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Higher Flexibility ...
Higher Flexibility of Glu-172 Explains the Unusual Stereospecificity of Glyoxalase i
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- Jafari, Sonia (author)
- University of Kurdistan
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- Kazemi, Nadia (author)
- University of Kurdistan
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- Ryde, Ulf (author)
- Lund University,Lunds universitet,Beräkningskemi,Enheten för fysikalisk och teoretisk kemi,Kemiska institutionen,Institutioner vid LTH,Lunds Tekniska Högskola,Computational Chemistry,Physical and theoretical chemistry,Department of Chemistry,Departments at LTH,Faculty of Engineering, LTH
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- Irani, Mehdi (author)
- University of Kurdistan
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(creator_code:org_t)
- 2018-04-10
- 2018
- English 15 s.
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In: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 57:9, s. 4944-4958
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Abstract
Subject headings
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- Despite many studies during the latest two decades, the reason for the unusual stereospecificity of glyoxalase I (GlxI) is still unknown. This metalloenzyme converts both enantiomers of its natural substrate to only one enantiomer of its product. In addition, GlxI catalyzes reactions involving some substrate and product analogues with a stereospecificity similar to that of its natural substrate reaction. For example, the enzyme exchanges the pro-S, but not the pro-R, hydroxymethyl proton of glutathiohydroxyacetone (HOC-SG) with a deuterium from D2O. To find some clues to the unusual stereospecificity of GlxI, we have studied the stereospecific proton exchange of the hydroxymethyl proton of HOC-SG by this enzyme. We employed density functional theory and molecular dynamics (MD) simulations to study the proton exchange mechanism and origin of the stereospecificity. The results show that a rigid cluster model with the same flexibility for the two active-site glutamate residues cannot explain the unusual stereospecificity of GlxI. However, using a cluster model with full flexibility of Glu-172 or a larger model with the entire glutamates, extending the backbone into the neighboring residues, the results showed that there is no way for HOC-SG to exchange its protons if the alcoholic proton is directed toward Glu-99. However, if the hydroxymethyl proton instead is directed toward the more flexible Glu-172, we find a catalytic reaction mechanism for the exchange of the HS proton by a deuterium, in accordance with experimental findings. Thus, our results indicate that the special stereospecificity of GlxI is caused by the more flexible environment of Glu-172 in comparison to that of Glu-99. This higher flexibility of Glu-172 is also confirmed by MD simulations. We propose a reaction mechanism for the stereospecific proton exchange of the hydroxymethyl proton of HOC-SG by GlxI with an overall energy barrier of 15 kcal/mol.
Subject headings
- NATURVETENSKAP -- Kemi -- Oorganisk kemi (hsv//swe)
- NATURAL SCIENCES -- Chemical Sciences -- Inorganic Chemistry (hsv//eng)
Publication and Content Type
- art (subject category)
- ref (subject category)
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