Complexity of Hsp90 in organelle targeting

Laboratory of Molecular Biology, Agricultural Biotechnology Department, Agricultural University of Athens, Athens, Greece.
Plant Molecular Biology (Impact Factor: 4.26). 08/2008; 67(4):323-34. DOI: 10.1007/s11103-008-9322-8
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Heat shock protein 90 (Hsp90) is an abundant and highly conserved molecular chaperone. In Arabidopsis, the Hsp90 gene family consists of seven members. Here, we report that the AtHsp90-6 gene gives rise to two mRNA populations, termed AtHsp90-6L and AtHsp90-6S due to alternative initiation of transcription. The AtHsp90-6L and AtHsp90-6S transcription start sites are located 228 nucleotides upstream and 124 nucleotides downstream of the annotated translation start site, respectively. Both transcripts are detected under normal or heat-shock conditions. The inducibility of AtHsp90-6 mRNAs by heat shock implies a potential role of both isoforms in stress management. Stable transformation experiments with fusion constructs between the N-terminal part of each AtHsp90-6 isoform and green fluorescent protein indicated import of both fusion proteins into mitochondria. In planta investigation confirmed that fusion of the AtHsp90-5 N-terminus to green fluorescent protein (GFP) did result in specific chloroplastic localization. The mechanisms of regulation for mitochondria- and plastid-localized chaperone-encoding genes are not well understood. Future work is needed to address the possible roles of harsh environmental conditions and developmental processes on fine-tuning and compartmentalization of the AtHsp90-6L, AtHsp90-6S, and AtHsp90-5 proteins in Arabidopsis.

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Available from: Kosmas Haralampidis, Sep 09, 2014
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    • "Heat shock proteins (HSPs) that first described in Drosophila melanogaster [1], are evolutionarily conserved protein families which are ubiquitous in all eukaryotic organisms. HSPs are essential for cells under both normal and stressed conditions as they participate in diverse processes ranging from cellular homeostasis and signal transduction to development [2]. In addition, HSPs also play key roles in defense responses against various environmental stresses that could potentially damage the cellular and molecular structures in the cells [3]. "
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    ABSTRACT: Heat shock protein 90 (HSP90), a highly conserved molecular chaperone, plays essential roles in folding, keeping structural integrity, and regulating the subset of cytosolic proteins. We cloned the cDNA of Chlorella vulgaris HSP90 (named CvHSP90) by combining homology cloning with rapid amplification of cDNA ends (RACE). Sequence analysis indicated that CvHSP90 is a cytosolic member of the HSP90 family. Quantitative RT-PCR was applied to determine the expression level of messenger RNA (mRNA) in CvHSP90 under different stress conditions. C. vulgaris was kept in different temperatures (5-45°C) for 1 h. The mRNA expression level of CvHSP90 increased with temperature from 5 to 10°C, went further from 35 to 40°C, and reached the maximum at 40°C. On the other hand, for C. vulgaris kept at 35°C for different durations, the mRNA expression level of CvHSP90 increased gradually and reached the peak at 7 h and then declined progressively. In addition, the expression level of CvHSP90 at 40 or 45 in salinity (‰) was almost fourfold of that at 25 in salinity (‰) for 2 h. Therefore, CvHSP90 may be a potential biomarker to monitor environment changes.
    03/2014; 2014:487050. DOI:10.1155/2014/487050
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    • "These include an involvement in glycolysis (Plaxton, 1996), the oxidative branch of the pentose phosphate pathway (Schnarrenberger et al., 1995), protein biosynthesis and degradation (Bailey-Serres et al., 2009; Vierstra, 2009), signal transduction (Lecourieux et al., 2006; Klimecka and Muszynska, 2007), primary and secondary metabolite biosynthesis and transportation (Lundmark et al., 2006; Lunn, 2007; Martinoia et al., 2007; Weber and Fischer, 2007; Krueger et al., 2009), stress response signaling (Yamada and Nishimura, 2008; Cazale et al., 2009; Sugio et al., 2009), and the accumulation of enzymes for defense and detoxification (Laule et al., 2003; Dixon et al., 2009; Sappl et al., 2009). Furthermore, nuclearencoded organellar proteins are synthesized in the cytosol prior to their import into organelles by targeting peptides (Jarvis, 2008; Prassinos et al., 2008; Huang et al., 2009). Although the cytosol has a multitude of prominent biochemical processes in the eukaryotic cell (Figure 1), only two proteome surveys have been carried to date on the plant cytosol. "
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    ABSTRACT: The plant cytosol is the major intracellular fluid that acts as the medium for inter-organellar crosstalk and where a plethora of important biological reactions take place. These include its involvement in protein synthesis and degradation, stress response signaling, carbon metabolism, biosynthesis of secondary metabolites, and accumulation of enzymes for defense and detoxification. This central role is highlighted by estimates indicating that the majority of eukaryotic proteins are cytosolic. Arabidopsis thaliana has been the subject of numerous proteomic studies on its different subcellular compartments. However, a detailed study of enriched cytosolic fractions from Arabidopsis cell culture has been performed only recently, with over 1,000 proteins reproducibly identified by mass spectrometry. The number of proteins allocated to the cytosol nearly doubles to 1,802 if a series of targeted proteomic characterizations of complexes is included. Despite this, few groups are currently applying advanced proteomic approaches to this important metabolic space. This review will highlight the current state of the Arabidopsis cytosolic proteome since its initial characterization a few years ago.
    Frontiers in Plant Science 02/2014; 5:21. DOI:10.3389/fpls.2014.00021 · 3.95 Impact Factor
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    • "As shown in Figure 3A, the fluorescent signal of PtHsp90-3-YFP is also detected both in the nucleus and in the cytoplasm. This is consistent with the subcellular localizations of cytoplasmic Arabidopsis Hsp90 proteins [4,15]. Using the autofluorescence of chlorophyll as a marker, we found that the fluorescent signals of both PtHsp90-5a-YFP and PtHsp90-5b-YFP are well co-localized with red chlorophyll autofluorescence (Figure 3B and 3C). "
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    ABSTRACT: Members of the heat shock protein 90 (Hsp90) class of proteins are evolutionarily conserved molecular chaperones. They are involved in protein folding, assembly, stabilization, activation, and degradation in many normal cellular processes and under stress conditions. Unlike many other well-characterized molecular chaperones, Hsp90s play key roles in signal transduction, cell-cycle control, genomic silencing, and protein trafficking. However, no systematic analysis of genome organization, gene structure, and expression compendium has been performed in the Populus model tree genus to date. We performed a comprehensive analysis of the Populus Hsp90 gene family and identified 10 Populus Hsp90 genes, which were phylogenetically clustered into two major groups. Gene structure and motif composition are relatively conserved in each group. In Populus trichocarpa, we identified three paralogous pairs, among which the PtHsp90-5a/PtHsp90-5b paralogous pair might be created by duplication of a genome segment. Subcellular localization analysis shows that PtHsp90 members are localized in different subcellular compartments. PtHsp90-3 is localized both in the nucleus and in the cytoplasm, PtHsp90-5a and PtHsp90-5b are in chloroplasts, and PtHsp90-7 is in the endoplasmic reticulum (ER). Furthermore, microarray and semi-quantitative real-time RT-PCR analyses show that a number of Populus Hsp90 genes are differentially expressed upon exposure to various stresses. The gene structure and motif composition of PtHsp90s are highly conserved among group members, suggesting that members of the same group may also have conserved functions. Microarray and RT-PCR analyses show that most PtHsp90s were induced by various stresses, including heat stress. Collectively, these observations lay the foundation for future efforts to unravel the biological roles of PtHsp90 genes.
    BMC Genomics 08/2013; 14(1):532. DOI:10.1186/1471-2164-14-532 · 3.99 Impact Factor
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