Kinetically controlled refolding of a heat-denatured hyperthermostable protein

Bifunctional immobilization of a hyperthermostable endo-β-1,3-glucanase

Laminarinase A (LamA) from Pyrococcus furiosus is a hyperthermostable endo-β-1,3-glucanase (EC 3.2.1.39) belonging to the glycosyl hydrolase family GH16. Here, we report the two-step immobilization of LamA on macroporous acrylic epoxy beads, extra-functionalized with disulfide groups. To facilitate initial immobilization via thiol-disulfide exchange, we introduced, by site-directed mutagenesis, a superficial cysteine residue near the protein C-terminal end. The thus-obtained S296C variant showed similar catalytic properties as native LamA. The activity of immobilized S296C displayed an inverse relationship with particle size. Use of conventional beads (150-300 μm in diameter) obstructed the catalytic efficiency due to pore diffusion limitation of the polysaccharide substrate. Bifunctional attachment to milled beads (20-40 μm) resulted in high enzyme load and outstanding catalytic features. Bifunctional immobilized S296C showed extreme pH stability and could be repeatedly used at 60 °C without significant activity loss.

Thermal stabilization of an endoglucanase by cyclization

An intein-driven protein splicing approach allowed for the covalent linkage between the N- and C-termini of a polypeptide chain to create circular variants of the endo-β-1,3-1,4-glucanase, LicA, from Bacillus licheniformis. Two circular variants, LicA-C1 and LicA-C2, which have connecting loops of 20 and 14 amino acids, respectively, showed catalytic activities that are approximately two and three times higher, respectively, compared to that of the linear LicA (LicA-L1). The thermal stability of the circular variants was significantly increased compared to the linear form. Whereas the linear glucanase lost half of its activity after 3 min at 65 °C, the two circular variants have 6-fold (LicA-C1) and 16-fold (LicA-C2) increased half-life time of inactivation. In agreement with this, fluorescence spectroscopy and differential scanning calorimetry studies revealed that circular enzymes undergo structural changes at higher temperatures compared to that of the linear form. The effect of calcium on the conformational stability and function of the circular LicAs was also investigated, and we observed that the presence of calcium ions results in increased thermal stability. The impact of the length of the designed loops on thermal stability of the circular proteins is discussed, and it is suggested that cyclization may be an efficient strategy for the increased stability of proteins.

Hot Transcriptomics

DNA microarray technology allows for a quick and easy comparison of complete transcriptomes, resulting in improved molecular insight in fluctuations of gene expression. After emergence of the microarray technology about a decade ago, the technique has now matured and has become routine in many molecular biology laboratories. Numerous studies have been performed that have provided global transcription patterns of many organisms under a wide range of conditions. Initially, implementation of this high-throughput technology has lead to high expectations for ground breaking discoveries. Here an evaluation is performed of the insight that transcriptome analysis has brought about in the field of hyperthermophilic archaea. The examples that will be discussed have been selected on the basis of their impact, in terms of either biological insight or technological progress.