Influence of lid conformation on lipase enantioselectivity

Overexpression and truncation of a novel cold-adapted lipase with improved enzymatic characteristics

The novel cold-adapted lipase (Lip ZC12) derived from Psychrobacter sp. ZY124 exhibited higher catalytic activity at 20-40 °C, the whole gene was then sequenced, analyzed, and overexpressed. However, its intrinsic structural characteristics lead to a decreased affinity toward the substrate, thus limiting the improvement of catalytic efficiency. Modeling the homologous structure and simulating the binding process of Lip ZC12 with the substrate. It was found that truncated lid (lip-Δlid) could not only increase the kcat, but also significantly enhance the substrate affinity, the substrate affinity and catalytic efficiency of Lip ZC12 modified by lid truncation were significantly improved. The results revealed that the kcat/Km value of lip-Δlid was 1.6 times higher than that of free lipase. This improved catalytic performance of cold-adapted lipase, and these findings laid an important foundation for further application.

Identification and Heterologous Production of a Lipase from Geobacillus kaustophilus DSM 7263T and Tailoring Its N-Terminal by a His-Tag Epitope

Lipases are versatile biocatalysts with many biotechnological applications and the necessity of screening, production and characterization of new lipases from diverse microbial strains to meet industrial needs is constantly emerging. In this study, the lipase gene (gklip) from a thermophilic bacterium, Geobacillus kaustophilus DSM 7263 ^T was cloned into the pET28a ( +) vector with N-terminal 6xHis-tag. The recombinant gklip gene was heterologously expressed in host E. coli BL21 (DE3) cells and purified by Ni-NTA affinity chromatography. Histidine tag was removed from the purified 6xHistag-Gklip enzyme with thrombin enzyme and the molecular mass was determined to be approximately 43 kDa by SDS-PAGE. Gklip showed optimal activity at pH 8.0 and 50 °C. The specific hydrolytic activities against substrates were significantly increased by the removal of the His-tag. K_m and k_cat values of Gklip against p-nitrophenyl palmitate (pNPP, 4-nitrophenyl palmitate) as the target substrate were found to be as 1.22 mM and 417.1 min^-1, respectively. Removing His-tag changed the substrate preference of the enzyme leading to maximum lipolytic activity towards C10 and C12 lipids. Similarly, the activity against coconut oil that containing 62% medium-chain fatty acids was significantly higher than other oils. Furthermore, preservation of activity in the presence of inhibitors, organic solvents support the effect of lid structure of the enzyme.

Activation of Lipase-Catalyzed Reactions Using Ionic Liquids for Organic Synthesis

The use of ionic liquids to replace organic or aqueous solvents in biocatalysis processes has recently received great attention, and much progress has been made in this area; the lipase-catalyzed reactions are the most successful. Recent developments in the application of ionic liquids as solvents in lipase-catalyzed reactions for organic synthesis are reviewed, focusing on the ionic liquid mediated activation method of lipase-catalyzed reactions.

Self-Assembly Nanostructures of Triglyceride-Water Interfaces Determine Functional Conformations of Candida antarctica Lipase B

Candida antarctica lipase B (CalB) acts as a lipase when adsorbed to an acylglyceride interface and as an esterase when exposed to an aqueous environment. The effect of the molecular self-assembly nanostructure of triglyceride-water interfaces on structural conformations of adsorbed CalB and the implications to its catalytic function were studied by molecular dynamics simulations. Systems of CalB adsorbed to interfaces and solvated in water were compared. The two environments induced relative motions of helices α5 and α10 that resulted in open and closed conformations. The open conformation was stabilized by interactions between the polar and nonpolar amino acids of α5 and α10 and the nanostructure of triglyceride aggregates, which self-assembled into crystalline-like patterns of alternating polar and nonpolar lamellae. Thus, the structure of CalB has been adapted by evolution to the geometric constraints imposed by the interface nanostructure for optimized catalytic activity. Helices α5 and α10 have two functions. As mobile elements, they ensure access of bulky substrates to the active site in the open conformation. As a part of the active site pocket, they ensure binding of substrate molecules in a productive orientation near the active site. In water, access to the binding site is limited, and the smaller substrate binding site is beneficial for the binding of small, water-soluble substrates. The CalB crystal structure commonly used for protein engineering studies represents an intermediate state between open and closed, and may thus not be adequate to assess the function of CalB, neither as lipase nor as esterase.

Interfacial Activation of Candida antarctica Lipase B: Combined Evidence from Experiment and Simulation

Lipase immobilization is frequently used for altering the catalytic properties of these industrially used enzymes. Many lipases bind strongly to hydrophobic surfaces where they undergo interfacial activation. Candida antarctica lipase B (CalB), one of the most commonly used biocatalysts, is frequently discussed as an atypical lipase lacking interfacial activation. Here we show that CalB displays an enhanced catalytic rate for large, bulky substrates when adsorbed to a hydrophobic interface composed of densely packed alkyl chains. We attribute this increased activity of more than 7-fold to a conformational change that yields a more open active site. This hypothesis is supported by molecular dynamics simulations that show a high mobility for a small "lid" (helix α5) close to the active site. Molecular docking calculations confirm that a highly open conformation of this helix is required for binding large, bulky substrates and that this conformation is favored in a hydrophobic environment. Taken together, our combined approach provides clear evidence for the interfacial activation of CalB on highly hydrophobic surfaces. In contrast to other lipases, however, the conformational change only affects large, bulky substrates, leading to the conclusion that CalB acts like an esterase for small substrates and as a lipase for substrates with large alcohol substituents.

Construction of Aspergillus niger lipase mutants with oil-water interface independence

Based on previous bioinformational analytical results [Shu ZY, et al. Biotechnol Prog 2009;25:409-16], four A. niger lipase (ANL) mutants, ANL-Ser84Gly, ANL-Asp99Pro, ANL-Lys108Glu and ANL-EαH (obtained by replacing the lid domain of ANL with the corresponding domain from A. niger feruloyl esterase), were constructed to screen out ANL mutants with oil-water interface independence. ANL-S84G displayed a pronounced interfacial activation, while ANL-D99P and ANL-K108E displayed no interfacial activation. The specific activity of ANL-S84G towards p-nitrophenyl esters decreased from 29.8% to 76.5% compared with that of ANL, while the specific activity of ANL-D99P towards p-nitrophenyl palmitate increased 2.2-fold. The thermostability of ANL-K108E was almost unchanged, while the thermostability of ANL-S84G and ANL-D99P significantly decreased compared with that of ANL. The construction of oil-water interface-independent ANL mutants would help to further understand the mechanism of lipase interfacial activation.

Functional fusion mutant of Candida antarctica lipase B (CalB) expressed in Escherichia coli

Candida antarctica lipase B (CalB) was functionally expressed in the cytoplasm of Escherichia coli Origami(DE3) with the N-terminus fusion of E. coli endogenous proteins. The previously-identified stress responsive proteins through comparative proteome analyses such as malate dehydrogenase (Mdh), spermidine/putrescine-binding periplasmic protein (PotD), and FKBP-type peptidyl-prolyl cis-trans isomerase (PPIases) (SlyD) dramatically increased the solubility of CalB in E. coli cytoplasm when used as N-terminus fusion partners. We demonstrated that Mdh, PotD, and SlyD were powerful solubility enhancers that presumably facilitated the protein folding of CalB. Moreover, among the various fusion mutants, Mdh-CalB showed the highest hydrolytic activity and was as biologically active as standard CalB. Similarly to the previous report, the electrophoretic properties of CalB indicate that CalB seems to form dimer-based oligomer structures. We evaluated the structural compatibility between the fusion partner protein and CalB, which seems to be of crucial importance upon the bioactive dimer formation of CalB and might affect the substrate accessibility to the enzyme active site, thereby determining the biological activities of the fusion mutants.

Gene cloning, expression, and characterization of the Geobacillus Thermoleovorans CCR11 thermoalkaliphilic lipase

The gene for a Geobacillus thermoleovorans CCR11 thermostable lipase was recovered by PCR and cloned. Four genetic constructions were designed and successfully expressed in E. coli: (i) the lipase structural gene (lipCCR11) in the PinPoint Xa vector; (ii) the lipase structural gene (lipACCR11) in the pET-28a(+) vector; (iii) the lipase structural gene minus the signal peptide (lipMatCCR11) in the pET-3b vector; and (iv) the lipase structural gene plus its own promoter (lipProCCR11) in the pGEM-T cloning vector. The lipase gene sequence analysis showed an open reading frame of 1,212 nucleotides coding for a mature lipase of 382 residues (40 kDa) plus a 22 residues signal peptide. Expression under T7 and T7lac promoter resulted in a 40- and 36-fold increase in lipolytic activity with respect to the original strain lipase. All recombinant lipases showed an optimal activity at pH 9.0, but variations were found in the temperature for maximum activity and the substrate specificity among them and when compared with the parental strain lipase, especially in the recombinant lipases that contained fusion tags. Therefore, it is important to find the appropriate expression system able to attain a high concentration of the recombinant lipase without compromising the proper folding of the protein.

Glutaraldehyde Cross-Linking of Lipases Adsorbed on Aminated Supports in the Presence of Detergents Leads to Improved Performance

Lipases from Candida rugosa (CRL) and lipase isoforms A and B from Candida antarctica (CAL-A and CAL-B) were adsorbed on aminated supports in the presence of detergents to have individual lipase molecules. Then, one fraction was washed to eliminate the detergent, and both preparations were treated with glutaraldehyde. The presence of detergent during the cross-linking of the lipases to the support permitted an increase in the recovered activity (in some instances, even by a 10-fold factor). This activity was higher even than that exhibited by the just adsorbed lipases, suggesting that it was not a result of some protective effect of the detergent in the enzyme activity during glutaraldehyde chemical modification. Moreover, the enantioselectivity of the different enzyme preparations was very different if the glutaraldehyde was offered in the presence or in the absence of detergent, in some cases increasing the E value (even by a 7-fold factor in the case of CAL-A in the hydrolysis of (+/-)-2-hydroxy-4-phenylbutyric acid ethyl ester), in other cases even inverting the enantio preference (e.g., in the case of CRL). The irreversible chemical inhibition of the enzyme that was immobilized and cross-linked with glutaraldehyde in the presence of detergents was more rapid than that in the other preparations (by more than a 10-fold factor). This experiment reveals an exposition degree of the active serine in the preparation cross-linked with the support in the presence of detergent that is higher than that in the other preparations. The results suggested that different enzyme structures were "stabilized" by the glutaraldehyde treatment if performed in the presence or in the absence of detergent, and that, in the presence of detergent, a form of the lipase with the serine residue more exposed to the medium and much more active could be obtained. This strategy seems to be of general use to improve the lipase activity to be used in macroaqueous media.

Functional expression of Candida antarctica lipase B in Eschericha coli

Candida antarctica lipase B (CalB) is an important catalyst in bio-organic synthesis. To optimize its performance, either the reaction medium is changed or the lipase itself is modified. In the latter case, mutants are generated in Eschericha coli and subsequently expressed in fungal hosts for their characterization. Here we present the functional expression of CalB in the periplasm of E. coli. By step-wise deletion of the CalB signal and propeptide we were able to express and purify two different variants of CalB (mature CalB and CalB with its propeptide). A N-terminal FLAG and a C-terminal His tag were used for the purification. For the substrates para-nitrophenol butyrate (p-NPB), para-nitrophenol laurate (p-NPL) and carboxyfluorescein diacetate (CFDA) the specific activity was shown to be similar to CalB expressed in Aspergillus oryzae. The kinetic constants k(M), v(max) and k(cat) were determined using the substrates p-NPB and p-NPL. Almost identical k(cat)/k(M) values (0.423-0.466 min(-1) microM(-1) for p-NPB and 0.068-0.071 min(-1) microM(-1) for p-NPL) were obtained for the CalB variants from E. coli and A. oryzae. The results clearly show that CalB can be functionally expressed in E. coli and that the attachment of tags does not alter the properties of the lipase.

Understanding Candida rugosa lipases: an overview

Candida rugosa lipase (CRL) is one of the enzymes most frequently used in biotransformations. However, there are some irreproducibility problems inherent to this biocatalyst, attributed either to differences in lipase loading and isoenzymatic profile or to other medium-engineering effects (temperature, a(w), choice of solvent, etc.). In addition, some other properties (influence of substrate and reaction conditions on the lid movement, differences in the glycosylation degree, post-translational modifications) should not be ruled out. In the present paper the recent developments published in the CRL field are overviewed, focusing on: (a) comparison of structural and biochemical data among isoenzymes (Lip1-Lip5), and their influence in the biocatalytical performance; (b) developments in fermentation technology to achieve new crude C. rugosa lipases; (c) biocatalytical reactivity of each isoenzyme, and methods for characterising them in crude CRL; (d) state-of-the-art of new applications performed with recombinant CRLs, both in CRL-second generation (wild-type recombinant enzymes), as well as in CRL-third generation, (mutants of the wt-CRL).

Activity and enantioselectivity of wildtype and lid mutated Candida rugosa lipase isoform 1 in organic solvents

The activity and enantioselectivity of lipase 1 from Candida rugosa and of a chimera enzyme obtained by replacing the lid of isoform 1 with the lid of isoform 3 were compared in organic solvents. The alcoholysis of chloro ethyl 2-hydroxy hexanoate with methanol and of vinyl acetate with 6-methyl-5-hepten-2-ol were used as model reactions in different reaction conditions. The chimera enzyme was less active and enantioselective than the wildtype in all the conditions tested. A rationale for such decreases could be that the chimera lipase has a lower proportion of enzyme molecules in the open form. This might lead to a hindered access to the enzyme active site, thus affecting the catalytic activity.