Cysteine residues in human lysosomal acid lipase are involved in selective cholesteryl esterase activity

In silico mining and identification of a novel lipase from Paenibacillus larvae: Rational protein design for improving catalytic performance

Lipases play a vital role in various biological processes, from lipid metabolism to industrial applications. However, the ever-evolving challenges and diverse substrates necessitate the continual exploration of novel high-performance lipases. In this study, we employed an in silico mining approach to search for lipases with potential high sn-1,3 selectivity and catalytic activity. The identified novel lipase, PLL, from Paenibacillus larvae subsp. larvae B-3650 exhibited a specific activity of 111.2 ± 5.5 U/mg towards the substrate p-nitrophenyl palmitate (pNPP) and 6.9 ± 0.8 U/mg towards the substrate olive oil when expressed in Escherichia coli (E. coli). Computational design of cysteine mutations was employed to enhance the catalytic performance of PLL. Superior stability was achieved with the mutant K7C/A386C/H159C/K108C (2M3/2M4), showing an increase in melting temperature (Tm) by 1.9°C, a 2.05-fold prolonged half-life at 45°C, and no decrease in enzyme activity. Another mutant, K7C/A386C/A174C/A243C (2M1/2M3), showed a 4.9-fold enhancement in specific activity without compromising stability. Molecular dynamics simulations were conducted to explore the mechanisms of these two mutants. Mutant 2M3/2M4 forms putative disulfide bonds in the loop region, connecting the N- and C-termini of PLL, thus enhancing overall structural rigidity without impacting catalytic activity. The cysteines introduced in mutant 2M1/2M3 not only form new intramolecular hydrogen bonds but also alter the polarity and volume of the substrate-binding pocket, facilitating the entry of large substrate pNPP. These results highlight an efficient in silico exploration approach for novel lipases, offering a rapid and efficient method for enhancing catalytic performance through rational protein design.

Crystal structure of human lysosomal acid lipase and its implications in cholesteryl ester storage disease

Lysosomal acid lipase (LAL) is a serine hydrolase that hydrolyzes cholesteryl ester (CE) and TGs delivered to the lysosomes into free cholesterol and fatty acids. LAL deficiency due to mutations in the LAL gene (LIPA) results in accumulation of TGs and cholesterol esters in various tissues of the body leading to pathological conditions such as Wolman's disease and CE storage disease (CESD). Here, we present the first crystal structure of recombinant human LAL (HLAL) to 2.6 Å resolution in its closed form. The crystal structure was enabled by mutating three of the six potential glycosylation sites. The overall structure of HLAL closely resembles that of the evolutionarily related human gastric lipase (HGL). It consists of a core domain belonging to the classical α/β hydrolase-fold family with a classical catalytic triad (Ser-153, His-353, Asp-324), an oxyanion hole, and a "cap" domain, which regulates substrate entry to the catalytic site. Most significant structural differences between HLAL and HGL exist at the lid region. Deletion of the short helix, 238NLCFLLC244, at the lid region implied a possible role in regulating the highly hydrophobic substrate binding site from self-oligomerization during interfacial activation. We also performed molecular dynamic simulations of dog gastric lipase (lid-open form) and HLAL to gain insights and speculated a possible role of the human mutant, H274Y, leading to CESD.

Cloning, phylogenetic analysis and 3D modeling of a putative lysosomal acid lipase from the camel, Camelus dromedarius

Acid lipase belongs to a family of enzymes that is mainly present in lysosomes of different organs and the stomach. It is characterized by its capacity to withstand acidic conditions while maintaining high lipolytic activity. We cloned for the first time the full coding sequence of camel’s lysosomal acid lipase, cLIPA using RT-PCR technique (Genbank accession numbers JF803951 and AEG75815, for the nucleotide and aminoacid sequences respectively). The cDNA sequencing revealed an open reading frame of 1,197 nucleotides that encodes a protein of 399 aminoacids which was similar to that from other related mammalian species. Bioinformatic analysis was used to determine the aminoacid sequence, 3D structure and phylogeny of cLIPA. Bioinformatics analysis suggested the molecular weight of the translated protein to be 45.57 kDa, which could be decreased to 43.16 kDa after the removal of a signal peptide comprising the first 21 aminoacids. The deduced cLIPA sequences exhibited high identity with Equus caballus (86%), Numascus leucogenys (85%), Homo sapiens (84%), Sus scrofa (84%), Bos taurus (82%) and Ovis aries (81%). cLIPA shows high aminoacid sequence identity with human and dog-gastric lipases (58%, and 59% respectively) which makes it relevant to build a 3D structure model for cLIPA. The comparison confirms the presence of the catalytic triad and the oxyanion hole in cLIPA. Phylogenetic analysis revealed that camel cLIPA is grouped with monkey, human, pig, cow and goat. The level of expression of cLIPA in five camel tissues was examined using Real Time-PCR. The highest level of cLIPA transcript was found in the camel testis (162%), followed by spleen (129%), liver (100%), kidney (20.5%) and lung (17.4%).

Atherosclerosis: a redox-sensitive lipid imbalance suppressible by cyclopentenone prostaglandins

Disorders concerning the metabolism of plasma and intracellular lipids are hallmarks of atherosclerosis. However, failures in proper control of intracellular cholesterol balance, rather than simple cholesterol overloading due to augmented uptake, could fuel atherogenesis. Therefore, the understanding of atherosclerosis-associated lipid alterations, which feed an inflammatory microenvironment in the arterial wall, requires the meticulous investigation of several aspects of lipid synthesis, uptake and export from cells. In this regard, the presence of reactive cysteines in transcription factors and key enzymes of lipid metabolism may dictate cholesterol accumulation, and therefore the progression of vascular disease. The strong inhibitory effect of cysteine-reactant anti-inflammatory cyclopentenone prostaglandins (CP-PGs) over atherosclerosis progression in vivo (LipoCardium technology) symbolizes a new concept of atherosclerosis and its treatment. Results from this laboratory and those from other research groups have unraveled a novel facet in prostaglandin research in that CP-PGs may act as redox signals that guide lipid metabolism in atherosclerosis. By modifying enzymes (e.g., HMG-CoA reductase, ACAT and cholesteryl ester hydrolases) and transcription factors (e.g., NF-kappaB and Keap1) involved in inflammation and lipid metabolism, CP-PGs (especially those of A-series) induce pivotal changes in glutathione and lipid metabolism that completely arrest atherosclerosis progression. Hence, pharmacological manipulation of lipid metabolism by CP-PGs may be a novel and invaluable strategy for treating atherosclerosis. Also, a better understanding of why CP-PGs do not resolve inflammation physiologically may explain many unsolved questions and yield insights into atherogenesis and its termination.

Purification, cloning and regulation of a novel acid-lipase-like protein of hamster expressed in lacrimal glands and tears during lactation

We report a novel 48-kDa tear acid-lipase-like protein (TALLP), which is markedly induced in lacrimal glands (LG) and secreted in tears of hamster dams during lactation. TALLP is undetectable in LG and tears of normal hamsters, but is also induced after gonadectomy in both sexes and this is prevented by androgen, estrogen or thyroid hormone treatment. These observations and the obliteration of TALLP upon cessation of lactation suggest that endogenous estrogens (in females) and androgens (in males) completely repress TALLP expression. Purified TALLP is monomeric, contains approximately 18% N-glycosylation and several pI isoforms. TALLP expression was tissue-specific and immunolocalized in LG acinar cells. The cDNA deduced amino-acid sequence of TALLP precursor (398 residue, containing a 19 residues signal-peptide) showed only 43-48% identity with all known mammalian acid-lipases, including even those of other rodents, suggesting that TALLP is a prototype of a new category, within the acid-lipase family. Surprisingly, although the catalytic triad residues and other sequence features important for lipolytic activity are conserved in TALLP, it has no detectable lipase activity. However, TALLP binds the polarity sensitive hydrophobic probe, 1-aminoanthracene (K(d)=12 microM). TALLP might have a unique substrate-specificity or a lipid-binding/carrier function in tears of hamster dams. This is the first report of an acid-lipase-like protein secreted in tears of any species. Since TALLP lacks the usual lipase activity, it can be an excellent model to understand better what other structural features in acid-lipases influence their catalytic activity.

The lipid droplet enzyme Tgl1p hydrolyzes both steryl esters and triglycerides in the yeast, Saccharomyces cerevisiae

Based on sequence homology to mammalian acid lipases, yeast reading frame YKL140w was predicted to encode a triacylglycerol (TAG) lipase in yeast and was hence named as TGL1, triglyceride lipase 1. A deletion of TGL1, however, resulted in an increase of the cellular steryl ester content. Fluorescently labeled lipid analogs that become covalently linked to the enzyme active site upon catalysis were used to discriminate between the lipase and esterase activities of Tgl1p. Tgl1p preferred single-chain esterase inhibitors over lipase inhibitors in vitro. Under assay conditions optimal for acid lipases, Tgl1p exhibited steryl esterase activity only and lacked any triglyceride lipase activity. In contrast, at pH 7.4, Tgl1p also exhibited TAG lipase activity; however, steryl ester hydrolase activity was still predominant. Tgl1p localized exclusively to lipid droplets which are the intracellular storage compartment of steryl esters and triacylglycerols in the yeast S. cerevisiae. In a tgl1 deletion mutant, the mobilization of steryl esters in vivo was delayed, but not abolished, suggesting the existence of additional enzymes involved in steryl ester mobilization.

The Saccharomyces cerevisiae YLL012/YEH1, YLR020/YEH2, and TGL1 genes encode a novel family of membrane-anchored lipases that are required for steryl ester hydrolysis

Sterol homeostasis in eukaryotic cells relies on the reciprocal interconversion of free sterols and steryl esters. The formation of steryl esters is well characterized, but the mechanisms that control steryl ester mobilization upon cellular demand are less well understood. We have identified a family of three lipases of Saccharomyces cerevisiae that are required for efficient steryl ester mobilization. These lipases, encoded by YLL012/YEH1, YLR020/YEH2, and TGL1, are paralogues of the mammalian acid lipase family, which is composed of the lysosomal acid lipase, the gastric lipase, and four novel as yet uncharacterized human open reading frames. Lipase triple-mutant yeast cells are completely blocked in steryl ester hydrolysis but do not affect the mobilization of triacylglycerols, indicating that the three lipases are required for steryl ester mobilization in vivo. Lipase single mutants mobilize steryl esters to various degrees, indicating partial functional redundancy of the three gene products. Lipase double-mutant cells in which the third lipase is expressed from the inducible GAL1 promoter have greatly reduced steady-state levels of steryl esters, indicating that overexpression of any of the three lipases is sufficient for steryl ester mobilization in vivo. The three yeast enzymes constitute a novel class of membrane-anchored lipases that differ in topology and subcellular localization.

Difference in substrate specificity between human and mouse lysosomal acid lipase: low affinity for cholesteryl ester in mouse lysosomal acid lipase

Lysosomal acid lipase (LAL) is essential for the intracellular degradation of cholesteryl esters (CE) and triacylglycerols (TG) that are delivered to lysosomes by low density lipoprotein (LDL) receptor mediated endocytosis. We have analysed the difference in the catalytic properties and substrate specificity of human and mouse LALs. LAL activities were measured in human and mouse fibroblasts and in HeLa cells transiently expressing wild-type or site-directed mutant LALs of the two species using the T7 vaccinia system. Cholesteryl esterase and triacylglycerol lipase activities were determined in cellular homogenates with a phospholipid/detergent vesicle assay, an assay frequently used to diagnose human LAL deficiency syndromes, and with LDL particles, a more physiological substrate. Characterisation of human and mouse LAL using these two assays demonstrated marked differences in their TG and CE hydrolysing activities. Compared to human LAL mouse LAL showed a much lower cholesteryl esterase activity in both assays used. The difference was more pronounced in the vesicle assay. The lower cholesteryl esterase activity of mouse LAL did not affect the LDL-CE degradation in intact fibroblasts. The analysis of site-directed mutants suggests a role of the non-conserved cysteine residue at position 240 in cholesteryl esterase activity in human LAL. Our results show a significant difference between human and mouse LAL in their specificity toward cholesteryl esters. The low cholesteryl esterase activity does not result in reduced LDL-cholesterol ester degradation in mouse fibroblasts in situ. In addition, this work emphasises the importance of the physical state of substrates in studies of the specificity and properties of lipolytic enzymes.

Molecular and enzymatic analyses of lysosomal acid lipase in cholesteryl ester storage disease

Human lysosomal acid lipase (hLAL) is essential for the hydrolysis of cholesteryl esters and triglycerides in the lysosome. Defective hLAL activity leads to two autosomal recessive traits, Wolman disease (WD) or cholesteryl ester storage disease (CESD). Phenotypically, WD has accumulation of both triglycerides and cholesteryl esters, while CESD has mainly elevated cholesteryl esters. We characterized mutations in the hLAL gene from two CESD siblings. By reverse transcriptase-PCR (RT-PCR) and cDNA cloning and sequencing, we identified homozygous deletion mutations of nucleotides 863 to 934, in the hLAL transcript. Normal levels of LAL mRNA were detected. The deletion in mRNA is due to a G to A transition in the last nucleotide of exon 8 of the hLAL gene, a splice junction mutation (E8SJM) that resulted in exon skipping, and a predicted in-frame deletion of the 24 amino acids. [35S]Met metabolic labeling studies in fibroblasts showed a low level of E8SJM LAL ( approximately 38%) that was highly unstable. Heterologous expression of E8SJM LAL in insect cells gave an LAL with low catalytic activity toward cholesteryl oleate and triolein. The effects of this mutation are complex with the production of decreased amounts of an unstable LAL that is catalytically defective. The results suggest that E8SJM leads to essentially a null allele and that the differences in WD and CESD phenotype involve other factors.