Insights into biological functions across species: examining the role of Rab proteins in YIP1 family function.
ABSTRACT The YIP1 family comprises an evolutionarily conserved group of membrane proteins, which share the ability to bind di-prenylated Rab proteins. The biochemical capability of YIP1 family proteins suggests a possible role in the cycle of physical localization of Rab proteins between their cognate membranes and the cytosol. YIP1 is essential for viability in yeast and a deletion of YIP1 can be rescued with the human homologue YIP1A. We have made use of this evolutionary conservation of function to generate a series of mutant alleles of YIP1 to investigate the biological role of Yip1p. Our findings indicate evidence for the participation of Yip1p in both Rab and COPII protein function; at present, we are not able to distinguish between the models that these roles represent, i.e. independent or dependent activities of Yip1p.
SourceAvailable from: Helen I Zgurskaya[Show abstract] [Hide abstract]
ABSTRACT: YknXYZ is the ATP-binding cassette export complex from Bacillus subtilis, where YknX is a membrane fusion protein, YknY is an ATPase, and YknZ is a permease. The yknXYZ genes are arranged into an operon that also includes yknW, encoding a membrane protein with four putative transmembrane segments. Previous studies suggested that the yknWXYZ operon belongs to the σ(w) regulon and protects cells from the endogenous toxin SDP (sporulation-delaying protein) encoded by sdpC. In this study, we investigated the composition and function of YknW and YknXYZ. We report that the yknWXYZ operon is constitutively expressed in growing B. subtilis cells independently from sdpC. Chemical cross-linking in vivo and copurification approaches established that YknX interacts with YknYZ, whereas YknW binds YknXYZ, indicating that all four proteins form a complex in vivo. The complex assembly is modulated by YknW but proceeds in the absence of SdpC. When overproduced alone, YknW provides partial protection against SDP toxin, but all four Ykn proteins are required for full protection against both endogenous and exogenous SDP. We conclude that YknWXYZ is an unusual four-component transporter with a role in the starvation-induced killing of B. subtilis cells.Journal of bacteriology 06/2012; 194(16):4386-94. DOI:10.1128/JB.00223-12 · 2.69 Impact Factor
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ABSTRACT: The secretion of cell wall polysaccharides through the trans-Golgi network (TGN) is required for plant cell elongation. However, the components mediating the post-Golgi secretion of pectin and hemicellulose, the two major cell wall polysaccharides, are largely unknown. We identified evolutionarily conserved YPT/RAB GTPase Interacting Protein 4a (YIP4a) and YIP4b (formerly YIP2), which form a TGN-localized complex with ECHIDNA (ECH) in Arabidopsis thaliana. The localization of YIP4 and ECH proteins at the TGN is interdependent and influences the localization of VHA-a1 and SYP61, which are key components of the TGN. YIP4a and YIP4b act redundantly, and the yip4a yip4b double mutants have a cell elongation defect. Genetic, biochemical, and cell biological analyses demonstrate that the ECH/YIP4 complex plays a key role in TGN-mediated secretion of pectin and hemicellulose to the cell wall in dark-grown hypocotyls and in secretory cells of the seed coat. In keeping with these observations, Fourier transform infrared microspectroscopy analysis revealed that the ech and yip4a yip4b mutants exhibit changes in their cell wall composition. Overall, our results reveal a TGN subdomain defined by ECH/YIP4 that is required for the secretion of pectin and hemicellulose and distinguishes the role of the TGN in secretion from its roles in endocytic and vacuolar trafficking.The Plant Cell 07/2013; DOI:10.1105/tpc.113.112482 · 9.58 Impact Factor
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ABSTRACT: BACKGROUND: Rab proteins constitute a large family of monomeric GTP-binding proteins that regulate intracellular vesicle transport. Several Rab proteins, including rab31, have been shown to affect cancer progression and are related with prognosis in various types of cancer including breast cancer. Recently, the gene encoding rab31 was found to be overexpressed in estrogen receptor-positive breast cancer tissue. In a previous study we found a significant association of high rab31 mRNA expression with poor prognosis in node-negative breast cancer patients. In the present study, we aimed to investigate the impact of rab31 (over)-expression on important aspects of tumor progression in vitro and in vivo. METHODS: Breast cancer cells displaying low (MDA-MB-231) or no (CAMA-1) endogenous rab31 expression were stably transfected with a rab31 expression plasmid. Batch-transfected cells as well as selected cell clones, expressing different levels of rab31 protein, were analyzed with regard to proliferation, cell adhesion, the invasive capacity of tumor cells, and in vivo in a xenograft tumor model. Polyclonal antibodies directed to recombinantly expressed rab31 were generated and protein expression analyzed by immunohistochemistry, Western blot analysis, and a newly developed sensitive ELISA. RESULTS: Elevated rab31 protein levels were associated with enhanced proliferation of breast cancer cells. Interestingly, weak to moderate overexpression of rab31 in cell lines with no detectable endogenous rab31 expression was already sufficient to elicit distinct effects on cell proliferation. By contrast, increased expression of rab31 in breast cancer cells led to reduced adhesion towards several extracellular matrix proteins and decreased invasive capacity through MatrigelTM. Again, the rab31-mediated effects on cell adhesion and invasion were dose-dependent. Finally, in a xenograft mouse model, we observed a significantly impaired metastatic dissemination of rab31 overexpressing MDA-MB-231 breast cancer cells to the lung. CONCLUSIONS: Overexpression of rab31 in breast cancer cells leads to a switch from an invasive to a proliferative phenotype as indicated by an increased cell proliferation, reduced adhesion and invasion in vitro, and a reduced capacity to form lung metastases in vivo.Molecular Cancer 08/2012; 11(1):62. DOI:10.1186/1476-4598-11-62 · 5.40 Impact Factor