Binding to thermolysin of phenolate-containing inhibitors necessitates a revised mechanism of catalysis.
نویسندگان
چکیده
Competitive inhibition as a function of pH for the metalloendoprotease thermolysin by derivatives of L-alpha-(2-hydroxyphenyl)benzenepropanoyl-L- tryptophanylglycylglycine exhibits a diagnostic bell shape. Binding is maximal between two pKa values: on the acidic limb the apparent Ki value is regulated by an unchanging enzymic ionization (pKa 5.3) which is also seen in the substrate-hydrolysis kinetics (kcat/Km), whereas the alkaline limb for inhibition varies and depends specifically on the pKa of the phenolic group in the inhibitor. Although it should be the phenolate form of the inhibitor that co-ordinates more efficiently to the active-site Zn2+, the apparent Ki shifts from pH-independent at pH values immediately below the inhibitor's pKa to progressively weaker binding at higher pH. This is explained by an anomalous acidity for the exchangeable solvent molecule that is attached to enzymic Zn2+ in the absence of substrate or inhibitor. Since OH- cannot be displaced from the enzyme as readily as H2O, a compensating pKa of 5.3 possessed by Zn(2+)-bound water rationalizes the binding characteristics, yielding the level pH profile exhibited at intermediate pH values. Recognition of the implicit heightened Lewis acidity of the metal ion in thermolysin leads to a revision of the mechanism of catalysis. The substrate amide bond becomes activated for hydrolysis by carbonyl-group co-ordination to the especially acidic Zn2+ ion (completely displacing the H2O/OH- species otherwise bound). The imidazole group of enzymic residue His-231, also discerned in the pH profile for kcat/Km from its pKa of 8, provides general-base assistance for hydration of the activated scissile linkage in the first committed step of catalysis. Additional evidence from inhibition patterns shows how substrate-binding energy may be employed in this scheme to promote hydrolysis of peptides by thermolysin.
منابع مشابه
Binding of hydroxamic acid inhibitors to crystalline thermolysin suggests a pentacoordinate zinc intermediate in catalysis.
متن کامل
Regioselectivity in acylation of oligosaccharides catalyzed by the metalloprotease thermolysin
Investigation of the acylation scope of carbohydrates by metalloprotease thermolysin immobilized on Celite as biocatalyst has been carried out. The reactions were performed in DMSO, a good solvent for carbohydrates, where the enzyme has previously shown its activity in transesterifications of sucrose, maltose and maltose-containing oligosaccharides. Surprisingly, no reaction was observed for gl...
متن کاملSlow- and fast-binding inhibitors of thermolysin display different modes of binding: crystallographic analysis of extended phosphonamidate transition-state analogues.
The modes of binding to thermolysin of two phosphonamidate peptide inhibitors, carbobenzoxy-GlyP-L-Leu-L-Leu (ZGPLL) and carbobenzoxy-L-PheP-L-Leu-L-Ala (ZFPLA), have been determined by X-ray crystallography and refined at high resolution to crystallographic R-values of 17.7% and 17.0%, respectively. (GlyP is used to indicate that the trigonal carbon of the peptide linkage is replaced by the te...
متن کاملInvestigation the Mechanism of Interaction between Inhibitor ALISERTIB with Protein Kinase A and B Using Modeling, Docking and Molecular Dynamics Simulation
The high level of conservation in ATP-binding sites of protein kinases increasingly demandsthe quest to find selective inhibitors with little cross reactivity. Kinase kinases are a recently discovered group of Kinases found to be involved in several mitotic events. These proteins represent attractive targets for cancer therapy with several small molecule inhibitors undergoing different ph...
متن کاملResistance mechanism of human immunodeficiency virus type-1 protease to inhibitors: A molecular dynamic approach
Human immunodeficiency virus type 1 (HIV-1) protease inhibitors comprise an important class of drugs used in HIV treatments. However, mutations of protease genes accelerated by low fidelity of reverse transcriptase yield drug resistant mutants of reduced affinities for the inhibitors. This problem is considered to be a serious barrier against HIV treatment for the foreseeable future. In this st...
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:
- The Biochemical journal
دوره 302 ( Pt 1) شماره
صفحات -
تاریخ انتشار 1994