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Purification and properties of an aryl beta-xylosidase from a cellulolytic extreme thermophile expressed in Escherichia coli.

ABSTRACT: An aryl beta-xylosidase was purified to homogeneity from an Escherichia coli strain containing a recombinant plasmid carrying a beta-xylosidase (EC 3.2.1.37) gene from the extremely thermophilic anaerobic bacterium isolate Tp8T6.3.3.1 ('Caldocellum saccharolyticum'). It has a pI of 4.3 and shows optimal activity at pH 5.7. The enzyme is highly specific, acting on o- and p-nitrophenyl beta-D-xylopyranosides and minimally on p-nitrophenyl alpha-L-arabinopyranoside. It does not act on xylobiose. The Km for p-nitrophenyl beta-D-xylopyranoside at the optimum pH for activity is 10 mM, and at pH 7.0 is 6.7 mM. Xylose is a competitive inhibitor with Ki 40 mM. Thermal inactivation follows first-order kinetics at 65 and 70 degrees C with t1/2 values of 4.85 h and 40 min respectively. The t1/2 at 70 degrees C is increased 3-fold and 4-fold by the addition of 0.5 mg of BSA/ml and 2 mM-dithiothreitol respectively.

SUBMITTER: Hudson RC

PROVIDER: S-EPMC1150217 | biostudies-other | 1991 Feb

REPOSITORIES: biostudies-other

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Project description:BackgroundPenicillin 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.ResultsFusions 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.ConclusionsThis 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.

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Purification and properties of an aryl beta-xylosidase from a cellulolytic extreme thermophile expressed in Escherichia coli.

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