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Hall BW, Bingman CA, Fox BG, Noguera DR, Donohue TJ. A broad specificity β-propeller enzyme from Rhodopseudomonas palustris that hydrolyzes many lactones including γ-valerolactone. J Biol Chem 2023; 299:102782. [PMID: 36502920 PMCID: PMC9843451 DOI: 10.1016/j.jbc.2022.102782] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2022] [Revised: 11/30/2022] [Accepted: 12/03/2022] [Indexed: 12/13/2022] Open
Abstract
Lactones are prevalent in biological and industrial settings, yet there is a lack of information regarding enzymes used to metabolize these compounds. One compound, γ-valerolactone (GVL), is used as a solvent to dissolve plant cell walls into sugars and aromatic molecules for subsequent microbial conversion to fuels and chemicals. Despite the promise of GVL as a renewable solvent for biomass deconstruction, residual GVL can be toxic to microbial fermentation. Here, we identified a Ca2+-dependent enzyme from Rhodopseudomonas palustris (Rpa3624) and showed that it can hydrolyze aliphatic and aromatic lactones and esters, including GVL. Maximum-likelihood phylogenetic analysis of other related lactonases with experimentally determined substrate preferences shows that Rpa3624 separates by sequence motifs into a subclade with preference for hydrophobic substrates. Additionally, we solved crystal structures of this β-propeller enzyme separately with either phosphate, an inhibitor, or a mixture of GVL and products to define an active site where calcium-bound water and calcium-bound aspartic and glutamic acid residues make close contact with substrate and product. Our kinetic characterization of WT and mutant enzymes combined with structural insights inform a reaction mechanism that centers around activation of a calcium-bound water molecule promoted by general base catalysis and close contacts with substrate and a potential intermediate. Similarity of Rpa3624 with other β-propeller lactonases suggests this mechanism may be relevant for other members of this emerging class of versatile catalysts.
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Affiliation(s)
- Benjamin W Hall
- Laboratory of Genetics, University of Wisconsin-Madison, Madison, Wisconsin, USA; Department of Energy Great Lakes Bioenergy Research Center, Madison, Wisconsin, USA; Wisconsin Energy Institute, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Craig A Bingman
- Department of Energy Great Lakes Bioenergy Research Center, Madison, Wisconsin, USA; Department of Biochemistry, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Brian G Fox
- Department of Energy Great Lakes Bioenergy Research Center, Madison, Wisconsin, USA; Department of Biochemistry, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Daniel R Noguera
- Department of Energy Great Lakes Bioenergy Research Center, Madison, Wisconsin, USA; Wisconsin Energy Institute, University of Wisconsin-Madison, Madison, Wisconsin, USA; Department of Civil and Environmental Engineering, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Timothy J Donohue
- Department of Energy Great Lakes Bioenergy Research Center, Madison, Wisconsin, USA; Wisconsin Energy Institute, University of Wisconsin-Madison, Madison, Wisconsin, USA; Department of Bacteriology, University of Wisconsin-Madison, Madison, Wisconsin, USA.
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