracting a proton from the Cys25, whereas the activated thiolate synchronously attacks the inhibitor's carbonyl group. The final product of papain inhibition is the protonated neutral form of the hemithioacetal TC(OH), in agreement with experimental data. The predicted activation barrier g enz≠ = 5.2 kcal mol⁻¹ is close to the experimental value of 6.9 kcal mol⁻¹. An interpretation of the experimentally observed slow binding effect for peptidyl aldehyde inhibitors is presented. The calculated g cat≠ is much lower than the rate determining activation barrier of hemithioacetal formation in water, g w≠, in agreement with the concept that the preorganized electrostatic environment in the enzyme active site is the driving force of enzyme catalysis. We have rationalized the origin of the acidic and basic pK(a)'s on the k₂/K(S) versus pH bell-shaped profile of papain inhibition by peptidyl aldehydes.
منابع مشابه
Characterization of the active site of human multicatalytic proteinase.
The activity of multicatalytic proteinase against synthetic substrates and the kinetics of its inhibition by a range of class-specific inhibitors have been investigated. The enzyme was found to have a broader pH activity profile than previously noted, being active against succinyl-Ala-Ala-Phe-7-amino-4-methylcoumarin optimally at pH 4.5 and against benzyloxycarbonyl-Gly-Gly-Arg-7-amino-4-methyl...
متن کاملThe activation of papain and the inhibition of the active enzyme by carbonyl reagents.
The activation of papain with four different activators is not accompanied by the binding of any of them to the protein. These experiments, taken together with previously reported results, show that the inactive form of papain prepared by the method of Kimmel and Smith (J. Biol. Chem., 207, 5’75 (1954)) is a mixed disulfide formed between the active site sulfhydryl group of the protein and free...
متن کاملInhibition of the proteolytic activity of the multicatalytic proteinase complex (proteasome) by substrate-related peptidyl aldehydes.
Evidence indicates that a component of the multicatalytic proteinase complex (MPC) that preferentially cleaves bonds after branched chain amino acids (BrAAP) is a major factor responsible for the protein-degrading activity of the MPC. We report here the synthesis of substrate-related peptidyl aldehydes that inhibit the activity of this component toward both synthetic peptide substrates and prot...
متن کاملInhibition of chickpea seedling copper amine oxidases by tetraethylenepentamine
Copper amine oxidases are important enzymes, which contribute to the regulation of mono- and polyamine levels. Each monomer contains one Cu(II) ion and 2,4,5-trihydroxyphenylalanine (TPQ) as cofactors. They catalyze the oxidative deamination of primary amines to aldehydes with a ping-pong mechanism consisting of a transamination. The mechanism is followed by the transfer of two electrons to mol...
متن کاملذخیره در منابع من
با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید
برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید
ثبت ناماگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید
ورودعنوان ژورنال:
- Proteins
دوره 79 3 شماره
صفحات -
تاریخ انتشار 2011