DSC studies of Fusarium solani pisi cutinase: consequences for stability in the presence of surfactants

Experimental and mathematical modeling approaches for biocatalytic post-consumer poly(ethylene terephthalate) hydrolysis

The environmental impact arising from poly(ethylene terephthalate) (PET) waste is notable worldwide. Enzymatic PET hydrolysis can provide chemicals that serve as intermediates for value-added product synthesis and savings in the resources. In the present work, some reaction parameters were evaluated on the hydrolysis of post-consumer PET (PC-PET) using a cutinase from Humicola insolens (HiC). The increase in PC-PET specific area leads to an 8.5-fold increase of the initial enzymatic hydrolysis rate (from 0.2 to 1.7 mmol L^-1 h^-1), showing that this parameter plays a crucial role in PET hydrolysis reaction. The effect of HiC concentration was investigated, and the enzymatic PC-PET hydrolysis kinetic parameters were estimated based on three different mathematical models describing heterogeneous biocatalysis. The model that best fits the experimental data (R² = 0.981) indicated 1.68 mg_protein mL^-1 as a maximum value of the enzyme concentration to optimize the reaction rate. The HiC thermal stability was evaluated, considering that it is a key parameter for its efficient use in PET degradation. The enzyme half-life was shown to be 110 h at 70 ºC and pH 7.0, which outperforms most of the known enzymes displaying PET hydrolysis activity. The results evidence that HiC is a very promising biocatalyst for efficient PET depolymerization.

Expression and characterization of a cutinase (AnCUT2) from Aspergillus niger

Cutin hydrolase (EC 3.1.1.74), an extracellular polyesterase found in pollens, bacteria and fungi, is an efficient catalyst that exhibits hydrolytic activity on a variety of water-soluble esters, synthetic fibers, plastics and triglycerides. Thus, cutinase can be used in various applications such as ester synthesis, bio-scouring, food and detergent industries. Ancut2 is one of five genes encoding cutinases present in the Aspergillus niger ATCC 10574 genome. The cDNA of Ancut2 comprising of an open reading frame of 816 bp encoding a protein of 271 amino acid residues, was isolated and expressed in Pichia pastoris. The partially purified recombinant cutinase exhibited a molecular mass of approximately 40 kDa. The enzyme showed highest activity at 40°C with a preference for acidic pH (5.0-6.0). AnCUT2 showed hydrolytic activity towards various p-nitrophenyl esters with preference towards shorter chain esters such as p-nitrophenyl butyrate (C4). Scanning Electron Microscopy demonstrated that AnCUT2 was capable of modifying surfaces of synthetic polycaprolactone and polyethylene terephthalate plastics. The properties of this enzyme suggest that it may be applied in synthetic fiber modification and fruit processing industries.

Thermodynamic and structural investigation of the specific SDS binding of Humicola insolens cutinase

The interaction of lipolytic enzymes with anionic surfactants is of great interest with respect to industrially produced detergents. Here, we report the interaction of cutinase from the thermophilic fungus Humicola insolens with the anionic surfactant SDS, and show the enzyme specifically binds a single SDS molecule under nondenaturing concentrations. Protein interaction with SDS was investigated by NMR, ITC and molecular dynamics simulations. The NMR resonances of the protein were assigned, with large stretches of the protein molecule not showing any detectable resonances. SDS is shown to specifically interact with the loops surrounding the catalytic triad with medium affinity (Ka ≈ 10(5) M(-1) ). The mode of binding is closely similar to that seen previously for binding of amphiphilic molecules and substrate analogues to cutinases, and hence SDS acts as a substrate mimic. In addition, the structure of the enzyme has been solved by X-ray crystallography in its apo form and after cocrystallization with diethyl p-nitrophenyl phosphate (DNPP) leading to a complex with monoethylphosphate (MEP) esterified to the catalytically active serine. The enzyme has the same fold as reported for other cutinases but, unexpectedly, esterification of the active site serine is accompanied by the ethylation of the active site histidine which flips out from its usual position in the triad.

The role of short-range Cys171-Cys178 disulfide bond in maintaining cutinase active site integrity: a molecular dynamics simulation

Understanding structural determinants in enzyme active site integrity can provide a good knowledge to design efficient novel catalytic machineries. Fusarium solani pisi cutinase with classic triad Ser-His-Asp is a promising enzyme to scrutinize these structural determinants. We performed two MD simulations: one, with the native structure, and the other with the broken Cys171-Cys178 disulfide bond. This disulfide bond stabilizes a turn in active site on which catalytic Asp175 is located. Functionally important H-bonds and atomic fluctuations in catalytic pocket have been changed. We proposed that this disulfide bond within active site can be considered as an important determinant of cutinase active site structural integrity.

Thermal Stability of Humicola insolens Cutinase in aqueous SDS

Cutinase from Humicola insolens (HiC) has previously been shown to bind anomalously low amounts of the anionic surfactant sodium dodecylsulfate (SDS). In the current work, we have applied scanning and titration calorimetry to investigate possible relationships between this weak interaction and the effect of SDS on the equilibrium and kinetic stability of HiC. The results are presented in a "state-diagram," which specifies the stable form of the protein as a function of temperature and SDS concentration. In comparison with other proteins, the equilibrium stability HiC is strongly decreased by SDS. For low SDS concentrations (SDS:HiC molar ratio, MR < 8) this trait is also found for the kinetically controlled thermal aggregation of the protein. At higher MR, however, SDS stabilizes noticeably against irreversible aggregation. We suggest that this relies on electrostatic repulsion of the increasingly negatively charged HiC-SDS complexes. The combined interpretation of calorimetric and binding data allowed the calculation of the changes in enthalpy and heat capacity for the association of HiC and SDS near the saturation point. The latter function was about -410 J mol(-1) K(-1) or similar to the heat capacity change for micelle formation (-470 J mol(-1) K(-1)). This suggests that SDS is hydrated to a similar extent in the micellar and protein associated forms. The results are discussed in terms of the Wyman theory for linked equilibria. Quantitative analysis along these lines suggests that the reversible thermal unfolding of the protein couples to the binding of 2-3 additional SDS molecules. This corresponds to a 15-20% increase in the binding number. Wyman theory also rationalizes relationships between low affinity and high susceptibility observed in this study.

The effect of additives and mechanical agitation in surface modification of acrylic fibres by cutinase and esterase

The surface of an acrylic fibre containing about 7% of vinyl acetate was modified using Fusarium solani pisi cutinase and a commercial esterase, Texazym PES. The effect of acrylic solvents and stabilising polyols on cutinase operational stability was studied. The half-life time of cutinase increased by 3.5-fold with the addition of 15% N,N-dimethylacetamide (DMA) and by 3-fold with 1M glycerol. The impact of additives and mechanical agitation in the protein adsorption and in the hydrolysis of vinyl acetate from acrylic fabric was investigated. The hydroxyl groups produced on the surface of the fibre were able to react specifically with Remazol Brilliant Blue R (cotton reactive dye) and to increase the colour of the acrylic-treated fabric. The best staining level was obtained with a high level of mechanical agitation and with the addition of 1% DMA. Under these conditions, the raise in the acrylic fabric colour depth was 30% for cutinase and 25% for Texazym. The crystallinity degree, determined by X-ray diffraction, was not significantly changed between control samples and samples treated with cutinase. The results showed that the outcome of the application of these enzymes depends closely on the reaction media conditions.

Interrelationships of glycosylation and aggregation kinetics for Peniophora lycii phytase

The kinetics of thermally induced aggregation of the glycoprotein Peniophora lycii phytase (Phy) and a deglycosylated form (dgPhy) was studied by dynamic (DLS) and static (SLS) light scattering. This provided a detailed insight into the time course of the formation of small aggregates ( approximately 10-100 molecules) of the enzyme. The thermodynamic stability of the two forms was also investigated using scanning calorimetry (DSC). It was found that the glycans strongly promoted kinetic stability (i.e., reduced the rate of irreversible denaturation) while leaving the equilibrium denaturation temperature, T(d), defined by DSC, largely unaltered. At pH 4.5-5.0, for example, dgPhy aggregated approximately 200 times faster than Phy, even though the difference in T(d) was only 1-3 degrees C. To elucidate the mechanism by which the glycans promote kinetic stability, we measured the effect of ionic strength and temperature on the aggregation rate. Also, the second virial coefficients (B(22)) for the two forms were measured by SLS. These results showed that the aggregation rate of Phy scaled with the concentration of thermally denatured protein. This suggested first-order kinetics with respect to the concentration of the thermally denatured state. A similar but less pronounced correlation was found for dgPhy, and it was suggested that while the aggregation process for the deglycosylated form is dominated by denatured protein, it also involves a smaller contribution from associating molecules in the native state. The measurements of B(22) revealed that dgPhy had slightly higher values than Phy. This suggests that dgPhy interacts more favorably with the buffer than Phy and hence rules out strong hydration of the glycans as the origin of their effect on the kinetic stability. On the basis of this and the effects of pH and ionic strength, we suggest that the inhibition of aggregation is more likely to depend on steric hindrance of the glycans in the aggregated form of the protein.

pH-dependent aggregation of cutinase is efficiently suppressed by 1,8-ANS

We have studied the thermal stability of the triglyceride-hydrolyzing enzyme cutinase from F. solani pisi at pH values straddling the pI (pH 8.0). At the pI, increasing the protein concentration from 5 to 80 microM decreases the apparent melting temperature by 19 degrees C. This effect vanishes at pH values more than one unit away from pI. In contrast to additives such as detergents and osmolytes, the hydrophobic fluorophore 1,8-ANS completely and saturably suppresses this effect, restoring 70% of enzymatic activity upon cooling. ANS binds strongly to native cutinase as a noncompetitive inhibitor with up to 5 ANS per cutinase molecule. Only the first ANS molecule stabilizes cutinase; however, the last 4 ANS molecules decrease Tm by up to 7 degrees C. Similar pI-dependent aggregation and suppression by ANS is observed for T. lanuginosus lipase, but not for lysozyme or porcine alpha-amylase, suggesting that this behavior is most prevalent for proteins with affinity for hydrophobic substrates and consequent exposure of hydrophobic patches. Aggregation may be promoted by a fluctuating ensemble of native-like states associating via intermolecular beta-sheet rich structures unless blocked by ANS. Our data highlight the chaperone activity of small molecules with affinity for hydrophobic surfaces and their potential application as stabilizers at appropriate stoichiometries.