Immobilization of chiral enzyme inhibitors on solid supports by amide-forming coupling and olefin metathesis

Direct Aryloxylation/Alkyloxylation of Dialkyl Phosphonates for the Synthesis of Mixed Phosphonates

A strategy for the direct functionalization strategy of inertial dialkyl phosphonates with hydroxy compounds to afford diverse mixed phosphonates with good yields and functional-group tolerance has been developed. Mechanistic investigations involving both NMR studies and DFT studies suggest that an unprecedented highly reactive P^V species (phosphoryl pyridin-1-ium salt), a key intermediate for this new synthetic transformation, is generated in situ from dialkyl phosphonate in the presence of Tf₂ O/pyridine.

Comparison of Zirconium Phosphonate-Modified Surfaces for Immobilizing Phosphopeptides and Phosphate-Tagged Proteins

Different routes for preparing zirconium phosphonate-modified surfaces for immobilizing biomolecular probes are compared. Two chemical-modification approaches were explored to form self-assembled monolayers on commercially available primary amine-functionalized slides, and the resulting surfaces were compared to well-characterized zirconium phosphonate monolayer-modified supports prepared using Langmuir-Blodgett methods. When using POCl3 as the amine phosphorylating agent followed by treatment with zirconyl chloride, the result was not a zirconium-phosphonate monolayer, as commonly assumed in the literature, but rather the process gives adsorbed zirconium oxide/hydroxide species and to a lower extent adsorbed zirconium phosphate and/or phosphonate. Reactions giving rise to these products were modeled in homogeneous-phase studies. Nevertheless, each of the three modified surfaces effectively immobilized phosphopeptides and phosphopeptide tags fused to an affinity protein. Unexpectedly, the zirconium oxide/hydroxide modified surface, formed by treating the amine-coated slides with POCl3/Zr(4+), afforded better immobilization of the peptides and proteins and efficient capture of their targets.

Synthesis and characterization of dual-functionalized core-shell fluorescent microspheres for bioconjugation and cellular delivery

The efficient transport of micron-sized beads into cells, via a non-endocytosis mediated mechanism, has only recently been described. As such there is considerable scope for optimization and exploitation of this procedure to enable imaging and sensing applications to be realized. Herein, we report the design, synthesis and characterization of fluorescent microsphere-based cellular delivery agents that can also carry biological cargoes. These core-shell polymer microspheres possess two distinct chemical environments; the core is hydrophobic and can be labeled with fluorescent dye, to permit visual tracking of the microsphere during and after cellular delivery, whilst the outer shell renders the external surfaces of the microspheres hydrophilic, thus facilitating both bioconjugation and cellular compatibility. Cross-linked core particles were prepared in a dispersion polymerization reaction employing styrene, divinylbenzene and a thiol-functionalized co-monomer. These core particles were then shelled in a seeded emulsion polymerization reaction, employing styrene, divinylbenzene and methacrylic acid, to generate orthogonally functionalized core-shell microspheres which were internally labeled via the core thiol moieties through reaction with a thiol reactive dye (DY630-maleimide). Following internal labeling, bioconjugation of green fluorescent protein (GFP) to their carboxyl-functionalized surfaces was successfully accomplished using standard coupling protocols. The resultant dual-labeled microspheres were visualized by both of the fully resolvable fluorescence emissions of their cores (DY630) and shells (GFP). In vitro cellular uptake of these microspheres by HeLa cells was demonstrated conventionally by fluorescence-based flow cytometry, whilst MTT assays demonstrated that 92% of HeLa cells remained viable after uptake. Due to their size and surface functionalities, these far-red-labeled microspheres are ideal candidates for in vitro, cellular delivery of proteins.

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.

Microbial lipases: at the interface of aqueous and non-aqueous media. A review

In recent times, biotechnological applications of microbial lipases in synthesis of many organic molecules have rapidly increased in non-aqueous media. Microbial lipases are the 'working horses' in biocatalysis and have been extensively studied when their exceptionally high stability in non-aqueous media has been discovered. Stability of lipases in organic solvents makes them commercially feasibile in the enzymatic esterification reactions. Their stability is affected by temperature, reaction medium, water concentration and by the biocatalyst's preparation. An optimization process for ester synthesis from pilot scale to industrial scale in the reaction medium is discussed. The water released during the esterification process can be controlled over a wide range and has a profound effect on the activity of the lipases. Approaches to lipase catalysis like protein engineering, directed evolution and metagenome approach were studied. This review reports the recent development in the field ofnon-aqueous microbial lipase catalysis and factors controlling the esterification/transesterification processes in organic media.

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.

Glutaraldehyde Cross-Linking of Lipases Adsorbed on Aminated Supports in the Presence of Detergents Leads to Improved Performance

Lipases from Candida rugosa (CRL) and lipase isoforms A and B from Candida antarctica (CAL-A and CAL-B) were adsorbed on aminated supports in the presence of detergents to have individual lipase molecules. Then, one fraction was washed to eliminate the detergent, and both preparations were treated with glutaraldehyde. The presence of detergent during the cross-linking of the lipases to the support permitted an increase in the recovered activity (in some instances, even by a 10-fold factor). This activity was higher even than that exhibited by the just adsorbed lipases, suggesting that it was not a result of some protective effect of the detergent in the enzyme activity during glutaraldehyde chemical modification. Moreover, the enantioselectivity of the different enzyme preparations was very different if the glutaraldehyde was offered in the presence or in the absence of detergent, in some cases increasing the E value (even by a 7-fold factor in the case of CAL-A in the hydrolysis of (+/-)-2-hydroxy-4-phenylbutyric acid ethyl ester), in other cases even inverting the enantio preference (e.g., in the case of CRL). The irreversible chemical inhibition of the enzyme that was immobilized and cross-linked with glutaraldehyde in the presence of detergents was more rapid than that in the other preparations (by more than a 10-fold factor). This experiment reveals an exposition degree of the active serine in the preparation cross-linked with the support in the presence of detergent that is higher than that in the other preparations. The results suggested that different enzyme structures were "stabilized" by the glutaraldehyde treatment if performed in the presence or in the absence of detergent, and that, in the presence of detergent, a form of the lipase with the serine residue more exposed to the medium and much more active could be obtained. This strategy seems to be of general use to improve the lipase activity to be used in macroaqueous media.

Separation methods applicable to the evaluation of enzyme-inhibitor and enzyme-substrate interactions

Enzymes catalyze a rich variety of metabolic transformations, and do so with very high catalytic rates under mild conditions, and with high reaction regioselectivity and stereospecificity. These characteristics make biocatalysis highly attractive from the perspectives of biotechnology, analytical chemistry, and organic synthesis. This review, containing 128 references, focuses on the use of separation techniques in the elucidation of enzyme-inhibitor and enzyme-substrate interactions. While coverage of the literature is selective, a broad perspective is maintained. Topics considered include chromatographic methods with soluble or immobilized enzymes, capillary electrophoresis, biomolecular interaction analysis tandem mass spectrometry (BIA-MS), phage and ribosomal display, and immobilized enzyme reactors (IMERs). Examples were selected to demonstrate the relevance and application of these methods for determining enzyme kinetic parameters, ranking of enzyme inhibitors, and stereoselective synthesis and separation of chiral entities.

Use of immobilized lipases for lipase purification via specific lipase–lipase interactions

Lipase from Pseudomonas fluorescens (PFL), an enzyme with a great tendency to yield bimolecular aggregates, was immobilized via multipoint covalent attachment on glyoxyl-agarose in the presence of Triton X-100. This strategy permitted to obtain the enzyme with the active center oriented towards the reaction medium. This immobilized enzyme presents the capacity of specifically adsorbing PFL molecules, that can be easily desorbed by the use of detergents. More interesting, the enzyme was also able to adsorb other lipases. That is, the lipase from Bacillus thermocatenulatus (BTL2) cloned in Escherichia coli was selectively adsorbed on this immobilized enzyme, enabling a very simple purification strategy. Similar results were achieved with some other lipases (those from Rhizomucor miehei (RML), Rhizopus oryzae (ROL), and Humicola Lanuginosa (HLL)). In all cases, the enzyme could be easily desorbed by incubation with Triton X-100. The matrix could be used several cycles without any detrimental effect on the adsorption capacity.

Binding of phage displayed Bacillus subtilis lipase A to a phosphonate suicide inhibitor

Phage display can be used as a protein engineering tool to select proteins with desirable binding properties from a library of randomly constructed mutants. Here, we describe the development of this method for the directed evolution of Bacillus subtilis lipase A, an enzyme that has marked properties for the preparation of pharmaceutically relevant chiral compounds. The lipase gene was cloned upstream of the phage g3p encoding sequence and downstream of a modified g3p signal sequence. Consequently, the enzyme was displayed at the surface of bacteriophage fd as a fusion to its minor coat protein g3p. The phage-bound lipase was correctly folded and fully enzymatically active as determined from the hydrolysis of p-nitrophenylcaprylate with K(m)-values of 0.38 and 0.33 mM for the phage displayed and soluble lipase, respectively. Both soluble lipase and lipase expressed on bacteriophages reacted covalently with a phosphonate suicide inhibitor. The phage does not hamper lipase binding, since both soluble and phage-bound lipase have a similar half-life of inactivation of approximately 5 min. Therefore, we conclude that the Bacillus lipase can be functionally expressed on bacteriophages as a fusion to the phage coat protein g3p. The specific interaction with the suicide inhibitor offers a fast and reproducible method for the future selection of mutant enzymes with an enantioselectivity towards new substrates.