Mass spectrometric evidence of covalently-bound tetrahydrolipstatin at the catalytic serine of Streptomyces rimosus lipase

Pseudomonas aeruginosaesterase PA2949, a bacterial homolog of the human membrane esterase ABHD6: expression, purification and crystallization

Homologous expression of the membrane-bound esterase PA2949 from Pseudomonas aeruginosa PA01 and the purification of detergent-solubilized enzyme resulted in stable PA2949 protein that crystallized. The crystals obtained were used for X-ray analysis and diffracted to a resolution of 2.74 Å.

The human membrane-bound α/β-hydrolase domain 6 (ABHD6) protein modulates endocannabinoid signaling, which controls appetite, pain and learning, as well as being linked to Alzheimer’s and Parkinson’s diseases, through the degradation of the key lipid messenger 2-arachidonylglycerol (2-AG). This makes ABHD6 an attractive therapeutic target that lacks structural information. In order to better understand the molecular mechanism of 2-AG-hydrolyzing enzymes, the PA2949 protein from Pseudomonas aeruginosa, which has 49% sequence similarity to the ABHD6 protein, was cloned, overexpressed, purified and crystallized. Overexpression of PA2949 in the homologous host yielded the membrane-bound enzyme, which was purified in milligram amounts. Besides their sequence similarity, the enzymes both show specificity for the hydrolysis of 2-AG and esters of medium-length fatty acids. PA2949 in the presence of n-octyl β-d-glucoside showed a higher activity and stability at room temperature than those previously reported for PA2949 overexpressed and purified from Escherichia coli. A suitable expression host and stabilizing detergent were crucial for obtaining crystals, which belonged to the tetragonal space group I4₁22 and diffracted to a resolution of 2.54 Å. This study provides hints on the functional similarity of ABHD6-like proteins in prokaryotes and eukaryotes, and might guide the structural study of these difficult-to-crystallize proteins.

A membrane-bound esterase PA2949 from Pseudomonas aeruginosa is expressed and purified from Escherichia coli

Pseudomonas aeruginosa strain 1001 produces an esterase (EstA) that can hydrolyse the racemic methyl ester of β-acetylthioisobutyrate to produce the (D)-enantiomer, which serves as a precursor of captopril, a drug used for treatment of hypertension. We show here that PA2949 from P. aeruginosa PA01, a homologue of EstA, can efficiently be expressed in an enzymatically active form in E. coli. The enzyme is membrane-associated as demonstrated by cell fractionation studies. PA2949 was purified to homogeneity after solubilisation with the nonionic detergent, Triton X-100, and was shown to possess a conserved esterase catalytic triad consisting of Ser137-His258-Asp286. Our results should allow the development of an expression and purification strategy to produce this biotechnologically relevant esterase in a pure form with a high yield.

The effects of the broad-specificity lipase inhibitor, tetrahydrolipstatin, on the growth, development and survival of the larvae of Epiphyas postvittana (Walker) (Tortricidae, Lepidoptera)

The effects of the lipase inhibitor, tetrahydrolipstatin (THL), on neonate Epiphyas postvittana (Walker) (Lepidoptera, Tortricidae) larvae were investigated by feeding on control artificial diets (with and without 2% ethanol) and diets containing 2% ethanol and one of three concentrations of THL (0.011%, 0.037% and 0.11%). Small but significant reductions in growth rate, percent pupation and time to pupation were observed for larvae feeding on 2% ethanol control diet compared with standard control diet, but larger reductions in all parameters occurred with increasing THL concentration. Third instar larvae fed 0.011% THL in the diet had 40% of the midgut lipase activity in the relevant control larvae and showed up-regulation of gene expression of the gastric lipase-like family but not the pancreatic lipase-like family of midgut lipases.

Lipase inhibitor orlistat decreases incorporation of eicosapentaenoic and docosahexaenoic acids in rat tissues

Orlistat is a gastric and pancreatic lipases inhibitor that is often prescribed to obese subjects. Orlistat has been shown to decrease the absorption of biologically important lipophilic micronutrients such as liposoluble vitamins. We hypothesized that long-term administration of orlistat may lower the incorporation of n-3 long-chain polyunsaturated fatty acids (LC-PUFA) in blood lipids and tissues. This hypothesis was tested in rats fed a diet supplemented with fish oil as a source of n-3 LC-PUFA. Male Wistar rats (n = 18) were divided into 3 groups and fed experimental high-fat diets containing fish oil (control diet) or fish oil plus orlistat (200 and 400 mg/kg of diet) over the course of 3 weeks. Fat absorption and the level of eicosapentaenoic acid (EPA) and docosahexaenoic acid, among other fatty acids, in red blood cells, plasma, liver, and spleen, were measured at the end of the experimental period. The results show that at 200 mg and 400 mg/kg of diet orlistat lowers fat absorption by 9% (P = .008) and 54% (P = .008). Orlistat given at the higher level induced a reduction of the incorporation of EPA in red blood cell (-45%; P = .006) and in plasma (-34%; P = .026) compared to the control group. Our results confirmed that administration of orlistat reduces incorporation of n-3 LC-PUFA in blood lipids and tissues in a rat model.

Acylating drugs: redesigning natural covalent inhibitors

Structural modification of naturally occurring beta-lactams and beta-lactones is a highly effective strategy for generating drugs for treating bacterial infections, cancer, obesity, and hyperlipidemia. These drugs acylate catalytic amino acids (serine, threonine, or cysteine) in enzyme targets such as penicillin-binding proteins (PBPs), beta-lactamases, lipases, HMG-CoA reductase, fatty acid synthetase, and the 20S proteasome. Optimally performing drugs combine features of high target affinity, chemoselective reactivity, and high stability of the acylated target protein. This review provides a perspective on these two classes of acylating agents and summarizes recent advances in mechanism and structure-based design of acylating drugs.

A high-throughput screen for endothelial lipase using HDL as substrate

Endothelial lipase (EL) is a 482-amino-acid protein from the triglyceride lipase gene family that uses a Ser-His-Asp triad for catalysis. Its expression in endothelial cells and preference for phospholipids rather than triglycerides are unique. Animal models in which it is overexpressed or knocked out indicate EL levels are inversely correlated with high-density lipoprotein cholesterol (HDL-C). HDL-C is commonly referred to as the good form of cholesterol because it is involved in the reverse cholesterol transport pathway, in which excess cholesterol is effluxed from peripheral tissues for excretion or reabsorption. Thus, EL inhibition in humans is expected to lead to increases in HDL levels and possibly a decrease in cardiovascular disease. To discover inhibitors of EL, a coupled assay for EL has been developed, using its native substrate, HDL. Hydrolysis of HDL by EL yields free fatty acids, which are coupled through acyl-CoA synthetase, acyl-CoA oxidase, and horseradish peroxidase to produce the fluorescent species resorufin. This assay was developed into a 5-microL, 1536-well assay format, and a high-throughput screen was executed against the GSK collection. In addition to describing the screening results, novel post-HTS mechanism-of-action studies were developed for EL and applied to 1 of the screening hits as an example.