Hypothetical Protein BPSL3393 of Burkholderia pseudomallei is Involved in Ethanolamine Catabolism.

Burkholderia pseudomallei is a soil-dwelling bacterium that causes a globally emerging disease called melioidosis. Approximately one third of the in silico annotated genes in its genome are classified as hypothetical genes. This group of genes is difficult to be functionally characterised partly due to the absence of noticeable phenotypes under conventional laboratory settings. A bioinformatic survey of hypothetical genes revealed a gene designated as BPSL3393 that putatively encodes a small protein of 11 kDA with a CoA binding domain. BPSL3393 is conserved in all the B. pseudomallei genomes as well as various in other species within the genus Burkholderia. Taking into consideration that CoA plays a ubiquitous metabolic role in all life forms, characterisation of BPSL3393 may uncover a previously over-looked metabolic feature of B. pseudomallei. The gene was deleted from the genome using a double homologous recombination approach yielding a null mutant. The BPSL3393 mutant showed no difference in growth rate with the wild type under rich and minimal growth conditions. An extensive metabolic phenotyping test was performed involving 95 metabolic substrates. The deletion mutant of BPSL3393 was severely impaired in its ethanolamine metabolism. The growth rate of the mutant was attenuated when ethanolamine was used as the sole carbon source. A transcriptional analysis of the ethanolamine metabolism genes showed that they were down-regulated in the BPSL3393 mutant. This seemed to suggest that BPSL3393 functions as a positive regulator for ethanolamine metabolism.

Prediction of recombinant protein overexpression in Escherichia coli using a machine learning based model (RPOLP).

Recombinant protein overexpression, an important biotechnological process, is ruled by complex biological rules which are mostly unknown, is in need of an intelligent algorithm so as to avoid resource-intensive lab-based trial and error experiments in order to determine the expression level of the recombinant protein. The purpose of this study is to propose a predictive model to estimate the level of recombinant protein overexpression for the first time in the literature using a machine learning approach based on the sequence, expression vector, and expression host. The expression host was confined to Escherichia coli which is the most popular bacterial host to overexpress recombinant proteins. To provide a handle to the problem, the overexpression level was categorized as low, medium and high. A set of features which were likely to affect the overexpression level was generated based on the known facts (e.g. gene length) and knowledge gathered from related literature. Then, a representative sub-set of features generated in the previous objective was determined using feature selection techniques. Finally a predictive model was developed using random forest classifier which was able to adequately classify the multi-class imbalanced small dataset constructed. The result showed that the predictive model provided a promising accuracy of 80% on average, in estimating the overexpression level of a recombinant protein.

Validation of a Burkholderia pseudomallei hypothetical protein and determination of its translational start codon using chromosomal integration of His-Tag coding sequence.

In this post genomic era, there are a great number of in silico annotated hypothetical genes. However, experimental validation of the functionality of these genes remains tentative. Two of the major challenges faced by researcher are whether these hypothetical genes are protein-coding genes and whether their corresponding predicted translational start codons are correct. In this report, we demonstrate a convenient procedure to validate the presence of a hypothetical gene product of BPSS1356 from Burkholderia pseudomallei as well as its start codon. It was done by integration of a His-Tag coding sequence into C-terminal end of BPSS1356 gene via homologous recombination. We then purified the native protein using affinity chromatography. The genuine start codon of BPSS1356 was then determined by protein N-terminal sequencing.

Cloning and characterization of poly(3-hydroxybutyrate) biosynthesis genes from Pseudomonas sp. USM 4-55.

Pseudomonas sp. USM 4-55 is a locally isolated bacterium that possesses the ability to produce polyhydroxyalkanoates (PHA) consisting of both poly(3-hydroxybutyrate) [P(3HB)] homopolymer and medium-chain length (mcl) monomers (6 to 14 carbon atoms) when sugars or fatty acids are utilized as the sole carbon source. In this study, the P(3HB) biosynthesis operon carrying the phbC(Ps) P(3HB) synthase was successfully cloned and sequenced using a homologous probe. Three open reading frames encoding NADPH-dependent acetoacetyl-coenzyme A reductase (PhbB(Ps)), beta-ketothiolase (PhbA(Ps)) and P(3HB) synthase (PhbC(Ps)) were found in the phb operon. The genetic organization of phb operon showed a putative promoter region, followed by phbB(Ps)-phbA(Ps)-phbC(Ps). phbR(Ps)which encoded a putative transcriptional activator was located in the opposite orientation, upstream of phbBAC(Ps). Heterologous expression of pGEM''ABex harboring phbC(Ps) in Escherichia coli JM109 resulted in P(3HB) accumulation of up to 40% of dry cell weight (DCW).

An atypical catalytic mechanism involving three cysteines of thioredoxin.

Unlike other thioredoxins h characterized so far, a poplar thioredoxin of the h type, PtTrxh4, is reduced by glutathione and glutaredoxin (Grx) but not NADPH:thioredoxin reductase (NTR). PtTrxh4 contains three cysteines: one localized in an N-terminal extension (Cys(4)) and two (Cys(58) and Cys(61)) in the classical thioredoxin active site ((57)WCGPC(61)). The property of a mutant in which Cys(58) was replaced by serine demonstrates that it is responsible for the initial nucleophilic attack during the catalytic cycle. The observation that the C4S mutant is inactive in the presence of Grx but fully active when dithiothreitol is used as a reductant indicates that Cys(4) is required for the regeneration of PtTrxh4 by Grx. Biochemical and x-ray crystallographic studies indicate that two intramolecular disulfide bonds involving Cys(58) can be formed, linking it to either Cys(61) or Cys(4). We propose thus a four-step disulfide cascade mechanism involving the transient glutathionylation of Cys(4) to convert this atypical thioredoxin h back to its active reduced form.

Scaffolds from electrospun polyhydroxyalkanoate copolymers: fabrication, characterization, bioabsorption and tissue response.

Polyhydroxyalkanoate (PHA) copolymers of poly[(R)-3-hydroxybutyrate-co-5mol%-(R)-3-hydroxyhexanoate], poly[(R)-3-hydroxybutyrate-co-7mol%-4-hydroxybutyrate] and poly[(R)-3-hydroxybutyrate-co-97mol%-4-hydroxybutyrate] were electrospun to fabricate scaffolds with enhanced biocompatibility and bioabsorption. Subcutaneous implantation of the fibers in rats was performed to investigate their bioabsorption behavior and tissue response. The fibers before and after the in vivo experiments were characterized using gel permeation chromatography, scanning electron microscopy, X-ray diffraction and tensile test. Histological evaluation was also performed to determine the tissue response. The structures and properties of the electrospun PHA copolymers were compared with those of the electrospun poly[(R)-3-hydroxybutyrate]. The content and type of the second monomer and the diameter of fiber significantly influence the bioabsorption. The tissue response was found to improve with the high content of 4-hydroxybutyrate.