biomolecules Article Revisiting Jatropha curcas Monomeric Esterase: A Dienelactone Hydrolase Compatible with the Electrostatic Catapult Model Marcos Gustavo Araujo Schwarz 1, * , Deborah Antunes 1 , Gabriela Coelho Brêda 2 , Richard Hemmi Valente 3 and Denise Maria Guimarães Freire 4   Citation: Schwarz, M.G.A.; Antunes, D.; Brêda, G.C.; Valente, R.H.; Freire, D.M.G. Revisiting Jatropha curcas Monomeric Esterase: A Dienelactone Hydrolase Compatible with the Electrostatic Catapult Model. Biomolecules 2021, 11, 1486. https:// doi.org/10.3390/biom11101486 Academic Editor: Umesh R. Desai Received: 27 July 2021 Accepted: 11 August 2021 Published: 9 October 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Laboratório de Genômica Funcional e Bioinformática, Instituto Oswaldo Cruz, Fiocruz, Rio de Janeiro 21040900, Brazil; deborah.santos@fiocruz.br 2 Laboratório de Microbiologia Molecular e Proteínas, Departamento de Bioquímica, Instituto de Química, Universidade Federal do Rio de Janeiro, Rio de Janeiro 21941909, Brazil; breda.gabriela@gmail.com 3 Laboratório de Toxinologia, Instituto Oswaldo Cruz, Fiocruz, Rio de Janeiro 21040900, Brazil; richardhemmi@gmail.com 4 Laboratório de Biotecnologia Microbiana, Departamento de Bioquímica, Instituto de Química, Universidade Federal do Rio de Janeiro, Rio de Janeiro 21941909, Brazil; freire@iq.ufrj.br * Correspondence: schwarz@ioc.fiocruz.br; Tel.: +55-21-38658201 Abstract: Jatropha curcas contains seeds with a high oil content, suitable for biodiesel production. After oil extraction, the remaining mass can be a rich source of enzymes. However, data from the literature describing physicochemical characteristics for a monomeric esterase from the J. curcas seed did not fit the electrostatic catapult model for esterases/lipases. We decided to reevaluate this J. curcas esterase and extend its characterization to check this apparent discrepancy and gain insights into the enzyme’s potential as a biocatalyst. After anion exchange chromatography and two-dimensional gel electrophoresis, we identified the enzyme as belonging to the dienelactone hydrolase family, characterized by a cysteine as the nucleophile in the catalytic triad. The enzyme displayed a basic optimum hydrolysis pH of 9.0 and an acidic pI range, in contrast to literature data, making it well in line with the electrostatic catapult model. Furthermore, the enzyme showed low hydrolysis activity in an organic solvent-containing medium (isopropanol, acetonitrile, and ethanol), which reverted when recovering in an aqueous reaction mixture. This enzyme can be a valuable tool for hydrolysis reactions of short-chain esters, useful for pharmaceutical intermediates synthesis, due to both its high hydrolytic rate in basic pH and its stability in an organic solvent. Keywords: Jatropha curcas L.; seed; esterase; dienelactone hydrolase 1. Introduction Jatropha curcas (physic nut)—a plant belonging to the Euphorbiaceae family—has received attention from the scientific community due to its potential in the biodiesel production field [1]. Biofuel generation can be achieved through different methods such as the alkaline transesterification of the seed oil triglycerides with short-chain alcohol (usually methanol or ethanol) [2]. Such technology is quite advantageous due to the good quality of the produced biodiesel. Furthermore, J. curcas can be cultivated on nutrient-poor soils, thus not competing with other crops of agricultural importance [3]. Along with the biodiesel purpose, interest has arisen concerning the remaining mate- rial after the oil extraction, known as the press cake, mainly to use it as animal food due to its high protein content [4]. One drawback of such an approach is the presence of different toxic substances in this material, with phorbol esters being the most harmful for animals [5]. That is why non-toxic J. curcas strains are used for animal feeding purposes. However, this material can also be a source of several enzymes with interesting features. Such is the case for the previously described J. curcas lipase, isolated from the press cake and used in a hybrid (enzymatic/chemical) hydroesterification process for biodiesel production [6]. Biomolecules 2021, 11, 1486. https://doi.org/10.3390/biom11101486 https://www.mdpi.com/journal/biomolecules