GroEL-GroES solubilizes abundantly expressed xylulokinase in Escherichia coli

Genetic analysis of D-xylose metabolism pathways in Gluconobacter oxydans 621H

D-xylose is one of the most abundant carbohydrates in nature. This work focuses on xylose metabolism of Gluconobacter oxydans as revealed by a few studies conducted to understand xylose utilization by this strain. Interestingly, the G. oxydans 621H Δmgdh strain (deficient in membrane-bound glucose dehydrogenase) was greatly inhibited when grown on xylose and no xylonate accumulation was observed in the medium. These experimental observations suggested that the mgdh gene was responsible for the conversion of xylose to xylonate in G. oxydans, which was also verified by whole-cell biotransformation. Since 621H Δmgdh could still grow on xylose in a very small way, two seemingly important genes in the oxo-reductive pathway for xylose metabolism, a xylitol dehydrogenase-encoding gox0865 (xdh) gene and a putative xylulose kinase-encoding gox2214 (xk) gene, were knocked out to investigate the effects of both genes on xylose metabolism. The results showed that the gox2214 gene was not involved in xylose metabolism, and there might be other genes encoding xylulose kinase. Though the gox0865 gene played a less important role in xylose metabolism compared to the mgdh gene, it was significant in xylitol utilization in G. oxydans, which meant that gox0865 was a necessary gene for the oxo-reductive pathway of xylose in vivo. To sum up, when xylose was used as the carbon source, the majority of xylose was directly oxidized to xylonate for further metabolism in G. oxydans, whereas only a minor part of xylose was metabolized by the oxo-reductive pathway.

The epitope for the polyol-responsive monoclonal antibody 8RB13 is in the flap-domain of the beta-subunit of bacterial RNA polymerase and can be used as an epitope tag for immunoaffinity chromatography

Polyol-responsive monoclonal antibodies (PR-mAbs) are useful for the purification of proteins in an easy, one step immunoaffinity step. These antibodies allow for gentle purification of proteins and protein complexes using a combination of a low molecular weight polyhydroxylated compound (polyol) and a nonchaotrophic salt in the eluting buffer. mAb 8RB13 has been characterized as one of these PR-mAbs and has been used to purify RNA polymerase from five species of bacteria. Here the epitope for 8RB13 has been identified as PEEKLLRAIFGEKAS, a sequence that is highly conserved in the β-subunit of bacterial RNA polymerase. This sequence is located in the "beta-flap" domain of RNA polymerase (and essentially comprises the "flap-tip helix"), an important binding site for sigma70. This location explains why only the core RNAP is purified using this mAb. This amino acid sequence has been developed into an epitope tag that can be used to purify a target protein from either bacterial or eukaryotic cells when genetically fused to a protein of interest.

A spectrophotometric assay for the determination of 4-diphosphocytidyl-2-C-methyl-D-erythritol kinase activity

We report an assay for the determination of the activity of 4-diphosphocytidyl-2-C-methyl-D-erythritol kinase, the enzyme which catalyzes the fourth reaction step of the 2-C-methyl-D-erythritol 4-phosphate pathway for the synthesis of isoprenoids, which is based on the spectrophotometrical determination of adenosine 5'-diphosphate using pyruvate kinase and L-lactate dehydrogenase as auxiliary enzymes. This method can be adapted to microtiter plates, can be automated, and because of its simplicity and speed can be useful for the functional characterization of the enzyme and for the screening of inhibitors with potential antibiotic or antimalarial action.