Defects in the human protein TMEM165 are known to cause a subtype of Congenital Disorders of Glycosylation. Transmembrane protein 165 (TMEM165) belongs to an uncharacterized family of membrane proteins called Uncharacterized Protein Family 0016, which are well conserved throughout evolution and share characteristics reminiscent of the cation/Ca 2+ exchanger superfamily. Gcr1 dependent translation factor 1 (Gdt1p), the budding yeast member of this family, contributes to Ca 2+ homeostasis via an uncharacterized Ca 2+ transport pathway localized in the Golgi apparatus. The gdt1Δ mutant was found to be sensitive to high concentrations of Ca 2+ , and interestingly, this sensitivity was suppressed by expression of TMEM165, the human ortholog of Gdt1p, indicating conservation of function among the members of this family. Patch-clamp analyses on human cells indicated that TMEM165 expression is linked to Ca 2+ ion transport. Furthermore, defects in TMEM165 affected both Ca 2+ and pH homeostasis. Based on these results, we propose that Gdt1p and TMEM165 could be members of a unique family of Golgi-localized Ca 2+ /H + antiporters and that modification of the Golgi Ca 2+ and pH balance could explain the glycosylation defects observed in TMEM165-deficient patients. CDGs are a family of inborn metabolic diseases affecting the glycosylation pathway. Most of these mutations are found in genes directly involved in glycosylation, however unique types of CDG have been found to be caused by deficiencies in vesicular Golgi trafficking (2-6) and Golgi pH homeostasis (7). TMEM165 belongs to a well-conserved, but uncharacterized, family of membrane proteins named UPF0016 (Uncharacterized Protein Family 0016; Pfam PF01169) and is localized in the Golgi apparatus (1). The members of this family are well conserved and are found in many organisms-for example, 919 different species of bacteria and 409 different eukaryotes.Gcr1 dependent translation factor 1 (Gdt1p) the yeast ortholog of TMEM165, is a 280-residue membrane protein and is involved in tolerance to high concentrations of calcium (Ca 2+ ) (8). In eukaryotic cells, Ca 2+ is a ubiquitous intracellular messenger involved in many different biological processes (9). To allow the increases in cytosolic calcium concentration ([Ca 2+ ] cyt ) required for these signaling mechanisms, it is absolutely necessary that the resting Ca 2+ levels are maintained below a certain threshold. Under normal conditions, the yeast [Ca 2+ ] cyt is maintained between 50 and 200 nM (10). The maintenance of this basal level and the return to normal levels after stimulation are achieved by a series of Ca 2+ pumps and exchangers located in different compartments of the cell: Pmr1p, the P-type Ca 2+ / Mn 2+ -ATPase localized in the medial-Golgi apparatus and responsible for the Ca 2+ supply for the secretory pathway (11-13), and Pmc1p (14), a P-type Ca 2+ -ATPase, and Vcx1p (15, 16), a Ca 2+ /H + exchanger (CAX), both responsible for the uptake of Ca 2+ through the vacuolar membrane.Yeast is a simple and conv...

SummaryThe cloning of abiotic stress-inducible genes from the moss Physcomitrella patens led to the identification of the gene PpTSPO1, encoding a protein homologous to the mammalian mitochondrial peripheral-type benzodiazepine receptor and the bacterial tryptophane-rich sensory protein. This class of proteins is involved in the transport of intermediates of the tetrapyrrole biosynthesis pathway. Like the mammalian homologue, the PpTSPO1 protein is localized to mitochondria. The generation of PpTSPO1-targeted moss knock-out lines revealed an essential function of the gene in abiotic stress adaptation. Under stress conditions, the PpTSPO1 null mutants show elevated H 2 O 2 levels, enhanced lipid peroxidation and cell death, indicating an important role of PpTSPO1 in redox homeostasis. We hypothesize that PpTSPO1 acts to direct porphyrin precursors to the mitochondria for heme formation, and is involved in the removal of photoreactive tetrapyrrole intermediates.

FtsZ is a filament-forming protein that assembles into a ring at the division site of prokaryotic cells. As FtsZ and tubulin share several biochemical and structural similarities, FtsZ is regarded as the ancestor of tubulin. Chloroplasts-the descendants of endosymbiotic bacteria within plant cells-also harbour FtsZ. In contrast to eubacteria, plants have several different FtsZ isoforms. So far, these isoforms have only been implicated with filamentous structures, rings and networks, inside chloroplasts. Here, we demonstrate that a novel FtsZ isoform in the moss Physcomitrella patens is located not only in chloroplasts but also in the cytoplasm, assembling into rings in both cell compartments. These findings comprise the first report on cytosolic localization of a eukaryotic FtsZ isoform, and indicate that this protein might connect cell and organelle division at least in moss.

Summary• Plant filamentous temperature-sensitive Z (FtsZ) proteins have been reported to be involved in biological processes related to plastids. However, the precise functions of distinct isoforms are still elusive. Here, the intracellular localization of the FtsZ1-1 isoform in a moss, Physcomitrella patens , was examined. Furthermore, the in vivo interaction behaviour of four distinct FtsZ isoforms was investigated.• Localization studies of green fluorescent protein (GFP)-tagged FtsZ1-1 and fluorescence resonance energy transfer (FRET) analyses employing all dual combinations of four FtsZ isoforms were performed in transient protoplast transformation assays.• FtsZ1-1 is localized to network structures inside the chloroplasts and exerts influence on plastid division. Interactions between FtsZ isoforms occur in distinct ordered structures in the chloroplasts as well as in the cytosol.• The results expand the view of the involvement of Physcomitrella FtsZ proteins in chloroplast and cell division. It is concluded that duplication and diversification of ftsZ genes during plant evolution were the main prerequisites for the successful remodelling and integration of the prokaryotic FtsZ-dependent division mechanism into the cellular machineries of distinct complex processes in plants.