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Publication Abstract from PubMed

Lactones are prevalent in biological and industrial settings, yet there is a lack of information regarding enzymes used to metabolize these compounds. One compound, gamma-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 Ca(2+)-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 beta-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 wild type 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 beta-propeller lactonases suggests this mechanism may be relevant for other members of this emerging class of versatile catalysts.

A broad specificity beta-propeller enzyme from Rhodopseudomonas palustris that hydrolyzes many lactones including gamma-valerolactone.,Hall BW, Bingman CA, Fox BG, Noguera DR, Donohue TJ J Biol Chem. 2022 Dec 8:102782. doi: 10.1016/j.jbc.2022.102782. PMID:36502920^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.