The Plant Exocyst

The exocyst is an octameric vesicle tethering complex that functions upstream of SNARE mediated exocytotic vesicle fusion with the plasma membrane. All proteins in the complex have been conserved during evolution, and genes that encode the exocyst subunits are present in the genomes of all plants investigated to date. Although the plant exocyst has not been studied in great detail, it is likely that the basic function of the exocyst in vesicle tethering is conserved. Nevertheless, genomic and genetic studie...     

The virtosome-a novel cytosolic informative entity and intercellular messenger

Studies on a range of prokaryote and eukaryote cells and tissues have shown that a newly synthesized DNA/RNA-lipoprotein complex is released in a regulated manner. This complex, termed a virtosome, is a novel cytosolic component of eukaryote cells. The released virtosomes can readily enter other cells where they can modify the biology of the recipient cells. Such modifications include immunological changes and transformation from normal to cancer cells. The virtosomes form a normal component of the circulating nucleic acids in plasma and serum currently used for clinical diagnostic purposes. Given the transformative powers of virtosomes released from tumour cells, the presence of such a complex in human plasma could readily offer the basis of an alternative mechanism for the initiation of metastases.     

The use of Listeria monocytogenes as a DNA delivery vector for cancer gene therapy

Listeria monocytogenes is an intracellular pathogen that lyses the phagosomal vacuole of infected cells, proliferates in the host cell cytoplasm and can actively enter adjacent cells. The pathogen is therefore well suited to exploitation as a vector for the delivery of DNA to target cells as the lifecycle favors cellular targeting with vector amplification and the potential for cell-to-cell spread. We have recently demonstrated DNA transfer by L. monocytogenes in growing tumors in murine models. Our approach exploited an ampicillin sensitive stain of L. monocytogenes which can be lysed through systemic administration of ampicillin to facilitate release of plasmid DNA for expression by infected mammalian cells. Here, we discuss the implications of this technology and the potential for future improvements of the system.     

M-cells: origin, morphology and role in mucosal immunity and microbial pathogenesis

M-cells are specialized cells found in the follicle-associated epithelium of intestinal Peyer's patches of gut-associated lymphoid tissue and in isolated lymphoid follicles, appendix and in mucosal-associated lymphoid tissue sites outside the gastrointestinal tract. In the gastrointestinal tract, M-cells play an important role in transport of antigen from the lumen of the small intestine to mucosal lymphoid tissues, where processing and initiation of immune responses occur. Thus, M-cells act as gateways to the mucosal immune system and this function has been exploited by many invading pathogens. Understanding the mechanism by which M-cells sample antigen will inform the design of oral vaccines with improved efficacy in priming mucosal and systemic immune responses. In this review, the origin and morphology of M-cells, and their role in mucosal immunity and pathogenesis of infections are discussed.     

Cadmium(II) complexes of the glycerophosphodiester-degrading enzyme GpdQ and a biomimetic N,O ligand

The glycerophosphodiester-degrading enzyme GpdQ from Enterobacter aerogenes is a promising bioremediator owing to its ability to degrade some organophosphate pesticides and diester products originating from the hydrolysis of nerve agents such as VX. Here, the cadmium derivative of GpdQ was prepared by reconstituting the apoenzyme. Catalytic measurements with (Cd²⁺)₂-GpdQ and the phosphodiester substrate bis(4-nitrophenyl)phosphate yield k _cat = 15 s⁻¹. The pK _a of 9.4, determined from the pH dependence of the catalytic activity, implicates a hydroxide ligand as the catalytic nucleophile. Also prepared was the cadmium-containing biomimetic [Cd₂((HP)₂B)(OAc)₂(OH₂)](PF₆) (where (HP)₂B is [2,6-bis([(2-pyridylmethyl)(2-hydroxyethyl)amino]methyl)-4-methylphenol]), which mimics the asymmetry of the metal ion coordination in the active site of GpdQ. The phosphoesterase-like activity of [Cd₂((HP)₂B)(OAc)₂(OH₂)](PF₆) was studied using the substrate bis(2,4-dinitrophenyl)phosphate, yielding a kinetically relevant pK _a of 8.9, with k _cat = 0.004 s⁻¹. In summary, the model is both an adequate structural and a reasonable functional mimic of GpdQ.     

The relationship between the activities of the pentose phosphate pathway and glycolysis during early stages of floral induction in spinach

A quantitative cytochemical study was made of fructokinase, glucokinase, and fructokinase (both PFK-ATP and PFK-PP + F-2:6-P) activities in shoot apices of 4-week old Spinacia oleracea. The rates of activity of these enzymes in the central zone of the shoot apex of plants kept on a short day regime were compared with those from plants transferred from a range of timing up to 24 h to a continuous light regime when floral induction occurred. A mechanism is suggested explaining how no measurable change in activities of the enzymes assayed could still account for the availability of adequate levels G-6-P as substrate for pentose pathway activity which is almost doubled early on in cells of the central zone of shoot apices induced to flower.