Metal Ion Promiscuity and Structure of 2,3‐Dihydroxybenzoic Acid Decarboxylase of Aspergillus oryzae

Abstract

Broad substrate tolerance and excellent regioselectivity, as well as independence from sensitive cofactors have established benzoic acid decarboxylases from microbial sources as efficient biocatalysts. Robustness under process conditions makes them particularly attractive for preparative‐scale applications. The divalent metal‐dependent enzymes are capable of catalyzing the reversible non‐oxidative (de)carboxylation of a variety of electron‐rich (hetero)aromatic substrates analogously to the chemical Kolbe‐Schmitt reaction. Elemental mass spectrometry supported by crystal structure elucidation and quantum chemical calculations verified the presence of a catalytically relevant Mg2+ complexed in the active site of 2,3‐dihydroxybenoic acid decarboxylase from Aspergillus oryzae (2,3‐DHBD_Ao). This unique example with respect to the nature of the metal is in contrast to mechanistically related decarboxylases, which generally have Zn2+ or Mn2+ as the catalytically active metal.

Mechanisms of metal-dependent non-redox decarboxylases from quantum chemical calculations

“…11 kcal/mol. This approximation has been applied in all the studies presented here and has been shown to yield satisfactory results [44] , [45] , [46] , [54] .…”

“…Interestingly, Zn was initially proposed to be the divalent metal ion commonly adopted by AHS decarboxylases [33] , [35] , [42] , but Mn was recently determined to be the catalytic metal in LigW [43] , γ-RSD [44] and IDCase [45] . 2,3-DHBD has been shown to be active with both Mn and Mg [46] .…”

“…Crystal structures have been reported for a number of AHS metal-dependent decarboxylases, including the above-mentioned LigW [43] , γ-RSD [33] , [44] , IDCase [45] , and 2,3-DHBD [46] . Comparisons revealed that they have significant structural similarities, in particular the characteristic (β/α) 8 TIM‐barrel fold and the overall active site architectures.…”

“…We have in recent years employed this technique to uncover the reaction mechanisms of the four AHS metal-dependent decarboxylases mentioned above: LigW [54] , γ-RSD [44] , 2,3-DHBD [46] , and IDCase [45] . In this mini-review, we summarize the results of these computational studies, all of which were published in combination with experiments.…”

Synthetic Enzyme‐Catalyzed CO2 Fixation Reactions

“…Several decarboxylases employ divalent metal ions without requiring any organic cofactors. For example, 2,6‐dihydroxybenzoic acid decarboxylases (2,6‐DHBDs) [48] and 2, 3‐DHBDs [49] utilize Zn 2+ and Mg 2+ /Mn 2+ respectively to facilitate the carboxylation of dihydroxybenzenes, while the aliphatic carboxylase, phosphoenolpyruvate carboxylase (PEPC) [50,51] employs either Co 2+ , Mg 2+ , or Mn 2+. in its carboxylation process.…”