Crystallization of a novel α-amylase, AmyB, from the thermophilic halophileHalothermothrix orenii

A highly thermoactive and salt-tolerant α-amylase isolated from a pilot-plant biogas reactor

Aiming at the isolation of novel enzymes from previously uncultured thermophilic microorganisms, a metagenome library was constructed from DNA isolated from a pilot-plant biogas reactor operating at 55 °C. The library was screened for starch-degrading enzymes, and one active clone was found. An open reading frame of 1,461 bp encoding an α-amylase from an uncultured organism was identified. The amy13A gene was cloned in Escherichia coli, resulting in high-level expression of the recombinant amylase. The novel enzyme Amy13A showed the highest sequence identity (75%) to α-amylases from Petrotoga mobilis and Halothermothrix orenii. Amy13A is highly thermoactive, exhibiting optimal activity at 80 °C, and it is also highly salt-tolerant, being active in 25% (w/v) NaCl. Amy13A is one of the few enzymes that tolerate high concentrations of salt and elevated temperatures, making it a potential candidate for starch processing under extreme conditions.

Expression, purification, crystallization and preliminary X-ray diffraction analysis of a ribokinase from the thermohalophile Halothermothrix orenii

A ribokinase gene (rbk) from the anaerobic halothermophilic bacterium Halothermothrix orenii was cloned and overexpressed in Escherichia coli. The recombinant protein (Ho-Rbk) was purified using immobilized metal-ion affinity chromatography and crystals were obtained using the sitting-drop method. Diffraction data were collected to a resolution of 3.1 Å using synchrotron radiation. The crystals belonged to the orthorhombic space group P2(1)2(1)2(1), with unit-cell parameters a = 45.6, b = 61.1, c = 220.2, and contained two molecules per asymmetric unit. A molecular-replacement solution has been found and attempts are currently under way to build a model of the ribokinase. Efforts to improve crystal quality so that higher resolution data can be obtained are also being considered.

Expression, purification and preliminary crystallographic analysis of the recombinant β-glucosidase (BglA) from the halothermophile Halothermothrix orenii

The β-glucosidase A gene (bglA) has been cloned from the halothermophilic bacterium Halothermothrix orenii and the recombinant enzyme (BglA; EC 3.2.1.21) was bacterially expressed, purified using metal ion-affinity chromatography and subsequently crystallized. Orthorhombic crystals were obtained that diffracted to a resolution limit of 3.5 Å. The crystal structure with two molecules in the asymmetric unit was solved by molecular replacement using a library of known glucosidase structures. Attempts to collect higher resolution diffraction data from crystals grown under different conditions and structure refinement are currently in progress.

Expression, purification and preliminary crystallographic analysis of sucrose phosphate synthase (SPS) from Halothermothrix orenii

This is the first report of the crystallization of a sucrose phosphate synthase (SPS; EC 2.4.1.14). It also constitutes the first study of a sucrose phosphate synthase from a non-photosynthetic thermohalophilic anaerobic bacterium, Halothermothrix orenii. The purified recombinant spsA protein has been crystallized in the monoclinic space group C2, with unit-cell parameters a = 154.2, b = 47.9, c = 72.3 A, beta = 103.16 degrees, using the hanging-drop vapour-diffusion method. The crystal diffracts X-rays to a resolution limit of 3.01 A. Heavy-metal and halide-soaking trials are currently in progress to solve the structure.