Effect of water and enzyme concentration on thermolysin-catalyzed solid-to-solid peptide synthesis

Reactive crystallization: a review

Reactive crystallization is not new, but there has been recent growth in its use as a means of improving performance and sustainability of industrial processes.

Recent trends in biocatalysis engineering

During the last 30 years the scope of biocatalysis has been expanding due to the advances in several technological fields. Diverse techniques as structural enzyme improvement (e.g. protein engineering, direct evolution), engineering approaches (e.g. ionic liquids, supercritical fluids) and physical stabilization (e.g. immobilization, CLEAS) have been developed, which in combination are powerful tools to improve biotransformation and to synthesize new products. In the present work, recent advances in biocatalysis are reviewed.

Peptide synthesis catalysed by a haloalkaliphilic serine protease from the archaeon Natrialba magadii (Nep)

AIMS

Haloarchaeal proteases function optimally in high salt (low water activity); thus, they offer an advantage over the nonhalophilic counterparts as biocatalysts for protease-catalysed peptide synthesis. The haloalkaliphilic archaeon Natrialba magadii secretes a solvent-tolerant protease, Nep (Natrialba magadii extracellular protease). In this work, the ability of Nep to catalyse peptide synthesis was examined.

METHODS AND RESULTS

The tripeptide Ac-Phe-Gly-Phe-NH(2) was synthesized using Ac-Phe-OEt and Gly-Phe-NH(2) substrates as building blocks in the presence of Nep, 30% (v/v) dimethyl sulfoxide (DMSO) and 1.5 or 0.5 mol l(-1) NaCl. Purification and identification of the peptide product was achieved by RP-HPLC and ESI-MS, respectively. The native as well as the recombinant enzyme produced in Haloferax volcanii (HvNep) was similarly effective as catalysts for the synthesis of this model tripeptide with yields of up to 60% and without secondary hydrolysis of the product. HvNep catalysed the synthesis of various tripeptides with preference for those having aromatic amino acids in the P1 site.

CONCLUSION

Nep is able to catalyse peptide synthesis under different salt concentrations in the presence of DMSO.

SIGNIFICANCE AND IMPACT OF STUDY

The catalytic property of Nep in peptide synthesis combined with overproduction of this protease in Hfx. volcanii anticipates the potential applicability of this haloarchaeal protease in biotechnology.

Enzymes in organic media

Enzyme catalysis in low water containing organic solvents is finding an increasing number of applications in diverse areas. This review focuses on some aspects which have not been reviewed elsewhere. Different strategies for obtaining higher activity and stability in such media are described. In this context, the damaging role of lyophilization and the means of overcoming such effects are discussed. Ultrasonication and microwave assistance are two emerging approaches for enhancing reaction rates in low water media. Control of water activity and medium engineering are two crucial approaches in optimization of catalytic behaviour in nonaqueous enzymology. Organometallics and synthesis/modification of polymers are two areas where nonaqueous enzymology can play a greater role in the coming years. The greater understanding of enzyme behaviour in nonaqueous media is expected to lead to larger and even more diverse kinds of applications.

Solvent selection for solid-to-solid synthesis

Thermolysin catalyzed solid-to-solid synthesis of the model peptide Z-L-Phe-L-Leu-NH(2) is practically feasible in water and a range of organic solvents with different physicochemical properties. Excellent overall conversions were obtained in acetonitrile, ethyl acetate, n-hexane, methanol, 2-propanol, tert-amyl alcohol, tetrahydrofuran, toluene and water, while no product precipitation was observed in dichloromethane resulting in a much lower yield. In precipitation driven synthesis the product accumulates both in solution and in the solid phase. It was shown that the highest overall yields (yield in the liquid plus yield in the solid) can be expected in solvents where the substrate solubilities are minimized. The best yields of solid product can be expected in solvents where both product and substrate solubilities are lowest. This was in agreement with experimental observations and should be generally valid.

Predicting when precipitation-driven synthesis is feasible: application to biocatalysis

Precipitation-driven synthesis offers the possibility of obtaining high reaction yields using very low volume reactors and is finding increasing applications in biocatalysis. Here, a model that allows straightforward prediction of when such a precipitation-driven reaction will be thermodynamically feasible is presented. This requires comparison of the equilibrium constant, Keq, with the saturated mass action ratio, Zsat, defined as the ratio of product solubilities to reactant solubilities. A hypothetical thermodynamic cycle that can be used to accurately predict Zsat, in water is described. The cycle involves three main processes: fusion of a solid to a supercooled liquid, ideal mixing of the liquid with octanol, and partitioning from octanol to water. To obtain the saturated mass action ratio using this cycle, only the melting points of the reactants and products, and in certain cases the pKa of ionisable groups, are required as input parameters. The model was tested on a range of enzyme-catalysed peptide syntheses from the literature and found to predict accurately when precipitation-driven reaction was possible. The methodology employed is quite general and the model is therefore expected to be applicable to a wide range of other (bio)-catalysed reactions.

Chemo-enzymatic synthesis of arginine-based gemini surfactants

A novel chemo-enzymatic synthesis of arginine-based gemini cationic surfactants bis(Args) is reported. These compounds consist of two single N(alpha)-acyl-arginine structures connected through the alfa-carboxylic groups of the arginine residues by a alpha, omega-diaminoalkane spacer chain. N(alpha)-Acyl-L-arginine alkyl ester derivatives were the starting building blocks for the synthesis. The best strategy found consisted of two steps. First, the quantitative acylation of one amino group of the spacer by the carboxylic ester of the N(alpha)-acyl-arginine took place spontaneously, at the melting point of the alpha,omega-diaminoalkane, in a solvent-free system. The second step was the papain-catalyzed reaction between another N(alpha)-acyl-arginine alkyl ester and the free aliphatic amino group of the derivative formed in the first step. Reactions were carried out in solid-to-solid and solution systems using low-toxic potential solvents. Changes in reaction performance and product yield were studied for the following variables: organic solvent, support for enzyme deposition and substrate concentration. The best yields (70%) were achieved in solid-to-solid systems and in ethanol at a(w) = 0.07. Bis(Args) analogs of 8, 10 and 12 carbon atoms using 1,3-diaminopropane and 1, 3-diamino-2-hydroxy-propane as hydrocarbon spacers were prepared at the 6-7 gram level employing the methodology developed. The overall yields which include reaction and purification varied from 51% to 65% of pure (97-98% by HPLC) product.