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QM/MM simulations identify the determinants of catalytic activity differences between type II dehydroquinase enzymes.

ABSTRACT: Type II dehydroquinase enzymes (DHQ2), recognized targets for antibiotic drug discovery, show significantly different activities dependent on the species: DHQ2 from Mycobacterium tuberculosis (MtDHQ2) and Helicobacter pylori (HpDHQ2) show a 50-fold difference in catalytic efficiency. Revealing the determinants of this activity difference is important for our understanding of biological catalysis and further offers the potential to contribute to tailoring specificity in drug design. Molecular dynamics simulations using a quantum mechanics/molecular mechanics potential, with correlated ab initio single point corrections, identify and quantify the subtle determinants of the experimentally observed difference in efficiency. The rate-determining step involves the formation of an enolate intermediate: more efficient stabilization of the enolate and transition state of the key step in MtDHQ2, mainly by the essential residues Tyr24 and Arg19, makes it more efficient than HpDHQ2. Further, a water molecule, which is absent in MtDHQ2 but involved in generation of the catalytic Tyr22 tyrosinate in HpDHQ2, was found to destabilize both the transition state and the enolate intermediate. The quantification of the contribution of key residues and water molecules in the rate-determining step of the mechanism also leads to improved understanding of higher potencies and specificity of known inhibitors, which should aid ongoing inhibitor design.

SUBMITTER: Lence E

PROVIDER: S-EPMC6011038 | biostudies-literature | 2018 Jun

REPOSITORIES: biostudies-literature

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QM/MM simulations identify the determinants of catalytic activity differences between type II dehydroquinase enzymes.

Lence Emilio E van der Kamp Marc W MW González-Bello Concepción C Mulholland Adrian J AJ

Organic & biomolecular chemistry 20180601 24

Type II dehydroquinase enzymes (DHQ2), recognized targets for antibiotic drug discovery, show significantly different activities dependent on the species: DHQ2 from Mycobacterium tuberculosis (MtDHQ2) and Helicobacter pylori (HpDHQ2) show a 50-fold difference in catalytic efficiency. Revealing the determinants of this activity difference is important for our understanding of biological catalysis and further offers the potential to contribute to tailoring specificity in drug design. Molecular dyn ...[more]

PMID: 29767194

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Project description:Human arginase I (HARGI) is a metalloprotein highly expressed in the liver cytosol and catalyzes the hydrolysis of l-arginine to form l-ornithine and urea. Understanding the reaction mechanism would be highly helpful to design new inhibitor molecules for HARGI as it is a target for heart- and blood-related diseases. In this study, we explored the hydrolysis reaction mechanism of HARGI with antiferromagnetic and ferromagnetic coupling between two Mn(II) ions at the catalytic site by employing molecular dynamics simulations coupled with quantum mechanics and molecular mechanics (QM/MM). The spin states, high-spin ferromagnetic couple (S Mn1 = 5/2, S Mn2 = 5/2), low-spin ferromagnetic couple (S Mn1 = 1/2, S Mn2 = 1/2), high-spin antiferromagnetic couple (S Mn1 = 5/2, S Mn2 = -5/2), and low-spin antiferromagnetic couple (S Mn1 = 1/2, S Mn2 = -1/2) are considered, and the calculated energetics for the complex of the substrate and HARGI are compared. The results show that the high-spin antiferromagnetic couple (S Mn1 = 5/2, S Mn2 = -5/2) is more stable than other spin states. The low-spin ferromagnetic and antiferromagnetic coupled states are highly unstable compared with the corresponding high-spin states. The high-spin antiferromagnetic couple (S Mn1 = 5/2, S Mn2 = -5/2) is stabilized by 0.39 kcal/mol compared with the ferromagnetic couple (S Mn1 = 5/2, S Mn2 = 5/2). The reaction mechanism is independent of spin states; however, the energetics of transition states and intermediates are more stable in the case of the high-spin antiferromagnetic couple (S Mn1 = 5/2, S Mn2 = -5/2) than the corresponding ferromagnetic state. It is evident that the calculated coupling constants are higher for antiferromagnetic states and, interestingly, superexchange coupling is found to occur between Mn(II) ions via hydroxide ions in a reactant. The hydroxide ion enhances the coupling interaction and initiates the catalytic reaction. It is also noted that the first intermediate structure where there is no superexchange coupling is similar to the known inhibitor 2(S)-amino-6-boronohexanoic acid.

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QM/MM simulations identify the determinants of catalytic activity differences between type II dehydroquinase enzymes.

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QM/MM simulations identify the determinants of catalytic activity differences between type II dehydroquinase enzymes.

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