Concerted Action of Evolutionarily Ancient and Novel SNARE Complexes in Flowering-Plant Cytokinesis

Membrane vesicles delivered to the cell-division plane fuse with one another to form the partitioning membrane during plant cytokinesis, starting in the cell center. In Arabidopsis, this requires SNARE complexes involving the cytokinesis-specific Qa-SNARE KNOLLE. However, cytokinesis still occurs in knolle mutant embryos, suggesting contributions from KNOLLE-independent SNARE complexes. Here we show that Qa-SNARE SYP132, having counterparts in lower plants, functionally overlaps with the flowering plant-specific KNOLLE. SYP132 mutation causes cytokinesis defects, knolle syp132 double mutants consist of only one or a few multi-nucleate cells, and SYP132 has the same SNARE partners as KNOLLE. SYP132 and KNOLLE also have non-overlapping functions in secretion and in cellularization of the embryo-nourishing endosperm resulting from double fertilization unique to flowering plants. Evolutionarily ancient non-specialized SNARE complexes originating in algae were thus amended by the appearance of cytokinesis-specific SNARE complexes, meeting the high demand for membrane-fusion capacity during endosperm cellularization in angiosperms. In plant cytokinesis, SNARE complexes mediate vesicle fusion for partitioning membrane formation. Park et al. show that evolutionarily ancient Qa-SNARE SYP132 functionally overlaps with flowering plant- and cytokinesis-specific Qa-SNARE KNOLLE. KNOLLE acquisition may have been due to high demand for membrane-fusion capacity during endosperm cellularization in flowering plants

Endocytosis and secretion in trypanosomatid parasites - Tumultuous traffic in a pocket

Trypanosomatids are flagellated protozoan parasites of invertebrates, vertebrates and plants. Some species, found in the subtropics and tropics, cause chronic diseases in humans and domestic animals. The surface of the trypanosomatid provides a shield against environmental challenges, ligands for interaction with host cells, as well as receptors and transporters for the uptake of nutrients. Communication between the parasite and its environment is confined to the flagellar pocket, an invagination of the plasma membrane around the base of the flagellum. In this review, the authors discuss endocytosis, secretion and membrane trafficking in Trypanosoma and Leishmania

New outer membrane-associated protease of Escherichia coli K-12.

The gene for a new outer membrane-associated protease, designated OmpP, of Escherichia coli has been cloned and sequenced. The gene encodes a 315-residue precursor protein possessing a 23-residue signal sequence. Including conservative substitutions and omitting the signal peptides, OmpP is 87% identical to the outer membrane protease OmpT. OmpP possessed the same enzymatic activity as OmpT. Immuno-electron microscopy demonstrated the exposure of the protein at the cell surface. Digestion of intact cells with proteinase K removed 155 N-terminal residues of OmpP, while the C-terminal half remained protected. It is possible that much of this N-terminal part is cell surface exposed and carries the enzymatic activity. Synthesis of OmpP was found to be thermoregulated, as is the expression of ompT (i.e., there is a low rate of synthesis at low temperatures) and, in addition, was found to be controlled by the cyclic AMP system

The cysteine proteinase inhibitor Z-Phe-Ala-CHN2 alters cell morphology and cell division activity of Trypanosoma brucei bloodstream forms in vivo

BACKGROUND: Current chemotherapy of human African trypanosomiasis or sleeping sickness relies on drugs developed decades ago, some of which show toxic side effects. One promising line of research towards the development of novel anti-trypanosomal drugs are small-molecule inhibitors of Trypanosoma brucei cysteine proteinases. RESULTS: In this study, we demonstrate that treatment of T. brucei-infected mice with the inhibitor, carbobenzoxy-phenylalanyl-alanine-diazomethyl ketone (Z-Phe-Ala-CHN2), alters parasite morphology and inhibits cell division. Following daily intra-peritoneal administration of 250 mg kg(-1) of Z-Phe-Ala-CHN2 on days three and four post infection (p.i.), stumpy-like forms with enlarged lysosomes were evident by day five p.i. In addition, trypanosomes exposed to the inhibitor had a 65% greater protein content than those from control mice. Also, in contrast to the normal 16% of parasites containing two kinetoplasts--a hallmark of active mitosis, only 4% of trypanosomes exposed to the inhibitor were actively dividing, indicating cell cycle-arrest. CONCLUSION: We suggest that inhibition of endogenous cysteine proteinases by Z-Phe-Ala-CHN2 depletes the parasite of essential nutrients necessary for DNA synthesis, which in turn, prevents progression of the cell cycle. This arrest then triggers differentiation of the long-slender into short-stumpy forms