Tvp38, Tvp23, Tvp18 and Tvp15: novel membrane proteins in the Tlg2-containing Golgi/endosome compartments of Saccharomyces cerevisiae.
ABSTRACT Four previously uncharacterized proteins (Tvp38, Tvp23, Tvp18 and Tvp15) were found in Tlg2-containing membrane by proteomic analysis of immunoisolated Golgi subcompartments of Saccharomyces cerevisiae (Inadome et al., Mol. Cell. Biol., 25 (2005) 7696-7710). Immunofluorescence double staining of HA-tagged Tvp proteins and myc-tagged tSNAREs supported that these proteins mainly localize in the Tlg2-containing compartments. Conserved sequences of Tvp38, Tvp23 and Tvp18 are found in higher eukaryotes, but these homologues have not been characterized yet. All Tvp proteins were nonessential for growth under laboratory conditions. Immunoprecipitation of Tvp proteins indicated that Tvp23, Tvp18 and Tvp15 are in an interactive network with Yip1-family proteins, Yip4 and Yip5. They may collectively assist in the effective maintenance/function of the late Golgi/endosomal compartments. Disruptions of tvp15 and tvp23 showed synthetic aggravation with ypt6 or ric1 null mutation. Processing of carboxypeptidase Y and alkaline phosphatase in tvp disruptants occurred as in the wild type.
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ABSTRACT: Vesicle transfer processes in eukaryotes depend on specific proteins, which mediate the selective packing of cargo molecules for subsequent release out of the cells after vesicle fusion to the plasma membrane. The protein Tvp38 is conserved in yeasts and higher eukaryotes and potentially involved in vesicle transfer processes at the Golgi membrane. Members of the so-called "SNARE-associated proteins of the Tvp38-family" have also been identified in prokaryotes and those belong to the DedA protein family. Tvp38/DedA proteins are also conserved in cyanobacteria and chloroplasts. While only a single member of this family appears to be present in chloroplasts, cyanobacterial genomes typically encode multiple homologous proteins. Mainly based on our understanding of the DedA-homologous proteins of Escherichia coli, it appears likely that the function of these proteins in chloroplast and cyanobacteria involves stabilizing and organizing the structure of internal membrane systems.Frontiers in Plant Science 01/2013; 4:467. · 3.64 Impact Factor
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ABSTRACT: During cell wall biosynthesis, the Golgi apparatus is the platform for cell wall matrix biosynthesis and the site of packaging, of both matrix polysaccharides and proteins, into secretory vesicles with the correct targeting information. The objective of this study was to dissect the post-Golgi trafficking of cell wall polysaccharides using echidna as a vesicle traffic mutant of Arabidopsis thaliana and the pectin-secreting cells of the seed coat as a model system. ECHIDNA encodes a trans-Golgi network (TGN) localized protein, which was previously shown to be required for proper structure and function of the secretory pathway. In echidna mutants, some cell wall matrix polysaccharides accumulate inside cells, rather than being secreted to the apoplast. In this study, live cell imaging of fluorescent protein markers as well as transmission electron microscopy (TEM)/immunoTEM of cryofixed seed coat cells were used to examine the consequences of TGN disorganization in echidna mutants under conditions of high polysaccharide production and secretion. While in wild-type seed coat cells, pectin is secreted to the apical surface, in echidna, polysaccharides accumulate in post-Golgi vesicles, the central lytic vacuole, and ER-derived bodies. In contrast, proteins were partially mistargeted to internal multilamellar membranes in echidna. These results suggest that while secretion of cell wall polysaccharides and proteins at the TGN both require ECHIDNA, different vesicle trafficking components may mediate downstream events in their secretion from the TGN.Plant and Cell Physiology 09/2013; · 4.98 Impact Factor
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ABSTRACT: Bacterial resistance to antibiotics and biocides is an increasing public health problem. Genes belonging to the DedA family encoding integral membrane proteins are present in most bacterial genomes including Escherichia coli. An E. coli strain lacking partially redundant DedA family genes yqjA and yghB (strain BC202) displays temperature sensitivity and cell division defects. These phenotypes can be corrected by overexpression of mdfA, a Na(+)-K(+)/H(+) antiporter of the major facilitator superfamily. We show that BC202 is hypersensitive to several biocides and cationic compounds that are known substrates of several multidrug resistance transporters including MdfA, EmrE and AcrB. The introduction of deletions of genes encoding these drug transporters into BC202 results in additional sensitivity. Expression of wild type yghB or yqjA can restore drug resistance but this is eliminated upon mutation of two membrane-embedded acidic amino acids (E39 or D51 in either protein). This dependence upon membrane embedded acidic amino acids is a hallmark of proton-dependent antiporters. Overexpression of mdfA in BC202 or artificially restoring protonmotive force (PMF) restores wild type resistance to substrates of MdfA as well as other drug resistance transporters such as EmrE and AcrAB. These results suggest that YqjA and YghB may be membrane transporters required for PMF-dependent drug efflux in E. coli.Antimicrobial Agents and Chemotherapy 11/2013; · 4.57 Impact Factor