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Multi-subunit Complexes (multi-subunit + complex)
Selected AbstractsThe nuclear gene HCF107 encodes a membrane-associated R-TPR (RNA tetratricopeptide repeat)-containing protein involved in expression of the plastidial psbH gene in ArabidopsisTHE PLANT JOURNAL, Issue 5 2005Aniruddha P. Sane Summary Expression of the genes of plastidial psbB operon (psbB-psbT-psbH-petB-petD) involves multiple processing events and formation of several mono-, di- and multi-cistronic transcripts which are further regulated by differential stability and expression. Here we describe the identification of the HCF107 gene that is involved in the 5,-end processing/stability and/or translation of the psbH gene and in the translation of the psbB gene. HCF107 is an RNA-TPR-containing protein with 11 RTPRs that are tandemly arranged. A single mutation in the third RTPR that changes a conserved alanine residue to a threonine affects both 5,-end-processed psbH transcript accumulation as well as psbB translation, resulting in disruption of PSII and seedling lethal plants. The protein is localized to the plastid membranes and is present as part of a multi-subunit complex in the range of 60,190 and 600,800 kDa. HCF107 thus represents a new member of the growing helical repeat family of proteins that seem to play a gene-specific role in regulating plastidial gene expression and biogenesis. [source] Molecular determinants of ligand specificity in family 11 carbohydrate binding modules , an NMR, X-ray crystallography and computational chemistry approachFEBS JOURNAL, Issue 10 2008Aldino Viegas The direct conversion of plant cell wall polysaccharides into soluble sugars is one of the most important reactions on earth, and is performed by certain microorganisms such as Clostridium thermocellum (Ct). These organisms produce extracellular multi-subunit complexes (i.e. cellulosomes) comprising a consortium of enzymes, which contain noncatalytic carbohydrate-binding modules (CBM) that increase the activity of the catalytic module. In the present study, we describe a combined approach by X-ray crystallography, NMR and computational chemistry that aimed to gain further insight into the binding mode of different carbohydrates (cellobiose, cellotetraose and cellohexaose) to the binding pocket of the family 11 CBM. The crystal structure of C. thermocellum CBM11 has been resolved to 1.98 Å in the apo form. Since the structure with a bound substrate could not be obtained, computational studies with cellobiose, cellotetraose and cellohexaose were carried out to determine the molecular recognition of glucose polymers by CtCBM11. These studies revealed a specificity area at the CtCBM11 binding cleft, which is lined with several aspartate residues. In addition, a cluster of aromatic residues was found to be important for guiding and packing of the polysaccharide. The binding cleft of CtCBM11 interacts more strongly with the central glucose units of cellotetraose and cellohexaose, mainly through interactions with the sugar units at positions 2 and 6. This model of binding is supported by saturation transfer difference NMR experiments and linebroadening NMR studies. [source] Expression of multiple AQP4 pools in the plasma membrane and their association with the dystrophin complexJOURNAL OF NEUROCHEMISTRY, Issue 6 2008Grazia Paola Nicchia Abstract Altered aquaporin-4 (AQP4) expression has been reported in brain edema, tumors, muscular dystrophy, and neuromyelitis optica. However, the plasma membrane organization of AQP4 and its interaction with proteins such as the dystrophin-associated protein complex are not well understood. In this study, we used sucrose density gradient ultracentrifugation and 2D blue native/sodium dodecyl sulfate,polyacrylamide gel electrophoresis and showed the expression of several AQP4 multi-subunit complexes (pools) of different sizes, ranging from , 1 MDa to ,500 kDa and containing different ratios of the 30/32 kDa AQP4 isoforms, indicative of orthogonal arrays of particles of various sizes. A high molecular weight pool co-purified with dystrophin and ,-dystroglycan and was drastically reduced in the skeletal muscle of mdx3cv mice, which have no dystrophin. The number and size of the AQP4 pools were the same in the kidney where dystrophin is not expressed, suggesting the presence of dystrophin-like proteins for their expression. We found that AQP2 is expressed only in one major pool of ,500 kDa, indicating that the presence of different pools is a peculiarity of AQP4 rather than a widespread feature in the AQP family. Finally, in skeletal muscle caveolin-3 did not co-purify with any AQP4 pool, indicating the absence of interaction of the two proteins and confirming that caveolae and orthogonal arrays of particles are two independent plasma membrane microdomains. These results contribute to a better understanding of AQP4 membrane organization and raise the possibility that abnormal expression of specific AQP4 pools may be found in pathological states. [source] Cell cycle-related variation in subcellular localization of eIF3e/INT6 in human fibroblastsCELL PROLIFERATION, Issue 2 2004S. J. Watkins In addition, the protein can interact with two other multi-subunit complexes: the COP9 signalosome (CSN) and the proteasome. The role of INT6 in tumourigenesis is nonetheless currently unclear. Here, using immunofluorescence microscopy, we show that eIF3e/INT6 is localized in part to the nucleus, while other eIF3 components are cytoplasmic. Primary human fibroblasts, but not their transformed counterparts, showed reduced nuclear INT6 staining in some cells, and this reduction was maximal in early S phase. This variation in eIF3e/INT6 may indicate regulated shuttling between cellular compartments and would be consistent with the presence of a nuclear export signal as well as a nuclear localization signal in the protein sequence. Loss of regulation of eIF3e/INT6 redistribution may therefore be a significant feature of malignancy in human cells. [source] | ||||||||||