Efficient production of (2)H, (13)C, (15)N-enriched industrial enzyme Rhizopus chinensis lipase with native disulfide bonds

Propeptide in Rhizopus chinensis Lipase: New Insights into Its Mechanism of Activity and Substrate Selectivity by Computational Design

Most fungal lipases contain a propeptide, which is very important for their function and substrate selectivity. In the present study, Rhizopus chinensis lipase (RCL) was used as a research model to explore the mechanism of the propeptide of the lipase. Conventional molecular dynamics (MD) and metadynamics simulations were used to explore the mechanism by which the propeptide affects the activity of the lipase, which was subsequently verified by mutation experiments. MD simulations indicated that the propeptide had an inhibitory effect on the lid movement of RCL and found a key region (Val5-Thr10) on the propeptide. Subsequently, site-directed mutations were created in this region. The mutations enhanced the lipase catalytic efficiency to 700% and showed the potential for the propeptide to shift the substrate specificity of RCL. The specificity and activity of RCL mutants also had similar trends to wild-type RCL toward triglycerides with varying chain lengths. The mutual corroboration of simulation and site-directed mutagenesis results revealed the vital role of the key propeptide region in the catalytic activity and substrate specificity of the lipase.

A phenylalanine dynamic switch controls the interfacial activation of Rhizopus chinensis lipase

The catalytic mechanism of most lipases involves a step called "interfacial activation" which significantly increases lipases activity beyond the critical micellar concentration (CMC) of substrate. In the present study, Rhizopus chinensis lipase (RCL) was used as a research model to explore the mechanism of lipase interfacial activation beyond the CMC. Molecular dynamic (MD) simulations indicated the open- and closed-lid transitions and revealed that Phe113 was the critical site for RCL activation by its dynamic flipping. Such putative switch affecting interfacial activation has not been reported in lipase so far. The function of Phe113 was subsequently verified by mutation experiments. The F113W mutant increases the lipase catalytic efficiency (1.9 s^-1·μM^-1) to 280% at the optimum temperature (40 °C) and pH 8.5 with the addition of 0.12 μg protein in the 200 μL reaction system. MD simulations indicated that the fast flipping rate from the closed to the open state, the high open state proportion, and the exposure of the catalytic triad are the main reasons for the lipase activation. The mutual corroboration of simulations and site-directed mutagenesis results revealed the vital role of Phe113 in the lipase activation.

Microbial lipases and their industrial applications: a comprehensive review

Lipases are very versatile enzymes, and produced the attention of the several industrial processes. Lipase can be achieved from several sources, animal, vegetable, and microbiological. The uses of microbial lipase market is estimated to be USD 425.0 Million in 2018 and it is projected to reach USD 590.2 Million by 2023, growing at a CAGR of 6.8% from 2018. Microbial lipases (EC 3.1.1.3) catalyze the hydrolysis of long chain triglycerides. The microbial origins of lipase enzymes are logically dynamic and proficient also have an extensive range of industrial uses with the manufacturing of altered molecules. The unique lipase (triacylglycerol acyl hydrolase) enzymes catalyzed the hydrolysis, esterification and alcoholysis reactions. Immobilization has made the use of microbial lipases accomplish its best performance and hence suitable for several reactions and need to enhance aroma to the immobilization processes. Immobilized enzymes depend on the immobilization technique and the carrier type. The choice of the carrier concerns usually the biocompatibility, chemical and thermal stability, and insolubility under reaction conditions, capability of easy rejuvenation and reusability, as well as cost proficiency. Bacillus spp., Achromobacter spp., Alcaligenes spp., Arthrobacter spp., Pseudomonos spp., of bacteria and Penicillium spp., Fusarium spp., Aspergillus spp., of fungi are screened large scale for lipase production. Lipases as multipurpose biological catalyst has given a favorable vision in meeting the needs for several industries such as biodiesel, foods and drinks, leather, textile, detergents, pharmaceuticals and medicals. This review represents a discussion on microbial sources of lipases, immobilization methods increased productivity at market profitability and reduce logistical liability on the environment and user.

Structural Basis by Which the N-Terminal Polypeptide Segment of Rhizopus chinensis Lipase Regulates Its Substrate Binding Affinity

Members of an important group of industrial enzymes, Rhizopus lipases, exhibit valuable hydrolytic features that underlie their biological functions. Particularly important is their N-terminal polypeptide segment (NTPS), which is required for secretion and proper folding but is removed in the process of enzyme maturation. A second common feature of this class of lipases is the α-helical "lid", which regulates the accessibility of the substrate to the enzyme active site. Some Rhizopus lipases also exhibit "interfacial activation" by micelle and/or aggregate surfaces. While it has long been recognized that the NTPS is critical for function, its dynamic features have frustrated efforts to characterize its structure by X-ray crystallography. Here, we combine nuclear magnetic resonance spectroscopy and X-ray crystallography to determine the structure and dynamics of Rhizopus chinensis lipase (RCL) with its 27-residue NTPS prosequence (r27RCL). Both r27RCL and the truncated mature form of RCL (mRCL) exhibit biphasic interfacial activation kinetics with p-nitrophenyl butyrate (pNPB). r27RCL exhibits a substrate binding affinity significantly lower than that of mRCL due to stabilization of the closed lid conformation by the NTPS. In contrast to previous predictions, the NTPS does not enhance lipase activity by increasing surface hydrophobicity but rather inhibits activity by forming conserved interactions with both the closed lid and the core protein structure. Single-site mutations and kinetic studies were used to confirm that the NTPS serves as internal competitive inhibitor and to develop a model of the associated process of interfacial activation. These structure-function studies provide the basis for engineering RCL lipases with enhanced catalytic activities.

Soluble expression of mature Rhizopus chinensis lipase in Escherichia coli and enhancement of its ester synthesis activity

The production of membrane-associated lipase from Rhizopus chinensis (RCL), which has a high ester synthesis activity and important potential applications, is difficult in heterologous expression system such as Escherichia coli and often leads to the formation of inclusion bodies. Here, we describe the soluble expression of mature RCL (mRCL) using maltose-binding protein (MBP) as a solubility-enhancing tag in the E. coli system. Although the MBP-mRCL fusion protein was soluble, mRCL was insoluble after removal of the MBP tag in E. coli BL21 (DE3). Using E. coli BL21 trxB (DE3) as an expression host, soluble mRCL was obtained and expression conditions were optimized. Furthermore, the ester synthesis activity of soluble mRCL was increased by detergent treatment and was found to be 3.5 and 1.5 times higher than those of the untreated enzyme and naturally occurring enzyme, respectively. Overall, this study provides a potential approach for producing active and soluble forms of eukaryotic lipases in a heterologous E. coli expression system.

Dissecting the Disulfide Linkage of the N-Terminal Domain of HMW 1Dx5 and Its Contributions to Dough Functionality

The N-terminal domain of HMW-GS 1Dx5 (1Dx5-N) contains three cysteine residues (Cys10, Cys25, Cys40), which are the basis of gluten network formation through disulfide bonds. Disulfide linkage in 1Dx5-N was dissected by site-directed mutagenesis and LC-MS/MS, and its contributions to structural and conformational stability of 1Dx5-N and dough functionality were investigated by circular dichroism, intrinsic fluorescence, surface hydrophobicity determination, size exclusion chromatography, nonreducing/reducing SDS-PAGE, atomic force microscopy, and farinographic analysis. Results showed that Cys10 and Cys40 of 1Dx5-N were the active sites for intermolecular linkage. Meanwhile, Cys40 also exhibited the ability to form intrachain disulfide linkage with Cys25. Moreover, Cys10 and Cys40 played a functionally important role in maintaining the structural and conformational stability and high surface hydrophobicity of the N-terminal domain of HMW-GS, which in turn facilitated the formation of HMW polymers and massive disulfide linkage of HMW-GS through hydrophobic interaction. Additionally, the 1Dx5-N mutants in which Cys were replaced by serine (Ser) presented different effects on dough functionality, while only the C25S mutant produced positive effects compared with wild type 1Dx5-N. Na₂CO₃-induced β-elimination of cystine might occur in glutenin without heating, which would make it much easier to reduce the nutritional quality of flour products by the cost of lysine. Therefore, these results give a deep understanding of the disulfide linkage of the N-terminal domain of HMW-GS and its functional importance, which will provide a practical guide to effectively generate a superior HMW-GS allele by artificial mutagenesis.