Phage-choline Kinase Inhibitor Combination to Control Pseudomonas aeruginosa: A Promising Combo.

BACKGROUND: Pseudomonas aeruginosa is one of the most prevalent opportunistic pathogens in humans that has thrived and proved to be difficult to control in this "post-antibiotic era." Antibiotic alternatives are necessary for fighting against this resilient bacterium. Even though phages might not be "the wonder drug" that solves everything, they still provide a viable option to combat P. aeruginosa and curb the threat it imposes. MAIN FINDINGS: The combination of antibiotics with phages, however, poses a propitious treatment option for P. aeruginosa. Choline kinase (ChoK) is the enzyme that synthesizes phosphorylcholine subsequently incorporated into lipopolysaccharide located at the outer membrane of gram-negative bacteria. Recently, inhibition of ChoKs has been proposed as a promising antibacterial strategy. Successful docking of Hemicholinium-3, a choline kinase inhibitor, to the model structure of P. aeruginosa ChoK also supports the use of this inhibitor or its derivatives to inhibit the growth of this microorganism. CONCLUSION: Therefore, the combination of the novel antimicrobial "choline kinase inhibitors (ChoKIs)" with a phage cocktail or synthetic phages as a potential treatment for P. aeruginosa infection has been proposed.

Klebsiella pneumoniae yggG gene product: a zinc-dependent metalloprotease.

Klebsiella pneumoniae causes neonatal sepsis and nosocomial infections. One of the strains, K. pneumoniae MGH 78578, shows high level of resistance to multiple microbial agents. In this study, domain family, amino acid sequence and topology analyses were performed on one of its hypothetical protein, YggG (KPN_03358). Structural bioinformatics approaches were used to predict the structure and functionality of YggG protein. The open reading frame (ORF) of yggG, which was a putative metalloprotease gene, was also cloned, expressed and characterized. The ORF was PCR amplified from K. pneumoniae MGH 78578 genomic DNA and cloned into a pET14-b vector for heterologous expression in Escherichia coli. The purified YggG protein was subsequently assayed for casein hydrolysis under different conditions. This protein was classified as peptidase M48 family and subclan gluzincin. It was predicted to contain one transmembrane domain by TMpred. Optimal protein expression was achieved by induction with 0.6 mM isopropyl thiogalactoside (IPTG) at 25 °C for six hours. YggG was purified as soluble protein and confirmed to be proteolytically active under the presence of 1.25 mM zinc acetate and showed optimum activity at 37 °C and pH 7.4. We confirmed for the first time that the yggG gene product is a zinc-dependent metalloprotease.

MicroRNA-367-3p induces apoptosis and suppresses migration of MCF-7 cells by downregulating the expression of human choline kinase α.

Choline kinase (ChK) catalyzes the first step in the CDP-choline pathway for the synthesis of phosphatidylcholine. The α isoform of this enzyme is overexpressed in various types of cancer and its inhibition or downregulation has been applied as an anticancer strategy. In spite of increasing attention being paid to ChK expression, as well as its activity and inhibition in cancer, there are only limited studies available on the regulation of ChK, including its regulation by microRNAs (miRNAs/miRs). The dysregulation of gene expression by miRNAs is a common cause for carcinogenesis. In the present study, miR-367-3p was predicted to target the 3'-untranslated region (UTR) of the ChK α (chka) mRNA transcript. The binding of miR-367-3p to the 3'-UTR of chka was validated by a luciferase assay. The effects of the miR-367-3p mimic on chka gene and protein expression levels were determined by reverse transcription-quantitative polymerase chain reaction and western blot analysis, respectively. miR-367-3p significantly downregulated the expression of chka to ~60% of the negative control. Cells transfected with miR-367-3p exhibited higher levels of apoptosis and a lower cell migration compared with the control. To the best of our knowledge, the present study provided the first experimental evidence of the regulation of chka expression by miR-367-3p. The pro-apoptotic and suppressive effects of miR-367-3p on cell migration were similar to the anticancer effects resulting from the inhibition of ChK enzyme activity or the knockdown of chka gene expression by small interfering RNA. Therefore, these findings may potentially lead to the use of miR-367-3p in anticancer strategies that target ChK.

Elucidation of human choline kinase crystal structures in complex with the products ADP or phosphocholine.

Choline kinase, responsible for the phosphorylation of choline to phosphocholine as the first step of the CDP-choline pathway for the biosynthesis of phosphatidylcholine, has been recognized as a new target for anticancer therapy. Crystal structures of human choline kinase in its apo, ADP and phosphocholine-bound complexes, respectively, reveal the molecular details of the substrate binding sites. ATP binds in a cavity where residues from both the N and C-terminal lobes contribute to form a cleft, while the choline-binding site constitutes a deep hydrophobic groove in the C-terminal domain with a rim composed of negatively charged residues. Upon binding of choline, the enzyme undergoes conformational changes independently affecting the N-terminal domain and the ATP-binding loop. From this structural analysis and comparison with other kinases, and from mutagenesis data on the homologous Caenorhabditis elegans choline kinase, a model of the ternary ADP.phosphocholine complex was built that reveals the molecular basis for the phosphoryl transfer activity of this enzyme.

Highly specific antibodies for co-detection of human choline kinase α1 and α2 isoforms.

BACKGROUND: Choline kinase is the first enzyme in the CDP-choline pathway that synthesizes phosphatidylcholine, the major phospholipid in eukaryotic cell membranes. In humans, choline kinase exists as three isoforms (CKα1, α2, and ß). Specific inhibition of CKα has been reported to selectively kill tumoral cells. Monoclonal and polyclonal antibodies against CKα used in previous studies to detect the level of this isozyme in different cellular or biochemical contexts were able to detect either the α1 or the α2 isoform. METHODOLOGY/PRINCIPAL FINDINGS: In this study, an antiserum against CKα was produced by immunizing rabbits with denatured, purified recombinant CKα2 full-length protein. This antiserum was highly specific for CKα when tested with extracts from different cell lines, and there was no cross reactivity with purified CKß and other related proteins like human ethanolamine kinases (EK) and yeast choline or ethanolamine kinases. The antiserum simultaneously detected both CKα1 and α2 isoforms in MCF-7 and HepG2 cell extracts, but not in HeLa, HCT-116, and mouse embryonic stem cell extracts. Subsequent protein dot blot assay of total CKα in a human normal/tumor protein array of 30 tissue samples by using the antiserum showed that CKα was not overexpressed in all tumor tissues when compared to their normal counterparts. Most striking differences between tumor and normal CKα expression levels were observed in kidney (11-fold higher in tumor) and liver (15-fold lower in tumor) samples. CONCLUSION/SIGNIFICANCE: Apart from its high sensitivity and specificity, the antiserum produced in this work, which does not require further purification, has the advantage of co-detecting both α1 and α2 isoforms in cell extracts for direct comparison of their expression levels.