Novel Lipases: Expression and Improvement for Applied Biocatalysis = Nuevas lipasas: expresión y mejoras para biocatálisis aplicada

Abstract

This thesis is focused in the identification and improvement of lipases for biotechnological application. The importance of lipases is increasing in several industries. However, the commercial use of lipases is still a drawback in the economics of the lipase-based industrial applications. There are many tools for improving and adapting the enzyme properties to the desired requirements of a process that could lead lipase catalysis through a cost-effective process. In this context, the main objective of this work was: “To characterize, express and to improve novel bacterial lipases for sustainable industrial processes”. The first activity done was to explore and to characterize a new esterase from P. barcinonensis. It was isolate from P. barcinonensis the gene corresponding to Est23, and its cloning in a proper vector to perform expression and purification for biochemical characterization. Est23 showed preference for mid-chain substrates and having maximum activity at 37 °C and pH 7. It also includes in silico analysis of the 3D model structure and phylogeny. Moreover, a phylogenetic tree was constructed to assign Est23 to one of the bacterial hydrolase families described by Arpingy and Jaeger. Est23 could not be assigned to any bacterial hydrolases described till that moment, suggesting that Est23 could be part of a new group of bacterial lipases. Because Est23 displays a GGG(A)X-type putative oxyanion hole, widely described as a motif involved in tertiary alcohol resolution, the ability of Est23 for conversion and resolution of tertiary alcohols was evaluated. However, no conversion was detected using the esters linalyl and terpinyl acetate alcohols as substrates. To improve LipR activity by protein engineering LipR was then desired. LipR was isolated from Rhodococcus sp. strain CR-53 in a previous and showed an unusual fungal-like oxyanion-hole never found among bacterial lipases, close to the Y-type oxyanion hole described for Candida antartica lipase A (CalA), a lipase widely used in industry. In order to improve LipR activity on long-chain substrates, several enzyme-engineering approaches were done to change the amino acids constituting the rare oxyanion hole of LipR for further industrial application. These mutations also allowed studying the role of the amino acids forming the oxyanion hole of LipR. Hydrolytic activity over short, mid and long- chain substrates was assayed with the variants obtained. The LipR variant Asp111Gly produced a change on the chain- length- substrate preference of LipR, displaying a 5.6 fold increase of activity on muf-oleate. This improvement of activity on longer chain length substrates makes of this LipR variant a very attractive candidate for testing activity on biodiesel synthesis, a process requiring activity on long-chain substrates. Nevertheless, LipR and LipR_YGS variant need a clear expression enhancement in order to apply them to transesterification reactions using oily feedstocks. The stabilization Pseudomonas lipases LipA, LipC and LipCmut was improved by immobilization in order to applied these enzymes in transesterification reactions. Therefore, a fast and economic immobilization procedure by adsorption was set up. Finally, the three immobilized lipase preparations and a commercial lipase were used to test alternative feedstocks for triglyceride transesterification. A total of four oils were tested: commercial triolein, degummed soybean oil, waste cooking oil, and Mucor circinelloides oil. Moreover, the characterization of the tested raw materials in terms of FFAs, tri, di and monoglyceride contents measure was also of interest. In a global analysis, a good increase of FAMEs percent was obtained with LipA, LipC and LipCmut immobilized on Accurel MP1000. But better results were achieved when the reactions were catalyzed by Novozym® 435 commercial enzyme.

Esta tesis se centra en la identificación y mejora de lipasas para aplicaciones biotecnológicas. El objetivo principal de este trabajo fue: "Caracterizar, expresar y mejorar las nuevas lipasas bacterianas para procesos industriales sostenibles". La primera actividad realizada fue explorar y caracterizar una nueva esterasa, Est23, de P. barcinonensis. Se aisló de P. barcinonensis el gen correspondiente a Est23 y su clonación en un vector adecuado para realizar la expresión y purificación para caracterización bioquímica. Además, se construyó un árbol filogenético para asignar Est23 a una de las familias de hidrolasas bacterianas descritas por Arpingy y Jaeger, y debido a que Est23 tiene un oxyanion-hole de tipo GGG (A) X, ampliamente descrito como motivo implicado en la resolución del alcohol terciario, se evaluó la capacidad de Est23 en dichas reacciones. Luego se buscó mejorar la actividad sobre sustratos de cadena larga de la lipasa LipR de Rhodococcus sp. por ingeniería de proteínas. Diferentes enfoques de ingeniería enzimática se realizaron para cambiar los aminoácidos que forman parte del atípico oxyanion-hole de LipR. Estas mutaciones también permitieron estudiar el papel de los aminoácidos que forman este motivo. La actividad hidrolítica de las variantes obtenidas fue ensayada sobre sustratos de cadena corta, media y larga. La variante LipR Asp111Gly produjo un cambio en la preferencia de LipR de longitud de cadena. Sin embargo, LipR y LipR_YGS necesitan un aumento de expresión para aplicarlos a reacciones de transesterificación. La estabilización de tres lipasas de Pseudomonas, LipA, LipC y LipCmut, se mejoró por inmovilización con el fin de aplicar estas enzimas en las reacciones de transesterificación. Por lo tanto, se estableció un procedimiento de inmovilización por adsorción rápido y económico. Finalmente, se usaron las tres lipasa inmovilizadas y una lipasa comercial para probar materias primas alternativas para la transesterificación de triglicéridos. Se probaron un total de cuatro aceites: trioleína comercial, aceite de soja desgomado, aceite de cocina de desecho y aceite de Mucor circinelloides. Además se realizó la caracterización de las materias primas ensayadas en términos de la medida de los ácidos grasos, tri, di y monoglicéridos.