Advances and prospects of analytic methods for bacterial transglycosylation and inhibitor discovery.

The cell wall is essential for bacteria to maintain structural rigidity and withstand external osmotic pressure. In bacteria, the cell wall is composed of peptidoglycan. Lipid II is the basic unit for constructing highly cross-linked peptidoglycan scaffolds. Transglycosylase (TGase) is the initiating enzyme in peptidoglycan synthesis that catalyzes the ligation of lipid II moieties into repeating GlcNAc-MurNAc polysaccharides, followed by transpeptidation to generate cross-linked structures. In addition to the transglycosylases in the class-A penicillin-binding proteins (aPBPs), SEDS (shape, elongation, division and sporulation) proteins are also present in most bacteria and play vital roles in cell wall renewal, elongation, and division. In this review, we focus on the latest analytical methods including the use of radioactive labeling, gel electrophoresis, mass spectrometry, fluorescence labeling, probing undecaprenyl pyrophosphate, fluorescence anisotropy, ligand-binding-induced tryptophan fluorescence quenching, and surface plasmon resonance to evaluate TGase activity in cell wall formation. This review also covers the discovery of TGase inhibitors as potential antibacterial agents. We hope that this review will give readers a better understanding of the chemistry and basic research for the development of novel antibiotics.

Dual-targeting compounds possessing enhanced anticancer activity via microtubule disruption and histone deacetylase inhibition.

Dual-targeting anticancer agents 4-29 are designed by combining the structural features of purine-type microtubule-disrupting compounds and HDAC inhibitors. A library of the conjugate compounds connected by appropriate linkers was synthesized and found to possess HDACs inhibitory activity and render microtubule fragmentation by activating katanin, a microtubule-severing protein. Among various zinc-binding groups, hydroxamic acid shows the highest inhibitory activity of Class I HDACs, which was also reconfirmed by three-dimensional quantitative structure-activity relationship (3D-QSAR) pharmacophore prediction. The purine-hydroxamate conjugates exhibit enhanced cytotoxicity against MDA-MB231 breast cancer cells, H1975 lung cancer cells, and various clinical isolated non-small-cell lung cancer cells with different epidermal growth factor receptor (EGFR) status. Pyridyl substituents could be used to replace the C2 and N9 phenyl moieties in the purine-type scaffold, which can help to improve the solubility under physiological conditions, thus increasing cytotoxicity. In mice treated with the purine-hydroxamate conjugates, the tumor growth rate was significantly reduced without causing toxic effects. Our study demonstrates the potential of the dual-targeting purine-hydroxamate compounds for cancer monotherapy.

Effective assay of bacterial transglycosylation by molecular turn-on sensing and a second-order scattering effect.

Instead of using the lipid II substrate that requires prior labelling with a radioactive isotope or fluorophore to probe the formation of peptidoglycan in bacterial transglycosylation, the released undecaprenyl pyrophosphate (UPP) product is quantitatively measured either using a terpyridine-zinc fluorescence turn-on sensor or simply by the second-order scattering effect of the in situ formed UPP-calcium complex. Both the assay methods are utilized to identify moenomycin A as a potent transglycosylase inhibitor with a consistent IC50 value.

A Terpyridine Zinc Complex for Selective Detection of Lipid Pyrophosphates: A Model System for Monitoring Bacterial O- and N-Transglycosylations.

To develop an effective method for probing O- and N-glycosyltransfer reactions that are accompanied by the release of undecaprenyl pyrophosphate, solanesyl pyrophosphate (SPP) is used as a surrogate to bind a terpyridine zinc complex (Tpy-Zn), forming a fluorescent [Tpy-Zn]-SPP complex (Kass 106,000 M-1 in EtOH-CHCl3) with 5.8 µM LOD in HEPES buffer (10 mM, pH 7.4) containing 10 mM CaCl2 and 0.08% decyl PEG, which is similar to the bioassay conditions for lipid II polymerization.

A copper(ii)-dipicolylamine-coumarin sensor for maltosyltransferase assay.

A Cu(ii)-[di(2-methylpyridyl)methylamino]coumarin fluorescence turn-on sensor (Cu-1b) is designed to detect phosphate ions with Kass = 1.4 × 105 M-1 in HEPES buffer. Cu-1b is applied to probe the GlgE-catalyzed maltose-transfer reaction of α-maltose-1-phosphate to α-1,4-glucan with concomitant release of phosphate ions in Mycobacterium tuberculosis.