Structure and function of lipases

The transcription factor CREB3-2 regulated neutral lipase gene expression in ovary of Nilaparvata lugens

The cyclic AMP-responsive element-binding protein 3 (CREB3) members have unique regulatory roles in cellular lipid metabolism as transcription factors. Two CREB3 proteins in Nilaparvata lugens were identified and analyzed. In ovary, when silencing NlCREB3-2, triacylglycerol (TAG) content dramatically increased but glycerol and free fatty acid (FFA) significantly decreased, which implicated that NlCREB3-2 was involved in the lipase-related TAG metabolism. In N. lugens, five neutral lipases with complete features for TAG hydrolytic activity and high expression in ovary were focused. Among them, the expression levels of three neutral lipase genes were significantly down-regulated by NlCREB3-2 RNAi. The direct regulation of NlCREB3-2 towards the three neutral lipase genes was evidenced by the dual-luciferase reporter assay. After jointly silencing three neutral lipase genes, TAG and glycerol contents displayed similar changes as NlCREB3-2 RNAi. The study proved that NlCREB3-2 participated in TAG metabolism in ovary via the direct activation towards the ovary-specific neutral lipase genes.

Effects of kosmotropic, chaotropic, and neutral salts on Candida antarctica B lipase: An analysis of the secondary structure and its hydrolytic activity on triglycerides

The effects of different concentrations of Hofmeister salts on the hydrolytic activity on triglycerides and the secondary structure of lipase B from Candida antarctica (CALB) were investigated. Structural changes after short- and long-time incubation at high salt concentrations were determined using circular dichroism (CD), fluorescence, and RMSD-RMSF simulations. At 5.2 M NaCl, the hydrolytic activity of CALB on tributyrin (TC4) and trioctanoin (TC8) was enhanced by 1.5 (from 817 ± 3.9 to 1228 ± 4.3 U/mg)- and 8.7 (from 25 ± 0.3 to 218 ± 2.3 U/mg)-folds compared with 0.15 M NaCl, respectively at pH 7.0 and 40 °C. An activity activation was seen with other salts tested; however, long-time incubation (24 h) did not result in retention of the activation effect for any of the salts tested. Secondary structure CD and fluorescence spectra showed that long-time incubation with NaCl, KCl, and CsCl provokes a compact structure without loss of native conformation, whereas chaotropic LiCl and CaCl2 induced an increase in the α-helical content, and kosmotropic Na2SO4 provoked a molten globule state with rich β-sheet content. The RMSD-RMSF simulation agreed with the CD analysis, highlighting a principal salt-induced effect at the α-helix 5 region, promoting two different conformational states (open and closed) depending on the type and concentration of salt. Lastly, an increase in the interfacial tension occurred when high salt concentrations were added to the reaction media, affecting the catalytic properties. The results indicate that high-salt environments, such as 2-5.2 M NaCl, can be used to increase the lipolytic activity of CALB on TC4 and TC8.

Transcriptomic analysis of Mythimna separata ovaries and identification of genes involved in reproduction

The migratory insect Mythimna separata is a major pest of grain crops in Asia. Unfortunately, the molecular mechanisms that control and regulate reproduction in this species remain unclear. In this study, transcriptome sequencing was utilized to identify genes associated with ovary development and oogenesis. Clean sequences totaling 117.71 Gb were assembled into 178,534 unigenes with a mean length of 647.37 bp and N50 length of 837 bp. Transcriptome analysis showed that 7921 unigenes were significantly expressed in ovaries with 4403 and 3518 unigenes up- and down-regulated, respectively. Enrichment analysis with the Kyoto Encyclopedia of Genes and Genomes database suggested that 729 differentially expressed genes were significantly enriched in the top 20 pathways (q-values <0.05). Twenty genes were associated with ovary development and oogenesis and included lipases, Nanos, small heat shock proteins (sHsps) and histones; these were further verified by qRT-PCR and may play essential roles in M. separata reproduction. Collectively, our findings reveal underlying mechanisms of M.separata reproduction and may lead to RNAi-based management strategies targeting reproductive physiology.

Production of 4-Ethyl Malate through Position-Specific Hydrolysis of Photobacterium lipolyticum M37 Lipase

Microbial lipases are used widely in the synthesis of various compounds due to their substrate specificity and position specificity. 4-Ethyl malate (4-EM) made from diethyl malate (DEM) is an important starting material used to make argon fluoride (ArF) photoresist. We tested several microbial lipases and found that Photobacterium lipolyticum M37 lipase position-specifically hydrolyzed DEM to produce 4-EM. We purified the reaction product through silica gel chromatography and confirmed that it was 4-EM through nuclear magnetic resonance analysis. To mass-produce 4-EM, DEM hydrolysis reaction was performed using an enzyme reactor system that could automatically control the temperature and pH. Effects of temperature and pH on the reaction process were investigated. As a result, 50°C and pH 4.0 were confirmed as optimal reaction conditions, meaning that M37 was specifically an acid lipase. When the substrate concentration was increased to 6% corresponding to 0.32 M, the reaction yield reached almost 100%. When the substrate concentration was further increased to 12%, the reaction yield was 81%. This enzyme reactor system and position-specific M37 lipase can be used to mass-produce 4-EM, which is required to synthesize ArF photoresist.

Genome-Wide Identification and Analysis of Lipases in Fig Wasps (Chalcidoidea, Hymenoptera)

Simple Summary

Lipases are a large family of enzymes involved in lipid metabolism. Lipids play diverse roles in insect growth and responses to environmental stimuli. Fig wasps are a polyphyletic assemblage of Chalcidoidea that develop in the inflorescences of fig trees. Based on whether they can pollinate, they are separated into pollinator fig wasp (PFW) and non-pollinating fig wasp (NPFW). In this study, we conducted a genome-wide screening of lipases in the 12 fig wasp genomes using bioinformatics tools, including seven PFWs and five NPFWs. In total, 481 lipase genes were identified with the neutral and acid lipases as the most numerous families. NPFWs had significantly more lipases than PFWs. Tandem duplication accounted for the expansion of the gene family. Phylogenetic analysis indicated that the lipase genes were conserved. This study provided evidence of insect metabolism to understand the obligate mutualism between figs and fig wasps. Our results will facilitate the understanding of the molecular mechanism of how lipase proteins contribute to the distinctions of life histories between PFWs and NPFWs.

Abstract

Lipases are the main enzymes involved in lipid metabolism. However, the characteristics of lipases in insects were scarcely investigated. Here, we screened the recently sequenced genomes of 12 fig wasp species consisting of seven pollinator fig wasps (PFWs) and five non-pollinating fig wasps (NPFWs) for the six major lipase gene families. In total, 481 lipase genes were identified, and the two most numerous families were the neutral and acid lipases. Tandem duplication accounted for the expansion of the gene family. NPFWs had significantly more lipases than PFWs. A significant gene family contraction occurred in the clade of PFWs. The difference of lipases between NPFWs and PFWs might contribute to their distinction in life histories and feeding regimes. Phylogenetic analysis showed that the lipase genes of each fig wasp species was almost equally distributed in each clade, indicating that the lipase genes were conserved. The gene structures were similar within each clade, while they were different among clades. Most of the neutral and acid lipases were signal peptides and located extracellularly. The pathways of lipases involved were predicted. This genome-wide study provides a systematic analysis of lipase gene families in 12 hymenopteran insects and further insights towards understanding the potential functions of lipases.

Improved catalytic performance of carrier-free immobilized lipase by advanced cross-linked enzyme aggregates technology

The cross-linked enzyme aggregates (CLEAs) are one of the technologies that quickly immobilize the enzyme without a carrier. In this study, ionic liquid with amino group (1-aminopropyl-3-methylimidazole bromide, FIL) was used as the novel functional surface molecule to modify CRL (Candida rugosa lipase, CRL). The enzymatic properties of CRL-FIL-CLEAs were investigated. The activity of CRL-FIL-CLEAs (5.51 U/mg protein) was 1.9 times higher than that of CRL-CLEAs (2.86 U/mg protein) without surface modification. After incubating in a centrifuge tube for 50 min at 60 °C, CRL-FIL-CLEAs still maintained 61% of its initial activity, while the value for CRL-CLEAs was only 22%. After repeated use for five times, compared with the 22% residual activity of CRL-CLEAs, the value of CRL-FIL-CLEAs was 51%. Based on the above results, it was indicated that this method provided a new idea for the effective synthesis of immobilized enzyme.

Orientational Switch of the Lipase A Enzyme at the Oil-Water Interface: An Order of Magnitude Increase in Turnover Rate with a Single Surfactant Tag Explained

Interfacially active lipases can be immobilized at a biphasic interface to enhance turnover recyclability and to facilitate product separation. Extensive coarse-grained molecular dynamics simulations of lipase A (LipA) from Bacillus subtilis show a bimodal orientational distribution of the enzyme at an oil-water interface, arising from its ellipsoidal Janus particle-like character. The relative orientational preference can be tuned by pH. The simulations rationalize a rare experimental observation of an order of magnitude increase in the turnover rate of this lipase upon its noncovalent tagging by a single surfactant molecule at the interface, compared to its rate in bulk water. The adsorption free energy, the interfacial activation, a decrease in the number of orientational fluctuations, and an increased rate of translational diffusion, to all of which the Janus character of LipA contributes, are the factors responsible for this enhancement. This study can spur further investigations of the Janus behavior of enzymes to enhance their activity as well as to stabilize the biphasic emulsion needed for interfacial catalysis.

Insight into the Functional Diversification of Lipases in the Endoparasitoid Pteromalus puparum (Hymenoptera: Pteromalidae) by Genome-scale Annotation and Expression Analysis

Lipases play essential roles in digestion, transport, and processing of dietary lipids in insects. For parasitoid wasps with a unique life cycle, lipase functions could be multitudinous in particular. Pteromalus puparum is a pupal endoparasitoid of butterflies. The female adult deposits eggs into its host, along with multifunctional venom, and the developing larvae consume host as its main nutrition source. Parasitoid lipases are known to participate in the food digestion process, but the mechanism remains unclear. P. puparum genome and transcriptome data were interrogated. Multiple alignments and phylogenetic trees were constructed. We annotated a total of 64 predicted lipase genes belonging to five lipase families and suggested that eight venom and four salivary lipases could determine host nutrition environment post-parasitization. Many putative venom lipases were found with incomplete catalytic triads, relatively long β9 loops, and short lids. Data analysis reveals the loss of catalytic activities and weak triacylglycerol (TAG) hydrolytic activities of lipases in venom. Phylogenetic trees indicate various predicted functions of lipases in P. puparum. Our information enriches the database of parasitoid lipases and the knowledge of their functional diversification, providing novel insight into how parasitoid wasps manipulate host lipid storage by using venom lipases.

Production of trans-free interesterified fat using indigenously immobilized lipase

Enzymatic interesterification was carried out between high-oleic canola oil and fully hydrogenated soybean oil using indigenously immobilized Thermomyces lanuginosus lipas substrate concentration, moisture content of enzyme, and enzyme load. Interesterification resulted in a decrease in the concentration of tri-unsaturated and trisaturated TAG and an increase of mono- and di-saturated TAG as observed by reversed-phase HPLC. The alteration in TAG composition and the presence of new TAG species after interesterification was correlated with extended plasticity characterized by lower slip melting point with a significant change in functionality and consistency of the interesterified product. Thermal and structural properties of the blends before and after interesterification were assessed by differential scanning calorimetry (DSC), X-ray diffraction and polarized light microscopy. Trans-fat analysis indicated the absence of any trans fatty acid in the final interesterified product. The resultant interesterified products with varying slip melting points can be used in the formulation of healthier fat and oil products and address a critical industrial demand for trans free formulations for base-stocks of spreads, margarines, and confectionary fats.

Enzymatic Synthesis of Glycerol Carbonate Using a Lipase Immobilized on Magnetic Organosilica Nanoflowers as a Catalyst

For synthesizing glycerol carbonate (GC) by a reaction between glycerol (GL) and dimethyl carbonate (DMC), a lipase immobilized on magnetic organosilica nanoflowers was prepared and utilized as a biocatalyst. Candida antarctica lipase B (CALB) was chosen as a model enzyme for preparing an immobilized biocatalyst (CALB@nanoflowers). The obtained CALB@nanoflowers was characterized using scanning electron microscopy, transmission electron microscopy, and confocal laser scanning microscopy. Effects of GL/DMC molar ratio, biocatalyst amount, temperature, surfactant and molecular sieve addition, and reaction time on the conversion of GL and the selectivity of CALB@nanoflowers were investigated. The optimal catalytic performance (yield of GC: 88.66% and conversion of GL: 94.24%) was achieved under the condition of 1:20 molar ratio of GL to DMC with 0.2 g of molecular sieves added at 50 °C for 24 h. After recycling seven times, the CALB@nanoflowers maintained over 79% of its initial activity and the yield of GC was 70.31%.

pH-Induced Rotation of Lidless Lipase LipA from Bacillus subtilis at Lipase-Detergent Interface

Lipases exhibit a unique process during the catalysis of the hydrolysis of triglyceride substrates called interfacial activation. Surfactants are used as cosolvents with water not only to offer a less polar environment to the lipases needed for their interfacial activation but also to solvate the substrate which are poorly soluble in water. However, the presence of detergent in the medium can affect both the lipase and the substrate, making the construction of a microkinetic model for lipase activity in the presence of the detergent difficult. Herein, we study the interfacial activation of a lidless lipase LipA from Bacillus subtilis using extensive atomistic molecular dynamics simulations at different concentrations of the surfactant, Thesit (C12E8), at two pH values. Residues which bind to the monomeric detergent are found to be the same as the ones which have been reported earlier to bind to the substrate. Very importantly, a pH-induced rotation of the enzyme with respect to surfactant aggregate has been observed which not only explains the experimentally observed pH-dependent enzymatic activity of this lidless lipase, but also suggests its reorientation at an aqueous-lipodophilic interface.

Lipid metabolism in Rhodnius prolixus: Lessons from the genome

The kissing bug Rhodnius prolixus is both an important vector of Chagas' disease and an interesting model for investigation into the field of physiology, including lipid metabolism. The publication of this insect genome will bring a huge amount of new molecular biology data to be used in future experiments. Although this work represents a promising scenario, a preliminary analysis of the sequence data is necessary to identify and annotate the genes involved in lipid metabolism. Here, we used bioinformatics tools and gene expression analysis to explore genes from different genes families and pathways, including genes for fat breakdown, as lipases and phospholipases, and enzymes from β-oxidation, fatty acid metabolism, and acyl-CoA and glycerolipid synthesis. The R. prolixus genome encodes 31 putative lipase genes, including 21 neutral lipases and 5 acid lipases. The expression profiles of some of these genes were analyzed. We were able to identify nine phospholipase A2 genes. A variety of gene families that participate in fatty acid synthesis and modification were studied, including fatty acid synthase, elongase, desaturase and reductase. Concerning the synthesis of glycerolipids, we found a second isoform of glycerol-3-phosphate acyltransferase that was ubiquitously expressed throughout the organs. Finally, all genes involved in fatty acid β-oxidation were identified, but not a long-chain acyl-CoA dehydrogenase. These results provide fundamental data to be used in future research on insect lipid metabolism and its possible relevance to Chagas' disease transmission.

Efficient heterologous expression of Fusarium solani lipase, FSL2, in Pichia pastoris, functional characterization of the recombinant enzyme and molecular modeling

The gene coding for a lipase of Fusarium solani, designated as FSL2, shows an open reading frame of 906bp encoding a 301-amino acid polypeptide with a molecular mass of 30kDa. Based on sequence similarity with other fungal lipases, FSL2 contains a catalytic triad, consisting of Ser144, Asp198, and His256. FSL2 cDNA was subcloned into the pGAPZαA vector containing the Saccharomyces cerevisiae α-factor signal sequence and this construct was used to transform Pichia pastoris and achieve a high-level extracellular production of a FSL2 lipase. Maximum lipase activity was observed after 48h. The optimum activity of the purified recombinant enzyme was measured at pH 8.0-9.0 and 37°C. FSL2 is remarkably stable at alkaline pH values up to 12 and at temperatures below 40°C. It has high catalytic efficiency towards triglycerides with short to long chain fatty acids but with a marked preference for medium and long chain fatty acids. FSL2 activity is decreased at sodium taurodeoxycholate concentrations above the Critical Micelle Concentration (CMC) of this anionic detergent. However, lipase activity is enhanced by Ca²⁺ and inhibited by EDTA or Cu²⁺ and partially by Mg²⁺ or K⁺. In silico docking of medium chain triglycerides, monogalctolipids (MGDG), digalactolipids (DGDG) and long chain phospholipids in the active site of FSL2 reveals structural solutions.

Lipases That Activate at High Solvent Polarities

Thermomyces lanuginosus lipase (TlL) and related lipases become activated in low-polarity environments that exist at the water-lipid interface where a structural change of the "lid" region occurs. In this work, we have investigated the activation of TlL (Lipase_W89) and certain lid mutants, containing either a single positive charge mutation, E87K (Lipase_K87_W89), within the lid region or a lid residue composition of both lipase and esterase character (Hybrid_W89) as a function of solvent polarity. Activation differences between the variants and TlL were studied by a combination of biophysical and theoretical methods. To investigate the structural changes taking place in the lid region upon lipase activation, we used a fluorescence-based method measuring the efficiency of Trp89 in the lid to quench the fluorescence of a bimane molecule attached in front (C255) and behind (C61) the lid. These structural changes were compared to the enzymatic activity of each variant at the water-substrate interface and to theoretical calculations of the energies associated with lid opening as a function of the dielectric constant (ε) of the environment. Our results show that the lid in Lipase_K87_W89 undergoes a pronounced structural transition toward an open conformation around ε = 50, whereas only small changes are detected for Lipase_W89 ascribed to the stabilizing effect of the positive charge mutation on the open lid conformation. Interestingly, Hybrid_W89, with the same charge as Lipase_W89, shows a stabilization of the open lid even more pronounced at high solvent polarities than that of Lipase_K87_W89, allowing activation at ε < 80. This is further indicated by measurement of the lipase activity for each variant showing that Hybrid_W89 is more quickly activated at the water-lipid interface of a true, natural substrate. Combined, we show that a correlation exists between structural changes and enzymatic activities detected on one hand and theoretical calculations on lid opening energies on the other. These results highlight the key role that the lid plays in determining the polarity-dependent activation of lipases.

Functional dichotomy in the 16S rRNA (m1A1408) methyltransferase family and control of catalytic activity via a novel tryptophan mediated loop reorganization

Methylation of the bacterial small ribosomal subunit (16S) rRNA on the N1 position of A1408 confers exceptionally high-level resistance to a broad spectrum of aminoglycoside antibiotics. Here, we present a detailed structural and functional analysis of the Catenulisporales acidiphilia 16S rRNA (m¹A1408) methyltransferase (‘CacKam’). The apo CacKam structure closely resembles other m¹A1408 methyltransferases within its conserved SAM-binding fold but the region linking core β strands 6 and 7 (the ‘β6/7 linker’) has a unique, extended structure that partially occludes the putative 16S rRNA binding surface, and sequesters the conserved and functionally critical W203 outside of the CacKam active site. Substitution of conserved residues in the SAM binding pocket reveals a functional dichotomy in the 16S rRNA (m¹A1408) methyltransferase family, with two apparently distinct molecular mechanisms coupling cosubstrate/ substrate binding to catalytic activity. Our results additionally suggest that CacKam exploits the W203-mediated remodeling of the β6/7 linker as a novel mechanism to control 30S substrate recognition and enzymatic turnover.

Marine invertebrate lipases: Comparative and functional genomic analysis

Lipases are key enzymes involved in lipid digestion, storage and mobilization of reserves during fasting or heightened metabolic demand. This is a highly conserved process, essential for survival. The genomes of five marine invertebrate species with distinctive digestive system were screened for the six major lipase families. The two most common families in marine invertebrates, the neutral an acid lipases, are also the main families in mammals and insects. The number of lipases varies two-fold across analyzed genomes. A high degree of orthology with mammalian lipases was observed. Interestingly, 19% of the marine invertebrate lipases have lost motifs required for catalysis. Analysis of the lid and loop regions of the neutral lipases suggests that many marine invertebrates have a functional triacylglycerol hydrolytic activity as well as some acid lipases. A revision of the expression profiles and functional activity on sequences in databases and scientific literature provided information regarding the function of these families of enzymes in marine invertebrates.

Tuning the catalytic properties of lipases immobilized on divinylsulfone activated agarose by altering its nanoenvironment

Lipase from Thermomyces lanuginosus (TLL) and lipase B from Candida antarctica (CALB) have been immobilized on divinylsulfone (DVS) activated agarose beads at pH 10 for 72 h. Then, as a reaction end point, very different nucleophiles have been used to block the support and the effect of the nature of the blocking reagent has been analyzed on the features of the immobilized preparations. The blocking has generally positive effects on enzyme stability in both thermal and organic solvent inactivations. For example, CALB improved 7.5-fold the thermal stability after blocking with imidazole. The effect on enzyme activity was more variable, strongly depending on the substrate and the experimental conditions. Referring to CALB; using p-nitrophenyl butyrate (p-NPB) and methyl phenylacetate, activity always improved by the blocking step, whatever the blocking reagent, while with methyl mandelate or ethyl hexanoate not always the blocking presented a positive effect. Other example is TLL-DVS biocatalyst blocked with Cys. This was more than 8 times more active than the non-blocked preparation and become the most active versus p-NPB at pH 7, the least active versus methyl phenylacetate at pH 5 but the third one most active at pH 9, versus methyl mandelate presented lower activity than the unblocked preparation at pH 5 and versus ethyl hexanoate was the most active at all pH values. That way, enzyme specificity could be strongly altered by this blocking step.

LRAT-specific domain facilitates vitamin A metabolism by domain swapping in HRASLS3

Cellular uptake of vitamin A, production of visual chromophore and triglyceride homeostasis in adipocytes depend on two representatives of the vertebrate N1pC/P60 protein family, lecithin:retinol acyltransferase (LRAT) and HRAS-like tumor suppressor 3 (HRASLS3). Both proteins function as lipid-metabolizing enzymes but differ in their substrate preferences and dominant catalytic activity. The mechanism of this catalytic diversity is not understood. Here, by using a gain-of-function approach, we identified a specific sequence responsible for the substrate specificity of N1pC/P60 proteins. A 2.2-Å crystal structure of the HRASLS3-LRAT chimeric enzyme in a thioester catalytic intermediate state revealed a major structural rearrangement accompanied by three-dimensional domain swapping dimerization not observed in native HRASLS proteins. Structural changes affecting the active site environment contributed to slower hydrolysis of the catalytic intermediate, supporting efficient acyl transfer. These findings reveal structural adaptation that facilitates selective catalysis and mechanism responsible for diverse substrate specificity within the LRAT-like enzyme family.

Phosphatidic acid phospholipase A1 mediates ER-Golgi transit of a family of G protein-coupled receptors

Cytosolic phosphatidic acid phospholipase A1 interacts with COPII protein family members and is required for the anterograde trafficking of GPCRs.

The coat protein II (COPII)–coated vesicular system transports newly synthesized secretory and membrane proteins from the endoplasmic reticulum (ER) to the Golgi complex. Recruitment of cargo into COPII vesicles requires an interaction of COPII proteins either with the cargo molecules directly or with cargo receptors for anterograde trafficking. We show that cytosolic phosphatidic acid phospholipase A1 (PAPLA1) interacts with COPII protein family members and is required for the transport of Rh1 (rhodopsin 1), an N-glycosylated G protein–coupled receptor (GPCR), from the ER to the Golgi complex. In papla1 mutants, in the absence of transport to the Golgi, Rh1 is aberrantly glycosylated and is mislocalized. These defects lead to decreased levels of the protein and decreased sensitivity of the photoreceptors to light. Several GPCRs, including other rhodopsins and Bride of sevenless, are similarly affected. Our findings show that a cytosolic protein is necessary for transit of selective transmembrane receptor cargo by the COPII coat for anterograde trafficking.

Lipases in polymer chemistry

Lipases are highly active in the polymerization of a range of monomers. Both ring-opening polymerization of cyclic monomers such as lactones and carbonates as well as polycondensation reactions have been investigated in great detail. Moreover, in combination with other (chemical) polymerization techniques, lipase-catalyzed polymerization has been employed to synthesize a variety of polymer materials. Major advantages of enzymatic catalysts are the often-observed excellent regio-, chemo- and enantioselectivity that allows for the direct preparation of functional materials. In particular, the application of techniques such as Dynamic Kinetic Resolution (DKR) in the lipase-catalyzed polymerization of racemic monomers is a new development in enzymatic polymerization. This paper reviews selected examples of the application of lipases in polymer chemistry covering the synthesis of linear polymers, chemoenzymatic polymerization and applications of enantioselective techniques for the synthesis and modification of polymers.

TGL-mediated lipolysis in Manduca sexta fat body: possible roles for lipoamide-dehydrogenase (LipDH) and high-density lipophorin (HDLp)

Triglyceride-lipase (TGL) is a major fat body lipase in Manduca sexta. The knowledge of how TGL activity is regulated is very limited. A WWE domain, presumably involved in protein-protein interactions, has been previously identified in the N-terminal region of TGL. In this study, we searched for proteins partners that interact with the N-terminal region of TGL. Thirteen proteins were identified by mass spectrometry, and the interaction with four of these proteins was confirmed by immunoblot. The oxidoreductase lipoamide-dehydrogenase (LipDH) and the apolipoprotein components of the lipid transporter, HDLp, were among these proteins. LipDH is the common component of the mitochondrial α-keto acid dehydrogenase complexes whereas HDLp occurs in the hemolymph. However, subcellular fractionation demonstrated that these two proteins are relatively abundant in the soluble fraction of fat body adipocytes. The cofactor lipoate found in typical LipDH substrates was not detected in TGL. However, TGL proved to have critical thiol groups. Additional studies with inhibitors are consistent with the notion that LipDH acting as a diaphorase could preserve the activity of TGL by controlling the redox state of thiol groups. On the other hand, when TG hydrolase activity of TGL was assayed in the presence of HDLp, the production of diacylglycerol (DG) increased. TGL-HDLp interaction could drive the intracellular transport of DG. TGL may be directly involved in the lipoprotein assembly and loading with DG, a process that occurs in the fat body and is essential for insects to mobilize fatty acids. Overall the study suggests that TGL occurs as a multi-protein complex supported by interactions through the WWE domain.

Integrative study of physiological changes associated with bacterial infection in Pacific oyster larvae

Background

Bacterial infections are common in bivalve larvae and can lead to significant mortality, notably in hatcheries. Numerous studies have identified the pathogenic bacteria involved in such mortalities, but physiological changes associated with pathogen exposure at larval stage are still poorly understood. In the present study, we used an integrative approach including physiological, enzymatic, biochemical, and molecular analyses to investigate changes in energy metabolism, lipid remodelling, cellular stress, and immune status of Crassostrea gigas larvae subjected to experimental infection with the pathogenic bacteria Vibrio coralliilyticus.

Findings

Our results showed that V. coralliilyticus exposure induced (1) limited but significant increase of larvae mortality compared with controls, (2) declined feeding activity, which resulted in energy status changes (i.e. reserve consumption, β-oxidation, decline of metabolic rate), (3) fatty acid remodeling of polar lipids (changes in phosphatidylinositol and lysophosphatidylcholine composition`, non-methylene–interrupted fatty acids accumulation, lower content of major C₂₀ polyunsaturated fatty acids as well as activation of desaturases, phospholipase and lipoxygenase), (4) activation of antioxidant defenses (catalase, superoxide dismutase, peroxiredoxin) and cytoprotective processes (heat shock protein 70, pernin), and (5) activation of the immune response (non-self recognition, NF-κκ signaling pathway, haematopoiesis, eiconosoids and lysophosphatidyl acid synthesis, inhibitor of metalloproteinase and antimicrobial peptides).

Conclusion

Overall, our results allowed us to propose an integrative view of changes induced by a bacterial infection in Pacific oyster larvae, opening new perspectives on the response of marine bivalve larvae to infections.

Unlocking the mystery behind the activation phenomenon of T1 lipase: a molecular dynamics simulations approach

The activation of lipases has been postulated to proceed by interfacial activation, temperature switch activation, or aqueous activation. Recently, based on molecular dynamics (MD) simulation experiments, the T1 lipase activation mechanism was proposed to involve aqueous activation in addition to a double-flap mechanism. Because the open conformation structure is still unavailable, it is difficult to validate the proposed theory unambiguously to understand the behavior of the enzyme. In this study, we try to validate the previous reports and uncover the mystery behind the activation process using structural analysis and MD simulations. To investigate the effects of temperature and environmental conditions on the activation process, MD simulations in different solvent environments (water and water-octane interface) and temperatures (20, 50, 70, 80, and 100°C) were performed. Based on the structural analysis of the lipases in the same family of T1 lipase (I.5 lipase family), we proposed that the lid domain comprises α6 and α7 helices connected by a loop, thus forming a helix-loop-helix motif involved in interfacial activation. Throughout the MD simulations experiments, lid displacements were only observed in the water-octane interface, not in the aqueous environment with respect to the temperature effect, suggesting that the activation process is governed by interfacial activation coupled with temperature switch activation. Examining the activation process in detail revealed that the large structural rearrangement of the lid domain was caused by the interaction between the hydrophobic residues of the lid with octane, a nonpolar solvent, and this conformation was found to be thermodynamically favorable.

Lipases as biocatalysts for the synthesis of structured lipids

Structured lipids (SL) are broadly referred to as modified or synthetic oils and fats or lipids with functional or pharmaceutical applications. Some structured lipids, such as triglycerides that contain both long-chain (mainly essential) fatty acids and medium- or short-chain fatty acids and also artificial products that mimic the structure of natural materials, namely human milk fat substitutes and cocoa butter equivalents, have been discussed. Further, other modified or synthetic lipids, such as structured phospholipids and synthetic phenolic lipids are also included in this chapter. For all the products described in this chapter, enzymatic production in industry has been already conducted in one way or another. Cocoa butter equivalents, healthy oil containing medium-chain fatty acids, phosphatidyl serine, and phenol lipids from enzyme technology have been reported for commercial operation. As the demand for better quality functional lipids is increasing, the production of structured lipids becomes an interesting area. Thus, in this chapter we have discussed latest developments as well as present industrial situation of all commercially important structured lipids.

Effect of fasting on digestive gland lipase transcripts expression in Penaeus vannamei

Digestive and intracellular lipases were studied in the digestive gland of whiteleg shrimp Penaeus vannamei. A partial sequence of the intracellular lipase was obtained from the digestive gland cDNA. The digestive and intracellular lipase mRNAs were detected differentially in different body parts of shrimp; digestive lipase mRNA is exclusively found in the digestive gland, suggesting a function as a digestive enzyme. Intracellular lipase mRNA was found in pleopods, digestive tube, uropods, hemocytes, muscle and gonad and its function was related to mobilization of energy reserves. The lipase transcripts in the digestive gland of shrimp, showed a dynamic expression at 120 h of fasting causing significant changes of digestive and intracellular mRNA, intracellular lipase mRNA were 3.33-fold higher than digestive lipase mRNA after fasting period, suggesting an alternate expression to maintain the lipid homeostasis under stress conditions.

Structural determinants of ligand imprinting: a molecular dynamics simulation study of subtilisin in aqueous and apolar solvents

The phenomenon known as "ligand imprinting" or "ligand-induced enzyme memory" was first reported in 1988, when Russell and Klibanov observed that lyophilizing subtilisin in the presence of competitive inhibitors (that were subsequently removed) could significantly enhance its activity in an apolar solvent. (Russell and Klibanov, J Biol Chem 1988;263:11624-11626). They further observed that this enhancement did not occur when similar assays were carried out in water. Herein, we shed light on the molecular determinants of ligand imprinting using a molecular dynamics (MD) approach. To simulate the effect of placing an enzyme in the presence of a ligand before its lyophilization, an inhibitor was docked in the active site of subtilisin and 20 ns MD simulations in water were performed. The ligand was then removed and the resulting structure was used for subsequent MD runs using hexane and water as solvents. As a control, the same simulation setup was applied using the structure of subtilisin in the absence of the inhibitor. We observed that the ligand maintains the active site in an open conformation and that this configuration is retained after the removal of the inhibitor, when the simulations are carried out in hexane. In agreement with experimental findings, the structural configuration induced by the ligand is lost when the simulations take place in water. Our analysis of fluctuations indicates that this behavior is a result of the decreased flexibility displayed by enzymes in an apolar solvent, relatively to the aqueous situation.

Exploring the conformational states and rearrangements of Yarrowia lipolytica Lipase

We report the 1.7 Å resolution crystal structure of the Lip2 lipase from Yarrowia lipolytica in its closed conformation. The Lip2 structure is highly homologous to known structures of the fungal lipase family (Thermomyces lanuginosa, Rhizopus niveus, and Rhizomucor miehei lipases). However, it also presents some unique features that are described and discussed here in detail. Structural differences, in particular in the conformation adopted by the so-called lid subdomain, suggest that the opening mechanism of Lip2 may differ from that of other fungal lipases. Because the catalytic activity of lipases is strongly dependent on structural rearrangement of this mobile subdomain, we focused on elucidating the molecular mechanism of lid motion. Using the x-ray structure of Lip2, we carried out extensive molecular-dynamics simulations in explicit solvent environments (water and water/octane interface) to characterize the major structural rearrangements that the lid undergoes under the influence of solvent or upon substrate binding. Overall, our results suggest a two-step opening mechanism that gives rise first to a semi-open conformation upon adsorption of the protein at the water/organic solvent interface, followed by a further opening of the lid upon substrate binding.

Comparative and functional genomics of lipases in holometabolous insects

Lipases have key roles in insect lipid acquisition, storage and mobilisation and are also fundamental to many physiological processes underpinning insect reproduction, development, defence from pathogens and oxidative stress, and pheromone signalling. We have screened the recently sequenced genomes of five species from four orders of holometabolous insects, the dipterans Drosophila melanogaster and Anopheles gambiae, the hymenopteran Apis mellifera, the moth Bombyx mori and the beetle Tribolium castaneum, for the six major lipase families that are also found in other organisms. The two most numerous families in the insects, the neutral and acid lipases, are also the main families in mammals, albeit not in Caenorhabditis elegans, plants or microbes. Total numbers of the lipases vary two-fold across the five insect species, from numbers similar to those in mammals up to numbers comparable to those seen in C. elegans. Whilst there is a high degree of orthology with mammalian lipases in the other four families, the great majority of the insect neutral and acid lipases have arisen since the insect orders themselves diverged. Intriguingly, about 10% of the insect neutral and acid lipases have lost motifs critical for catalytic function. Examination of the length of lid and loop regions of the neutral lipase sequences suggest that most of the insect lipases lack triacylglycerol (TAG) hydrolysis activity, although the acid lipases all have intact cap domains required for TAG hydrolysis. We have also reviewed the sequence databases and scientific literature for insights into the expression profiles and functions of the insect neutral and acid lipases and the orthologues of the mammalian adipose triglyceride lipase which has a pivotal role in lipid mobilisation. These data suggest that some of the acid and neutral lipase diversity may be due to a requirement for rapid accumulation of dietary lipids. The different roles required of lipases at the four discrete life stages of holometabolous insects may also contribute to the diversity of lipases required by insects. In addition, insects use lipases to perform roles for which there are no correlates in mammals, including as yolk and male accessory gland proteins.

Lipoprotein lipase: from gene to obesity

Lipoprotein lipase (LPL) is a multifunctional enzyme produced by many tissues, including adipose tissue, cardiac and skeletal muscle, islets, and macrophages. LPL is the rate-limiting enzyme for the hydrolysis of the triglyceride (TG) core of circulating TG-rich lipoproteins, chylomicrons, and very low-density lipoproteins (VLDL). LPL-catalyzed reaction products, fatty acids, and monoacylglycerol are in part taken up by the tissues locally and processed differentially; e.g., they are stored as neutral lipids in adipose tissue, oxidized, or stored in skeletal and cardiac muscle or as cholesteryl ester and TG in macrophages. LPL is regulated at transcriptional, posttranscriptional, and posttranslational levels in a tissue-specific manner. Nutrient states and hormonal levels all have divergent effects on the regulation of LPL, and a variety of proteins that interact with LPL to regulate its tissue-specific activity have also been identified. To examine this divergent regulation further, transgenic and knockout murine models of tissue-specific LPL expression have been developed. Mice with overexpression of LPL in skeletal muscle accumulate TG in muscle, develop insulin resistance, are protected from excessive weight gain, and increase their metabolic rate in the cold. Mice with LPL deletion in skeletal muscle have reduced TG accumulation and increased insulin action on glucose transport in muscle. Ultimately, this leads to increased lipid partitioning to other tissues, insulin resistance, and obesity. Mice with LPL deletion in the heart develop hypertriglyceridemia and cardiac dysfunction. The fact that the heart depends increasingly on glucose implies that free fatty acids are not a sufficient fuel for optimal cardiac function. Overall, LPL is a fascinating enzyme that contributes in a pronounced way to normal lipoprotein metabolism, tissue-specific substrate delivery and utilization, and the many aspects of obesity and other metabolic disorders that relate to energy balance, insulin action, and body weight regulation.

Modeling of solvent-dependent conformational transitions in Burkholderia cepacia lipase

BACKGROUND

The characteristic of most lipases is the interfacial activation at a lipid interface or in non-polar solvents. Interfacial activation is linked to a large conformational change of a lid, from a closed to an open conformation which makes the active site accessible for substrates. While for many lipases crystal structures of the closed and open conformation have been determined, the pathway of the conformational transition and possible bottlenecks are unknown. Therefore, molecular dynamics simulations of a closed homology model and an open crystal structure of Burkholderia cepacia lipase in water and toluene were performed to investigate the influence of solvents on structure, dynamics, and the conformational transition of the lid.

RESULTS

The conformational transition of B. cepacia lipase was dependent on the solvent. In simulations of closed B. cepacia lipase in water no conformational transition was observed, while in three independent simulations of the closed lipase in toluene the lid gradually opened during the first 10-15 ns. The pathway of conformational transition was accessible and a barrier was identified, where a helix prevented the lid from opening to the completely open conformation. The open structure in toluene was stabilized by the formation of hydrogen bonds.In simulations of open lipase in water, the lid closed slowly during 30 ns nearly reaching its position in the closed crystal structure, while a further lid opening compared to the crystal structure was observed in toluene. While the helical structure of the lid was intact during opening in toluene, it partially unfolded upon closing in water. The closing of the lid in water was also observed, when with eight intermediate structures between the closed and the open conformation as derived from the simulations in toluene were taken as starting structures. A hydrophobic beta-hairpin was moving away from the lid in all simulations in water, which was not observed in simulations in toluene. The conformational transition of the lid was not correlated to the motions of the beta-hairpin structure.

CONCLUSION

Conformational transitions between the experimentally observed closed and open conformation of the lid were observed by multiple molecular dynamics simulations of B. cepacia lipase. Transitions in both directions occurred without applying restraints or external forces. The opening and closing were driven by the solvent and independent of a bound substrate molecule.

Therapeutic potential of RNA interference against cellular targets of HIV infection

RNA interference is not only very promising in identifying new targets for drug development, siRNA/shRNA themselves may be directly used as therapeutic agents. In inhibiting viral infections by RNA interference, both viral targets and cellular proteins have been evaluated. Most of the early studies in this field had chosen viral targets for RNA interference. However, recent efforts are mainly focusing on cellular proteins for RNA silencing due to the realization that a variety of viral responses substantially minimize siRNA effects. With the application of siRNA approaching, many new cellular targets relevant to HIV infection have been identified. The value of siRNA/shRNA in the treatment of AIDS is largely dependent on better understanding of the biology of HIV replication. Efforts in the identification of cellular processes with the employment of siRNA/shRNA have shed some new lights on our understanding of how HIV infection occurs. Furthermore, the relative specific effects and simplicity of design makes siRNA/shRNA themselves to be favorable drug leads.

Effect of nonionic surfactants on Rhizopus homothallicus lipase activity

Based on amino-terminal sequencing and mass spectrometry data on the Rhizopus homothallicus lipase extracted using solid (SSF) and submerged state fermentation (SmF) methods, we previously established that the two enzymes were identical. Differences were observed, however, in terms of the specific activity of these lipases and their inhibition by diethyl p-nitrophenyl phosphate (E600). The specific activity of the SSF lipase (10,700 mumol/min/mg) was found to be 1.2-fold that of SmF lipase (8600 mumol/min/mg). These differences might be the result of residual Triton X-100 molecules interacting with the SSF lipase. To check this hypothesis, the SmF lipase was incubated with submicellar concentrations of Triton X-100. The specific activity of the lipase increased after this treatment, reaching similar values to those measured with the SSF lipase. Preincubating SSF and SmF lipases with E600 at a molar excess of 100 for 1 h resulted in 80% and 60% enzyme inhibition levels, respectively. When the SmF lipase was preincubated with Triton X-100 for 1 h at a concentration 100 times lower than the Triton X-100 critical micellar concentration, the inhibition of the lipase by E600 increased from 60% to 80%. These results suggest that residual detergent monomers interacting with the enzyme may affect the kinetic properties of the Rh. homothallicus lipase.