9h4h
trans-aconitate decarboxylase Tad1_S320A
Structural highlights
FunctionTAD1_MYCMD Trans-aconitate decarboxylase; part of the gene cluster that mediates the biosynthesis of itaconic acid and 2-hydroxyparaconate (PubMed:26639528, PubMed:27750034). Cis-aconitate is secreted by the mitochondrial tricarboxylate transporter MTT1. In the cytosol cis-aconitate is converted into trans-aconitate via isomerization by the aconitate-delta-isomerase ADI1 (PubMed:26639528). Decarboxylation of trans-aconitate by the trans-aconitate decarboxylase TAD1 then leads then to the production of itaconic acid (PubMed:26639528). The cytochrome P450 monooxygenase CYP3 further converts itaconate to 2-hydroxyparaconate via oxidation of the double bond, leading to a transient epoxide, which can subsequently be lactonized to produce 2-hydroxyparaconate (PubMed:27750034). Secretion of itaconate and possibly 2-hydroxyparaconate into the medium is mediated by the major facilitator ITP1 (PubMed:26639528, PubMed:27750034). The glyoxalase domain-containing protein RDO1 is not involved in the biosynthesis of itaconate and 2-hydroxyparaconate, however, it might play a role in the further conversion of 2-hydroxyparaconate to itatartarate (PubMed:27750034).[1] [2] Publication Abstract from PubMedItaconic acid belongs to the high-value precursors for the production of biomass-based industrial compounds. It originates from the tricarboxylic acid cycle, and depending on the organism, it is produced by different biosynthetic routes. The basidiomycete fungus Ustilago maydis synthesizes itaconic acid via isomerization of cis-aconitic acid to trans-aconitic acid, and subsequent decarboxylation catalyzed by the trans-aconitate decarboxylase Tad1, which belongs to the aspartase/fumarase superfamily. Since no other decarboxylase has been identified within this protein superfamily, Tad1 constitutes a novel type of decarboxylase. Here, we present high-resolution crystal structures of Tad1, which, together with mutational analysis and nuclear magnetic resonance spectroscopy measurements, provide insight into the molecular mechanism of Tad1-dependent decarboxylation. Specifically, our study shows that decarboxylation is favored in acidic conditions, requires protonation as well as migration of a double bond, and coincides with structural rearrangements in the catalytic center. In summary, our study elucidates the molecular mechanism underlying a novel type of enzymatic decarboxylation and provides a starting point for protein engineering aimed at optimizing the efficient production of itaconic acid. Mechanistic and structural insights into the itaconate-producing trans-aconitate decarboxylase Tad1.,Zheng L, Li W, Christ M, Paczia N, Buckel W, Mais CN, Bolker M, Freitag J, Bange G PNAS Nexus. 2025 Mar 5;4(3):pgaf059. doi: 10.1093/pnasnexus/pgaf059. eCollection , 2025 Mar. PMID:40045995[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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