An enzymatic atavist revealed in dual pathways for water activation.
Inosine monophosphate dehydrogenase (IMPDH) catalyzes an essential step in the biosynthesis of guanine nucleotides. This reaction involves two different chemical transformations, an NAD-linked redox reaction and a hydrolase reaction, that utilize mutually exclusive protein conformations with distinc...
| Main Authors: | , , , , , , , , |
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| Format: | Article |
| Language: | English |
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Public Library of Science (PLoS)
2008-08-01
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| Series: | PLoS Biology |
| Online Access: | https://www.ncbi.nlm.nih.gov/pmc/articles/pmid/18752347/pdf/?tool=EBI |
| _version_ | 1819036691860553728 |
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| author | Donghong Min Helen R Josephine Hongzhi Li Clemens Lakner Iain S MacPherson Gavin J P Naylor David Swofford Lizbeth Hedstrom Wei Yang |
| author_facet | Donghong Min Helen R Josephine Hongzhi Li Clemens Lakner Iain S MacPherson Gavin J P Naylor David Swofford Lizbeth Hedstrom Wei Yang |
| author_sort | Donghong Min |
| collection | DOAJ |
| description | Inosine monophosphate dehydrogenase (IMPDH) catalyzes an essential step in the biosynthesis of guanine nucleotides. This reaction involves two different chemical transformations, an NAD-linked redox reaction and a hydrolase reaction, that utilize mutually exclusive protein conformations with distinct catalytic residues. How did Nature construct such a complicated catalyst? Here we employ a "Wang-Landau" metadynamics algorithm in hybrid quantum mechanical/molecular mechanical (QM/MM) simulations to investigate the mechanism of the hydrolase reaction. These simulations show that the lowest energy pathway utilizes Arg418 as the base that activates water, in remarkable agreement with previous experiments. Surprisingly, the simulations also reveal a second pathway for water activation involving a proton relay from Thr321 to Glu431. The energy barrier for the Thr321 pathway is similar to the barrier observed experimentally when Arg418 is removed by mutation. The Thr321 pathway dominates at low pH when Arg418 is protonated, which predicts that the substitution of Glu431 with Gln will shift the pH-rate profile to the right. This prediction is confirmed in subsequent experiments. Phylogenetic analysis suggests that the Thr321 pathway was present in the ancestral enzyme, but was lost when the eukaryotic lineage diverged. We propose that the primordial IMPDH utilized the Thr321 pathway exclusively, and that this mechanism became obsolete when the more sophisticated catalytic machinery of the Arg418 pathway was installed. Thus, our simulations provide an unanticipated window into the evolution of a complex enzyme. |
| first_indexed | 2024-12-21T08:09:33Z |
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| institution | Directory Open Access Journal |
| issn | 1544-9173 1545-7885 |
| language | English |
| last_indexed | 2024-12-21T08:09:33Z |
| publishDate | 2008-08-01 |
| publisher | Public Library of Science (PLoS) |
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| series | PLoS Biology |
| spelling | doaj.art-ddb9bd56b4474bdcb042295fdd6460ad2022-12-21T19:10:42ZengPublic Library of Science (PLoS)PLoS Biology1544-91731545-78852008-08-0168e20610.1371/journal.pbio.0060206An enzymatic atavist revealed in dual pathways for water activation.Donghong MinHelen R JosephineHongzhi LiClemens LaknerIain S MacPhersonGavin J P NaylorDavid SwoffordLizbeth HedstromWei YangInosine monophosphate dehydrogenase (IMPDH) catalyzes an essential step in the biosynthesis of guanine nucleotides. This reaction involves two different chemical transformations, an NAD-linked redox reaction and a hydrolase reaction, that utilize mutually exclusive protein conformations with distinct catalytic residues. How did Nature construct such a complicated catalyst? Here we employ a "Wang-Landau" metadynamics algorithm in hybrid quantum mechanical/molecular mechanical (QM/MM) simulations to investigate the mechanism of the hydrolase reaction. These simulations show that the lowest energy pathway utilizes Arg418 as the base that activates water, in remarkable agreement with previous experiments. Surprisingly, the simulations also reveal a second pathway for water activation involving a proton relay from Thr321 to Glu431. The energy barrier for the Thr321 pathway is similar to the barrier observed experimentally when Arg418 is removed by mutation. The Thr321 pathway dominates at low pH when Arg418 is protonated, which predicts that the substitution of Glu431 with Gln will shift the pH-rate profile to the right. This prediction is confirmed in subsequent experiments. Phylogenetic analysis suggests that the Thr321 pathway was present in the ancestral enzyme, but was lost when the eukaryotic lineage diverged. We propose that the primordial IMPDH utilized the Thr321 pathway exclusively, and that this mechanism became obsolete when the more sophisticated catalytic machinery of the Arg418 pathway was installed. Thus, our simulations provide an unanticipated window into the evolution of a complex enzyme.https://www.ncbi.nlm.nih.gov/pmc/articles/pmid/18752347/pdf/?tool=EBI |
| spellingShingle | Donghong Min Helen R Josephine Hongzhi Li Clemens Lakner Iain S MacPherson Gavin J P Naylor David Swofford Lizbeth Hedstrom Wei Yang An enzymatic atavist revealed in dual pathways for water activation. PLoS Biology |
| title | An enzymatic atavist revealed in dual pathways for water activation. |
| title_full | An enzymatic atavist revealed in dual pathways for water activation. |
| title_fullStr | An enzymatic atavist revealed in dual pathways for water activation. |
| title_full_unstemmed | An enzymatic atavist revealed in dual pathways for water activation. |
| title_short | An enzymatic atavist revealed in dual pathways for water activation. |
| title_sort | enzymatic atavist revealed in dual pathways for water activation |
| url | https://www.ncbi.nlm.nih.gov/pmc/articles/pmid/18752347/pdf/?tool=EBI |
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