<p>Multifunctional enzymes have alternative functions or activities, known as “moonlighting” or “promiscuous”, which are often hidden behind a native enzyme activity and therefore only visible under special environmental conditions. In this thesis, the active-site of Pseudozyma (formerly Candida) antarctica lipase B was explored for a promiscuous conjugate addition activity. Pseudozyma antarctica lipase B is a lipase industrially used for hydrolysis or transacylation reactions. This enzyme contains a catalytic triad, Ser105-His224-Asp187, where a nucleophilic attack from Ser105 on carboxylic acid/ester substrates cause the formation of an acyl enzyme. For conjugate addition activity in Pseudozyma antarctica lipase B, replacement of Ser105 was assumed necessary to prevent competing hemiacetal formation. However, experiments revealed conjugate addition activity in both wild-type enzyme and the Ser105Ala variant. Enzyme-catalyzed conjugate additions were performed by adding sec-amine, thiols or 1,3-dicarbonyl compounds to various α,β-unsaturated carbonyl compounds in both water or organic solvent. The reactions followed Michaelis-Menten kinetics and the native ping pong bi bi reaction mechanism of Pseudozyma antarctica lipase B for hydrolysis/transacylation was rerouted to a novel ordered bi uni reaction mechanism for conjugate addition (Paper I, II, III). The lipase hydrolysis activity was suppressed more than 1000 times by the replacement of the nucleophilic Ser105 to Ala (Paper III).</p>

Recombinant Candida antarctica lipase B was successfullyproduced in the methylotropic yeast Pichia pastoris. Thespecific activities of Candida antarctica lipase B produced inPichia pastoris and commercial Candida antarctica lipase B fromNovozymes were the same. In shake-flask cultivations theexpression levels were about 25 mg L-1. Production levels couldbe increased to 1.5 g L-1, using a fermentor. A model tosimulate growth and oxygen consumption was described. The highcell density growth could be explained by the low maintenancecoefficient of Pichia pastoris. Enrichment of the aeration withoxygen increased the recombinant protein production. The lipasewas also produced as a fusion to a cellulose binding module.The cellulose binding module did not interfere with thespecific activity of the lipase. With this fusion proteincatalytic reactions can be performed in close proximity to acellulose surface. The binding module can also function as anaffinity tag for purification. Establishment of the Candidaantarctica lipase B production system allowed the engineeringof Candida antarctica lipase B variants. Four differentvariants were produced in order to investigate if electrostaticinteractions contributed to enantioselectivity. Theenantioselectivity of two halogenated secondary alcohols wasdoubled for the Ser47Ala variant. Thisimplied thatelectrostatic interactions are important forenantioselectivity. The Trp104His variant showed a decrease inenantioselectivity for all tested substrates. This was causedby an increase in the size of the stereoselectivity pocket.Symmetrical secondary alcohols of different size were used tomap the stereoselectivity pocket. A substituent as large as apropyl or isopropyl could be accommodated in the pocket of theTrp104His variant. In the wild-type lipase thestereoselectivity pocket was estimated to fit an ethyl group.The enzyme variants were subjected to a thermodynamic study, toelucidate changes in the enthalpic and entropic contributionsto enantioselectivity. The enthalpic and entropic contributionschanged for the different lipase variants and werecompensatory. The compensation was not perfect, allowing forchanges in enantioselectivity. In general one can conclude that rational design of newenzyme properties, in order to change the substrateselectivity, is feasible if based on a thorough model ofsubstrate enzyme interactions. <b>Key words:</b>Protein expression, Candida antarctica lipaseB, Pichia pastoris, sitedirected mutagenesis, fermentation,selectivity

The substrate selectivities for different serine hydrolases were utilized in various applications, presented in papers I-VI. The articles are discussed in the thesis in view of the kinetics of the enzyme catalysis involved. In paper I the enantioselectivities towards a range of secondary alcohols were reversed for Candida antarctica lipase B by site directed mutagenesis. The thermodynamic components of the enantioselectivity were determined for the mutated variant of the lipase. In papers II-III Candida antarctica lipase B was engineered for selective monoacylation using two different approaches. A variant of the lipase created for substrate assisted catalysis (paper II) and three different variants with mutations which decreased the volume of the active site (paper III) were evaluated. Enzyme kinetics for the different variants were measured and translated into activation energies for comparison of the approaches. In papers IV and V three different enzymes were used for rapid analysis of enantiomeric excess and conversion of O-acylated cyanohydrins synthesized by a defined protocol. Horse liver alcohol dehydrogenase, Candida antarctica lipase B and pig liver esterase were sequentially added to a solution containing the O-acylated cyanohydrin. Each enzyme caused a drop in absorbance from oxidation of NADH to NAD+. The product yield and enantiomeric excess was calculated from the relative differences in absorbance. In paper VI a method for C-terminal peptide sequencing was developed based on conventional Carboxypeptidase Y digestion combined with matrix assisted laser desorption/ionization mass spectrometry. An alternative nucleophile was used to obtain a stable peptide ladder and improve sequence coverage. / QC20100629

In a lipase investigation, Candida antarctica lipase B (CALB) are explored for enzyme catalytic promiscuity. Enzyme catalytic promiscuity is shown by enzymes catalyzing alternative catalytic transformations proceeding via different transition state structures than normal. CALB normally performs hydrolysis reactions by activating and coordinating carboxylic acid/ester substrates in an oxyanion hole prior to nucleophilic attack from an active-site serine resulting in acyl enzyme formation. The idea of utilizing the carbonyl activation oxyanion hole in the active-site of CALB to catalyze promiscuous reactions arose by combining catalytic and structural knowledge about the enzyme with chemical imagination. We choose to explore conjugate addition and direct epoxidation activities in CALB by combining molecular modeling and kinetic experiments. By quantum-chemical calculations, the investigated promiscuous reactions were shown to proceed via ordered reaction mechanisms that differ from the native ping pong bi bi reaction mechanism. The investigated promiscuous activities were shown to take place in the enzyme active-site by various kinetic experiments, but despite this, no enantioselectivity was displayed. The reason for this is unknown, but can be a result of a too voluminous active-site or the lack of covalent coordination of the substrates during enzyme-catalysis (Paper I-IV). Combining enzyme structural knowledge with chemical imagination may provide numerous novel enzyme activities to be discovered. In an ω-transaminase investigation, two (S)-selective ω-transaminases from Arthrobacter citreus (Ac-ωTA) and Chromobacterium violaceum (Cv-ωTA) are explored aiming to improve their catalytic properties. Structural knowledge of these enzymes was provided by homology modeling. A homology structure of Ac-ωTA was successfully applied for rational design resulting in enzyme variants with improved enantioselectivity. Additionally, a single-point mutation reversed the enantiopreference of the enzyme from (S) to (R), which was further shown to be substrate dependent (Paper V). A homology structure of Cv-ωTA guided the creation of an enzyme variant showing reduced isopropyl amine inhibition. / QC20100609

Biocatalysis has become a popular technique in organic synthesis due to high activity and selectivity of enzyme catalyzed reactions. Enantioselectivity is a particularly attractive enzyme property, which is utilized for the production of enantiopure substances. Determination of the temperature dependence of enzyme enantioselectivity allows for thermodynamic analyses that reveal the contribution of differential activation enthalpy, ΔR-SΔH‡, and entropy, ΔR-SΔS‡. In the present investigation the influence of substrate structure, variations on enzyme structure and of reaction media on the enantioselectivity of Candida Antarctica lipase B has been studied. The contribution of enthalpy, ΔR-SΔH‡, and entropy, TΔR-SΔS‡, to the differential free energy, ΔR-SΔG‡, of kinetic resolutions of sec-alcohols were of similar magnitude. Generally the two terms were counteracting, meaning that the enantiomer favored by enthalpy was disfavored by entropy. 3-Hexanol was an exception where the preferred enantiomer was favored both by enthalpy and by entropy. Resolution of 1-bromo-2-butanol revealed non-steric interactions to influence both ΔR-SΔH‡ and ΔR-SΔS‡. Molecular modeling of the spatial freedom of the enzyme-substrate transition state indicated correlation tothe transition state entropy. The acyl chain length was shown to affect enantioselectivity in transesterifications of a sec-alcohol. Point mutations in the active site were found to decrease or increase enantioselectivity. The changes were caused by partly compensatory changes in both ΔR-SΔH‡ and ΔR-SΔS‡. Studies on single and double mutation variants showed that the observed changes were not additive. Enantioselectivity was strongly affected by the reaction media. Transesterifications of a sec-alcohol catalyzed by Candida Antarctica lipase B was studied in eight liquidorganic solvents and supercritical carbon dioxide. A correlation of enantioselectivity and the molecular volume of the solvent was found. Differential activation enthalpy, ΔR-SΔH‡, and entropy, ΔR-SΔS‡, display a compensatory nature. However this compensation is not perfect, which allows for modifications of enantioselectivity. The components of the thermodynamic parameters are highly complex and interdependent but if their roles are elucidated rational design of enantioselective enzymatic processes may be possible. / QC 20100616

Telechelic polyesters have successfully been synthesized with lipase-catalyzed polymerization. The produced telechelics had a high degree of di­functionalization, high purity (requiring little or no workup) and controlled degree of polymerization. The syntheses were performed in one-pot one-step reaction systems. The use of protection/deprotection chemistry was not necessary, since the lipase selectivity was utilized in the syntheses. Two different types of lipase-catalyzed polymerizations were applied – ring-opening polymerization and polycondensation. In ring-opening polymerization telechelics were produced by a combination of initiation, α-functionalization, and linking through termination, w-func­tionalization. In polycondensation different types of end-cappers were used to synthesize telechelics. Several exampels of functional groups were used for end-functionalization - epoxide, methacrylate and tetraallyls. Enzyme kinetic schemes describing the different functionalization met­hods of polyesters are presented and discussed. Stoichiometry and different reaction conditions have been studied to understand the effects these functions have on the final structure of the synthesized telechelics. Polyesters are classified as biodegradable, and can also be synthesized from materials that can be extracted or fermented from renewable sources like plants. Lipase-catalysts have several beneficial attributes, like high selectivity, they are renewable and biodegradable, are non-toxic and metal-free and can operate under mild reaction conditions. The focus of this thesis has been on lipase-catalyzed syntheses and characterization of the produced telechelics, in addition some materials have been produced. Some uses of telechelics are surface modification, materials for block co-polymers, functional films and biomedical applications. / QC20100726

<p>Recombinant Candida antarctica lipase B was successfullyproduced in the methylotropic yeast Pichia pastoris. Thespecific activities of Candida antarctica lipase B produced inPichia pastoris and commercial Candida antarctica lipase B fromNovozymes were the same. In shake-flask cultivations theexpression levels were about 25 mg L-1. Production levels couldbe increased to 1.5 g L-1, using a fermentor. A model tosimulate growth and oxygen consumption was described. The highcell density growth could be explained by the low maintenancecoefficient of Pichia pastoris. Enrichment of the aeration withoxygen increased the recombinant protein production. The lipasewas also produced as a fusion to a cellulose binding module.The cellulose binding module did not interfere with thespecific activity of the lipase. With this fusion proteincatalytic reactions can be performed in close proximity to acellulose surface. The binding module can also function as anaffinity tag for purification. Establishment of the Candidaantarctica lipase B production system allowed the engineeringof Candida antarctica lipase B variants. Four differentvariants were produced in order to investigate if electrostaticinteractions contributed to enantioselectivity. Theenantioselectivity of two halogenated secondary alcohols wasdoubled for the Ser47Ala variant. Thisimplied thatelectrostatic interactions are important forenantioselectivity. The Trp104His variant showed a decrease inenantioselectivity for all tested substrates. This was causedby an increase in the size of the stereoselectivity pocket.Symmetrical secondary alcohols of different size were used tomap the stereoselectivity pocket. A substituent as large as apropyl or isopropyl could be accommodated in the pocket of theTrp104His variant. In the wild-type lipase thestereoselectivity pocket was estimated to fit an ethyl group.The enzyme variants were subjected to a thermodynamic study, toelucidate changes in the enthalpic and entropic contributionsto enantioselectivity. The enthalpic and entropic contributionschanged for the different lipase variants and werecompensatory. The compensation was not perfect, allowing forchanges in enantioselectivity.</p><p>In general one can conclude that rational design of newenzyme properties, in order to change the substrateselectivity, is feasible if based on a thorough model ofsubstrate enzyme interactions.</p><p><b>Key words:</b>Protein expression, Candida antarctica lipaseB, Pichia pastoris, sitedirected mutagenesis, fermentation,selectivity</p>

Pseudozyma (Candida) antarctica lipase B (PalB) was expressed in Escherichia coli facilitating protein engineering. The lack of glycosylation was evaluated for a deeper understanding of the difficulties in expressing PalB in E. coli. Different systems were tested: periplasmic expression in Rosetta (DE3), cytosolic expression in Rosetta-gami 2(DE3), Origami 2(DE3), and coexpression of groES and groEL. Periplasmic expression resulted 5.2 mg/L active PalB at 16 °C in shake flasks. This expression level was improved by using the EnBase technology, enabling fed-batch cultivation in 24-deep well scale. The feed rate was titrated with the addition of α-amylase, which slowly releases glucose as energy source. Different media were evaluated where the EnBase mineral salt medium resulted in 7.0 mg/L of active PalB. Protein secreted directly into the media was obtained using the constitutive glyceraldehyde-3-phosphate dehydrogenase (GAP) promoter for screening and production of PalB in P. pastoris. A protease sensitive fusion protein CBM-PalB (cellulose-binding module) was used as a model system. When optimised, the expression system resulted in 46 mg/L lipase in 72 hours in shake flask, 37 mg/L lipase in 28 hours in 96-deep-well plate format, and 2.9 g PalB per 10 L bioreactor cultivation. The E. coli expression system was used to express a small focused library of PalB variants, designed to prevent water from entering the active site through a hypothesised tunnel. Screening of the library was performed with a developed assay, allowing for simultaneous detection of both transacylation and hydrolytic activity. From the library a mutant S47L, in which the inner part of the tunnel was blocked, was found to catalyse transacylation of vinyl butyrate in 20 mM butanol 14 times faster than hydrolysis. Water tunnels, assisting water in reaching the active sites, were furthermore found by molecular modelling in many hydrolases. Molecular modelling showed a specific water tunnel in PalB. This was supported by experimental data, where the double mutant Q46A S47L catalysed transacylation faster than hydrolysis compared to the wild type PalB. / <p>QC 20100818</p>

Neste trabalho, duas preparações de lipase imobilizada (EC 3.1.1.3), tipo B (CALB) de Candida antarctica, foram comparadas como biocatalisadores na síntese de ésteres metílicos. CALB imobilizada comercialmente (Novozym 435 - CALB-435) e CALB imobilizada em esferas de estireno-divinilbenzeno (CALB-MCI) foram testadas para as reações de transesterificação. Um delineamento composto central rotacional (DDCR) e metodologia de superfície de resposta (MSR) foram utilizados para otimizar a relação razão molar álcool:óleo, teor de enzimas, e a água adicionada nas reações. As duas preparações de enzimas mostraram diferentes condições ótimas para a produção de ésteres metílicos, com a taxa inicial da reação de 51,47 mmol L-1 h-1 para CALB-435, e 57 mmol L-1 h-1 para CALB-MCI. O estudo do tempo de reação indicou que em 72 h foi possível obter conversões próximas a 100 % para ambos os derivados. Um alto rendimento de conversão foi obtido sob as condições otimizadas, indicando que a RSM pode ser usada para descrever adequadamente a relação entre os parâmetros de reação e da resposta (teor de ésteres metílicos). Sobre a estabilidade operacional durante as experiências de reutilização, ambos preparados enzimáticos mantiveram 70 % de sua atividade inicial após oito bateladas, sugerindo sua aplicabilidade na produção de biodiesel. / In this work two preparations of immobilized lipase (EC 3.1.1.3), type B (CALB) from Candida antarctica, were compared as biocatalysts in the synthesis of esters. Commercial Novozym 435 (CALB-435) and CALB immobilized on styrene-divinylbenzene beads (CALB-MCI) were tested for the transesterification reactions. Central composite design rotational (DCCR) and response surface methodology (RSM) were used to optimize the substrate molar ratio, enzyme content, and the added water. The two enzyme preparations have shown different optimal conditions for the production of methyl esters, with initial rates of reaction 51.47 mmol L-1 h-1 for CALB-435, and 57 mmol L-1 h-1 for CALB-MCI. The study of reaction time indicated that in 72 h it was possible to obtain conversions close to 100 % for both derivatives. A high yield conversion was obtained under the optimized conditions, indicating that RSM can be used to adequately describe the relationship between the reaction parameters and the response (yield conversion) in lipase-catalyzed biodiesel synthesis. Over the operational stability during experiments of batch reuse, both prepared enzymatic maintained 70 % of their initial activity after eight batches, suggesting their potential for economical application on biodiesel production.

Neste trabalho, duas preparações de lipase imobilizada (EC 3.1.1.3), tipo B (CALB) de Candida antarctica, foram comparadas como biocatalisadores na síntese de ésteres metílicos. CALB imobilizada comercialmente (Novozym 435 - CALB-435) e CALB imobilizada em esferas de estireno-divinilbenzeno (CALB-MCI) foram testadas para as reações de transesterificação. Um delineamento composto central rotacional (DDCR) e metodologia de superfície de resposta (MSR) foram utilizados para otimizar a relação razão molar álcool:óleo, teor de enzimas, e a água adicionada nas reações. As duas preparações de enzimas mostraram diferentes condições ótimas para a produção de ésteres metílicos, com a taxa inicial da reação de 51,47 mmol L-1 h-1 para CALB-435, e 57 mmol L-1 h-1 para CALB-MCI. O estudo do tempo de reação indicou que em 72 h foi possível obter conversões próximas a 100 % para ambos os derivados. Um alto rendimento de conversão foi obtido sob as condições otimizadas, indicando que a RSM pode ser usada para descrever adequadamente a relação entre os parâmetros de reação e da resposta (teor de ésteres metílicos). Sobre a estabilidade operacional durante as experiências de reutilização, ambos preparados enzimáticos mantiveram 70 % de sua atividade inicial após oito bateladas, sugerindo sua aplicabilidade na produção de biodiesel. / In this work two preparations of immobilized lipase (EC 3.1.1.3), type B (CALB) from Candida antarctica, were compared as biocatalysts in the synthesis of esters. Commercial Novozym 435 (CALB-435) and CALB immobilized on styrene-divinylbenzene beads (CALB-MCI) were tested for the transesterification reactions. Central composite design rotational (DCCR) and response surface methodology (RSM) were used to optimize the substrate molar ratio, enzyme content, and the added water. The two enzyme preparations have shown different optimal conditions for the production of methyl esters, with initial rates of reaction 51.47 mmol L-1 h-1 for CALB-435, and 57 mmol L-1 h-1 for CALB-MCI. The study of reaction time indicated that in 72 h it was possible to obtain conversions close to 100 % for both derivatives. A high yield conversion was obtained under the optimized conditions, indicating that RSM can be used to adequately describe the relationship between the reaction parameters and the response (yield conversion) in lipase-catalyzed biodiesel synthesis. Over the operational stability during experiments of batch reuse, both prepared enzymatic maintained 70 % of their initial activity after eight batches, suggesting their potential for economical application on biodiesel production.