Chaperone function in organic co-solvents: experimental characterization and modeling of a hyperthermophilic chaperone subunit from Methanocaldococcus jannaschii

Novel Chaperones RrGroEL and RrGroES for Activity and Stability Enhancement of Nitrilase in Escherichia coli and Rhodococcus ruber

For large-scale bioproduction, thermal stability is a crucial property for most industrial enzymes. A new method to improve both the thermal stability and activity of enzymes is of great significance. In this work, the novel chaperones RrGroEL and RrGroES from Rhodococcus ruber, a nontypical actinomycete with high organic solvent tolerance, were evaluated and applied for thermal stability and activity enhancement of a model enzyme, nitrilase. Two expression strategies, namely, fusion expression and co-expression, were compared in two different hosts, E. coli and R. ruber. In the E. coli host, fusion expression of nitrilase with either RrGroES or RrGroEL significantly enhanced nitrilase thermal stability (4.8-fold and 10.6-fold, respectively) but at the expense of enzyme activity (32-47% reduction). The co-expression strategy was applied in R. ruber via either a plasmid-only or genome-plus-plasmid method. Through integration of the nitrilase gene into the R. ruber genome at the site of nitrile hydratase (NHase) gene via CRISPR/Cas9 technology and overexpression of RrGroES or RrGroEL with a plasmid, the engineered strains R. ruber TH3 dNHase::RrNit (pNV18.1-Pami-RrNit-Pami-RrGroES) and TH3 dNHase::RrNit (pNV18.1-Pami-RrNit-Pami-RrGroEL) were constructed and showed remarkably enhanced nitrilase activity and thermal stability. In particular, the RrGroEL and nitrilase co-expressing mutant showed the best performance, with nitrilase activity and thermal stability 1.3- and 8.4-fold greater than that of the control TH3 (pNV18.1-Pami-RrNit), respectively. These findings are of great value for production of diverse chemicals using free bacterial cells as biocatalysts.

Functional expression of a penicillin acylase from the extreme thermophile Thermus thermophilus HB27 in Escherichia coli

Background

Penicillin acylases (PACs) are enzymes of industrial relevance in the manufacture of β-lactam antibiotics. Development of a PAC with a longer half-life under the reaction conditions used is essential for the improvement of the operational stability of the process. A gene encoding a homologue to Escherichia coli PAC was found in the genome of the thermophilic bacterium Thermus thermophilus (Tth) HB27. Because of the nature of this PAC and its complex maturation that is crucial to reach its functional heterodimeric final conformation, the overexpression of this enzyme in a heterologous mesophilic host was a challenge. Here we describe the purification and characterization of the PAC protein from Tth HB27 overexpressed in Escherichia coli.

Results

Fusions to a superfolder green fluorescent protein and differential membrane solubilization assays indicated that the native enzyme remains attached through its amino-terminal end to the outer side of the cytoplasmic membrane of Tth cells. In order to overexpress this PAC in E. coli cells, a variant of the protein devoid of its membrane anchoring segment was constructed. The effect of the co-expression of chaperones and calcium supplementation of the culture medium was investigated. The total production of PAC was enhanced by the presence of DnaK/J and GrpE and even more by trigger factor and GroEL/ES. In addition, 10 mM calcium markedly improved both PAC specific and volumetric activities. Recombinant PAC was affinity-purified and proper maturation of the protein was confirmed by SDS-PAGE and MALDI-TOF analysis of the subunits. The recombinant protein was tested for activity towards several penicillins, cephalosporins and homoserine lactones. Hydrophobic acyl-chain penicillins were preferred over the rest of the substrates. Penicillin K (octanoyl penicillin) was the best substrate, with the highest specificity constant value (16.12 mM^-1.seg^-1). The optimum pH was aprox. 4 and the optimum temperature was 75 °C. The half-life of the enzyme at this temperature was 9.2 h.

Conclusions

This is the first report concerning the heterologous expression of a pac gene from a thermophilic microorganism in the mesophilic host E. coli. The recombinant protein was identified as a penicillin K-deacylating thermozyme.

Inhibition of heat- and chemical-induced aggregation of various proteins reveals chaperone-like activity of the acute-phase component and serine protease inhibitor human alpha(1)-antitrypsin

In vitro chaperone-like activity of the serpin family member and plasma acute-phase component human alpha(1)-antitrypsin (AAT) has been shown for the first time. Results of light-scattering experiments demonstrated that AAT efficiently inhibits both heat- and chemical-induced aggregation of various test proteins including alcohol dehydrogenase, aldolase, carbonic anhydrase, catalase, citrate synthase, enolase, glutathione S-transferase, l-lactate dehydrogenase, and beta(L)-crystallin. The results suggest that the unique metastable serpin architecture enables dual function, protease inhibiton as well as chaperone activity and highlight the serpin superfamily as a possible source of additional intra- and extracellular chaperones (e.g. alpha(1)-antichymotrypsin). The present finding is surprising in the light of the well-known role of mutated forms of AAT and other serpins in the pathogenesis of diseases called serpinopathies that featured with aberrant conformational transitions and consequent self-aggregation of serpin proteins.

A potentially versatile nucleotide hydrolysis activity of group II chaperonin monomers from Thermoplasma acidophilum

Compared to the group I chaperonins such as Escherichia coli GroEL, which facilitate protein folding, many aspects of the functional mechanism of archaeal group II chaperonins are still unclear. Here, we show that monomeric forms of archaeal group II chaperonin alpha and beta from Thermoplasma acidophilum may be purified stably and that these monomers display a strong AMPase activity in the presence of divalent ions, especially Co(2+) ion, in addition to ATPase and ADPase activities. Furthermore, other nucleoside phosphates (guanosine, cytidine, uridine, and inosine phosphates) in addition to adenine nucleotides were hydrolyzed. From analyses of the products of hydrolysis using HPLC, it was revealed that the monomeric chaperonin successively hydrolyzed the phosphoanhydride and phosphoester bonds of ATP in the order of gamma to alpha. This activity was strongly suppressed by point mutation of specific essential aspartic acid residues. Although these archaeal monomeric chaperonins did not alter the refolding of MDH, their novel versatile nucleotide hydrolysis activity might fulfill a new function. Western blot experiments demonstrated that the monomeric chaperonin subunits were also present in lysed cell extracts of T. acidophilum, and partially purified native monomer displayed Co(2+)-dependent AMPase activity.

Redirecting the inactivation pathway of penicillin amidase and increasing amoxicillin production via a thermophilic molecular chaperone

We have previously shown that a single-subunit thermosome from Methanocaldococcus jannaschii (rTHS) can stabilize enzymes in semi-aqueous media (Bergeron et al., 2008b). In the present study, rTHS was used to stabilize penicillin amidase (PGA) in methanol-water mixtures. Including methanol in the reaction medium for amoxicillin synthesis can suppress unwanted hydrolysis reactions but inactivate PGA. Inactivation and reactivation pathways proposed for PGA illustrate the predictability of enzyme stabilization by rTHS in co-solvents. Calcium was necessary for reversible dissociation of the two PGA subunits in methanol-water and the presence of calcium resulted in an enhancement of chaperone-assisted stabilization. rTHS also acted as a stabilizer in the enzymatic synthesis of the beta-lactam antibiotic amoxicillin. rTHS stabilized PGA, increasing its half-life in 35% methanol by fivefold at 37 degrees C. Stabilization by rTHS was enhanced but did not require the presence of ATP. Including rTHS in fed-batch reactions performed in methanol-water resulted in nearly 4 times more amoxicillin than when the reaction was run without rTHS, and over threefold higher selectivity towards amoxicillin synthesis compared to aqueous conditions without rTHS. The thermosome and other thermophilic chaperones may thus be generally useful for stabilizing enzymes in their soluble form and expanding the range of conditions suitable for biocatalysis.

Identification of a critical chaperoning region on an archaeal recombinant thermosome

Chaperone function in water-miscible organic co-solvents is useful for biocatalytic applications requiring enzyme stability in semi-aqueous media and for understanding chaperone behavior in hydrophobic environments. Previously, we have shown that a recombinant single subunit thermosome (rTHS) from Methanocaldococcus jannaschii functions in multiple co-solvents to hydrolyze ATP, prevent protein aggregation, and refold enzymes following solvent denaturation. For the present study, a truncated analog to the thermosome in which 70 N-terminal amino acids are removed is used to identify important regions within the thermosome for its chaperoning functions in organic co-solvents. Data presented herein indicate that the N-terminal region of rTHS is essential for the chaperone to restore the native state of the enzyme citrate synthase, but it is not a critical region for either binding of unfolded proteins or ATP hydrolysis. This is the first demonstration that direct refolding by a Group II chaperonin requires the N-terminal region of the protein.