Adipose triglyceride lipase (ATGL) and hormone-sensitive lipase (HSL) deficiencies affect expression of lipolytic activities in mouse adipose tissues.

Adipose triglyceride lipase (ATGL) and hormone-sensitive lipase (HSL) are key enzymes involved in intracellular degradation of triacylglycerols. It was the aim of this study to elucidate how the deficiency in one of these proteins affects the residual lipolytic proteome in adipose tissue. For this purpose, we compared the lipase patterns of brown and white adipose tissue from ATGL (-/-) and HSL (-/-) mice using differential activity-based gel electrophoresis. This method is based on activity-recognition probes possessing the same substrate analogous structure but carrying different fluorophores for specific detection of the enzyme patterns of two different tissues in one electrophoresis gel. We found that ATGL-deficiency in brown adipose tissue had a profound effect on the expression levels of other lipolytic and esterolytic enzymes in this tissue, whereas HSL-deficiency hardly showed any effect in brown adipose tissue. Neither ATGL- nor HSL-deficiency greatly influenced the lipase patterns in white adipose tissue. Enzyme activities of mouse tissues on acylglycerol substrates were analyzed as well, showing that ATGL-and HSL-deficiencies can be compensated for at least in part by other enzymes. The proteins that responded to ATGL-deficiency in brown adipose tissue were overexpressed and their activities on acylglycerols were analyzed. Among these enzymes, Es1, Es10, and Es31-like represent lipase candidates as they catalyze the hydrolysis of long-chain acylglycerols.

Differential activity-based gel electrophoresis for comparative analysis of lipolytic and esterolytic activities.

We established a novel technique for differential activity-based gel electrophoresis (DABGE) of lipolytic enzymes from two different biological samples. For this purpose, a set of three fluorescent suicide inhibitors was developed. These probes possess the same substrate analogous structures but carry different cyanine dyes (Cy2b, Cy3, and Cy5) as reporter fluorophores. For comparison of enzyme profiles, two samples are individually labeled with a different probe followed by mixing, gel electrophoresis, fluorescence imaging, and identification of the tagged proteins by MS/MS. Protocols for quantitative determination of active enzymes were developed on the basis of lipolytic proteomes that had been admixed with defined amounts of known lipases and esterases. A detailed analysis of the fluorescence intensities showed that the found enzyme ratios very closely reflected the relative amounts of the labeled enzymes that were used for spiking. The DABGE method was used to compare the lipolytic proteomes of brown and white adipose tissue showing specific enzyme patterns of both samples. This study represents the first application of this technology for comparative analysis of lipases and esterases. Further applications of this technique can be expected to provide entirely new information on lipid enzymology in health and disease with high precision.

Glycosidase profiling with immobilised glycosidase-inhibiting iminoalditols--a proof-of-concept study.

Three typical glycosidase-inhibiting iminoalditols were attached to a polyamine surface displayed on a silicon chip. Exposure to a representative beta-glucosidase revealed selective binding events reflecting the different structural features of the inhibitors probed in this study. This provides a proof-of-concept for the successful exploitation of microarrays of typical reversible glycosidase inhibitors of the iminosugar family.

N(pro) fusion technology to produce proteins with authentic N termini in E. coli.

We describe a prokaryotic expression system using the autoproteolytic function of N(pro) from classical swine fever virus. Proteins or peptides expressed as N(pro) fusions are deposited as inclusion bodies. On in vitro refolding by switching from chaotropic to kosmotropic conditions, the fusion partner is released from the C-terminal end of the autoprotease by self-cleavage, leaving the target protein with an authentic N terminus. A tailor-made N(pro) mutant called EDDIE, with increased in vitro and decreased in vivo cleavage rates, has enabled us to express proinsulin, domain-D of staphylococcal protein A, hepcidin, interferon-alpha1, keratin-associated protein 10-4, green fluorescent protein, inhibitorial peptide of senescence-evasion-factor, monocyte chemoattractant protein-1 and toxic gyrase inhibitor, among others. This N(pro) expression system can be used as a generic tool for the high-level production of recombinant toxic peptides and proteins (up to 12 g/l) in Escherichia coli without the need for chemical or enzymatic removal of the fusion tag.

Insights into molecular medicine: development of new diagnostic and prognostic parameters.

Molecular medicine leads us towards an understanding of some diseases at the molecular level. Examples are the analysis of immune complexes and receptor-antireceptor compounds used in clinical medicine. Structural changes of some serum proteins occur in inflammation, neoplasia and autoimmunity. The detection and analysis of such structural modifications may offer a new field for the diagnosis, prognosis and therapy of some diseases. Modern medicine requires new technologies with high sensitivity, specificity and applicability. For the first time in Austria we have combined fluorescence correlation spectroscope (FCS), surface enhanced laser desorption ionisation--time of flight (SELDI-TOF) and the molecular modelling and visualization system according to the computer enhanced programs. Experimental and computational methods are combined in such a way that clinical data can be interpreted by theoretical methods at a molecular level or vice versa, the computational output delivers input for new investigations. One method brings us single results. In view of the spectrum of parameters relevant to clinical entities, multiplexing is a new way of development. Since the technologies are new, the scientifically interested reader should be informed about the matters arising.

A versatile library of activity-based probes for fluorescence detection and/or affinity isolation of lipolytic enzymes.

This work describes the synthesis of a library of fluorescent and/or biotinylated alkylphosphonate inhibitors being reactive towards serine hydrolases, especially lipases and esterases. Fluorescent inhibitors can be used for sensitive and rapid detection of active proteins by gel electrophoresis. Biotinylated inhibitors are applicable for the enrichment and isolation of active enzymes. Functionality as well as the different detection methods of the synthesized inhibitors were successfully tested with an enzyme preparation, namely cholesterol esterase from porcine pancreas (ppCE). Moreover, a biotinylated inhibitor was employed to enrich ppCE on avidin beads. Hence, our set of phosphonate inhibitors can be used for the detection and/or isolation of active serine hydrolases.

Inhibitor and protein microarrays for activity-based recognition of lipolytic enzymes.

Protein and small-molecule microarrays are useful tools for high-throughput analysis of DNA-protein, protein-protein, and protein-small molecule interactions. Here we report on novel microarrays for activity screening of lipases and esterases based on phosphonic acid ester inhibitors. These compounds are activity recognition probes (ARPs) and bind to active serine hydrolases in a stoichiometric and irreversible manner. Protein microarrays were generated by spotting six different lipolytic enzymes onto hydrogel-coated glass slides. The activity of immobilized enzymes was determined after treatment with fluorescently labeled ARPs. Alternatively, biotinylated ARPs were bound to streptavidin slides in order to identify their affinity for enzymes in solution. Both systems, the protein- and ARP microarrays proved to be useful and versatile tools for the rapid identification and characterization of novel and known lipolytic enzymes.

Novel fluorescent phosphonic acid esters for discrimination of lipases and esterases.

Lipases and esterases are responsible for carboxylester hydrolysis inside and outside cells and are useful biocatalysts for (stereo)selective modification of synthetic substrates. Here we describe novel fluorescent suicide inhibitors that differ in structure and polarity for screening and discrimination of lipolytic enzymes in enzyme preparations. The inhibitors covalently react with the enzymes to form fluorescent lipid-protein complexes that can be resolved by gel electrophoresis. The selectivities of the inhibitors were determined by using different (phospho)lipase, esterase and cholesterol esterase preparations. The results indicate that formation of an inhibitor-enzyme complex is highly dependent on the chemical structure of the inhibitor. We identified inhibitors with very low specificity, and other derivatives that were highly specific for certain subgroups of lipolytic enzymes such as lipases and cholesterol esterases. A combination of these substrate-analogous activity probes represents a useful toolbox for rapid identification and classification of serine hydrolase enzymes.

The lipolytic proteome of mouse adipose tissue.

Hydrolysis of triacylglycerols and cholesteryl esters is a key event in energy homeostasis of animals. However, many lipolytic activities still await their molecular identification. Here we report on a novel tool for concomitant analysis of lipases in complex proteomes. Fluorescent activity tags mimicking lipid substrates were used to label the proteome of mouse adipose tissue. Analysis by two-dimensional gel electrophoresis and LC-MS/MS led to the identification of all known intracellular lipases as well as a number of novel candidates. One of them was recently shown to be involved in triacylglycerol mobilization in adipocytes and therefore named adipose triglyceride lipase. Functional characterization of expressed enzymes demonstrated that lipolytic and esterolytic activities could be well discriminated. Thus our results show the first map of the lipolytic proteome of mouse adipose tissue and demonstrate the general applicability of our method for rapid profiling and identification of lipolytic activities in complex biological samples.