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Iqbal A, Clifton IJ, Bagonis M, Kershaw NJ, Domene C, Claridge TDW, Wharton CW, Schofield CJ. Anatomy of a Simple Acyl Intermediate in Enzyme Catalysis: Combined Biophysical and Modeling Studies on Ornithine Acetyl Transferase. J Am Chem Soc 2008; 131:749-57. [DOI: 10.1021/ja807215u] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Aman Iqbal
- Chemistry Research Laboratory, University of Oxford, 12 Mansfield Road, Oxford, OX1 3TA, U.K., Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, Oxford, OX1 3QZ, U.K., School of Biosciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, U.K
| | - Ian J. Clifton
- Chemistry Research Laboratory, University of Oxford, 12 Mansfield Road, Oxford, OX1 3TA, U.K., Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, Oxford, OX1 3QZ, U.K., School of Biosciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, U.K
| | - Maria Bagonis
- Chemistry Research Laboratory, University of Oxford, 12 Mansfield Road, Oxford, OX1 3TA, U.K., Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, Oxford, OX1 3QZ, U.K., School of Biosciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, U.K
| | - Nadia J. Kershaw
- Chemistry Research Laboratory, University of Oxford, 12 Mansfield Road, Oxford, OX1 3TA, U.K., Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, Oxford, OX1 3QZ, U.K., School of Biosciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, U.K
| | - Carmen Domene
- Chemistry Research Laboratory, University of Oxford, 12 Mansfield Road, Oxford, OX1 3TA, U.K., Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, Oxford, OX1 3QZ, U.K., School of Biosciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, U.K
| | - Timothy D. W. Claridge
- Chemistry Research Laboratory, University of Oxford, 12 Mansfield Road, Oxford, OX1 3TA, U.K., Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, Oxford, OX1 3QZ, U.K., School of Biosciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, U.K
| | - Christopher W. Wharton
- Chemistry Research Laboratory, University of Oxford, 12 Mansfield Road, Oxford, OX1 3TA, U.K., Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, Oxford, OX1 3QZ, U.K., School of Biosciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, U.K
| | - Christopher J. Schofield
- Chemistry Research Laboratory, University of Oxford, 12 Mansfield Road, Oxford, OX1 3TA, U.K., Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, Oxford, OX1 3QZ, U.K., School of Biosciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, U.K
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Topf M, Várnai P, Schofield CJ, Richards WG. Molecular dynamics simulations of the acyl-enzyme and the tetrahedral intermediate in the deacylation step of serine proteases. Proteins 2002; 47:357-69. [PMID: 11948789 DOI: 10.1002/prot.10097] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Despite the availability of many experimental data and some modeling studies, questions remain as to the precise mechanism of the serine proteases. Here we report molecular dynamics simulations on the acyl-enzyme complex and the tetrahedral intermediate during the deacylation step in elastase catalyzed hydrolysis of a simple peptide. The models are based on recent crystallographic data for an acyl-enzyme intermediate at pH 5 and a time-resolved study on the deacylation step. Simulations were carried out on the acyl enzyme complex with His-57 in protonated (as for the pH 5 crystallographic work) and deprotonated forms. In both cases, a water molecule that could provide the nucleophilic hydroxide ion to attack the ester carbonyl was located between the imidazole ring of His-57 and the carbonyl carbon, close to the hydrolytic position assigned in the crystal structure. In the "neutral pH" simulations of the acyl-enzyme complex, the hydrolytic water oxygen was hydrogen bonded to the imidazole ring and the side chain of Arg-61. Alternative stable locations for water in the active site were also observed. Movement of the His-57 side-chain from that observed in the crystal structure allowed more solvent waters to enter the active site, suggesting that an alternative hydrolytic process directly involving two water molecules may be possible. At the acyl-enzyme stage, the ester carbonyl was found to flip easily in and out of the oxyanion hole. In contrast, simulations on the tetrahedral intermediate showed no significant movement of His-57 and the ester carbonyl was constantly located in the oxyanion hole. A comparison between the simulated tetrahedral intermediate and a time-resolved crystallographic structure assigned as predominantly reflecting the tetrahedral intermediate suggests that the experimental structure may not precisely represent an optimal arrangement for catalysis in solution. Movement of loop residues 216-223 and P3 residue, seen both in the tetrahedral simulation and the experimental analysis, could be related to product release. Furthermore, an analysis of the geometric data obtained from the simulations and the pH 5 crystal structure of the acyl-enzyme suggests that since His-57 is protonated, in some aspects, this crystal structure resembles the tetrahedral intermediate.
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Affiliation(s)
- Maya Topf
- Physical and Theoretical Chemistry Laboratory, University of Oxford, Oxford, United Kingdom.
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