Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:Q86TM3 (cage)
 29,987 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The chaperonin system, GroEL and GroES of Escherichia coli enable certain proteins to fold under conditions when spontaneous folding is prohibitively slow as to compete with other non-productive channels such as aggregation. We investigated the plausible mechanisms of GroEL-mediated folding using simple lattice models. In particular, we have investigated protein folding in a confined environment, such as those offered by the GroEL, to decipher whether rate and yield enhancement can occur when the substrate protein is allowed to fold within the cavity of the chaperonins. The GroEL cavity is modeled as a cubic box and a simple bead model is used to represent the substrate chain. We consider three distinct characteristic of the confining environment. First, the cavity is taken to be a passive Anfinsen cage in which the walls merely reduce the available conformation space. We find that at temperatures when the native conformation is stable, the folding rate is retarded in the Anfinsen cage. We then assumed that the interior of the wall is hydrophobic. In this case the folding times exhibit a complex behavior. When the strength of the interaction between the polypeptide chain and the cavity is too strong or too weak we find that the rates of folding are retarded compared to spontaneous folding. There is an optimum range of the interaction strength that enhances the rates. Thus, above this value there is an inverse correlation between the folding rates and the strength of the substrate-cavity interactions. The optimal hydrophobic walls essentially pull the kinetically trapped states which leads to a smoother the energy landscape. It is known that upon addition of ATP and GroES the interior cavity of GroEL offers a hydrophilic-like environment to the substrate protein. In order to mimic this within the context of the dynamic Anfinsen cage model, we allow for changes in the hydrophobicity of the walls of the cavity. The duration for which the walls remain hydrophobic during one cycle of ATP hydrolysis is allowed to vary. These calculations show that frequent cycling of the wall hydrophobicity can dramatically reduce the folding times and increase the yield as well under non-permissive conditions. Examination of the structures of the substrate proteins before and after the change in hydrophobicity indicates that there is global unfolding involved. In addition, it is found that a fraction of the molecules kinetically partition to the native state in accordabce with the iterative annealing mechanism. Thus, frequent "unfoldase" activity of chaperonins leading to global unfolding of the polypeptide chain results in enhancement of the folding rates and yield of the folded protein. We suggest that chaperonin efficiency can be greatly enhanced if the cycling time is reduced. The calculations are used to interpret a few experiments on chaperonin-mediated protein folding.
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PMID:Exploring the kinetic requirements for enhancement of protein folding rates in the GroEL cavity. 1009 64

Trypanosomatids have a striking cage-like arrangement of submembraneous microtubules. We previously showed that alpha- and beta- tubulins of these stable microtubules are extensively modified by polyglutamylation. Cytoskeletal microtubular preparations obtained by Triton extraction of Leishmania tarentolae and Crithidia fasciculata retain an enzymatic activity that incorporates radioactive glutamic acid in a Mg2+-ATP-dependent manner into alpha- and beta-tubulins. The tubulin polyglutamylase is extracted by 0.25 M salt. The Crithidia enzyme can be purified by ATP-affinity chromatography, glycerol-gradient centrifugation and ion-exchange chromatography. After extraction from the microtubular cytoskeleton the glutamylase forms a complex with alphabeta tubulin, but behaves after removal of tubulin as a globular protein with a molecular mass of 38x10(3). In highly enriched fractions a corresponding band is the major polypeptide visible in SDS-PAGE. The enzyme from Crithidia recognises mammalian brain tubulin, where it incorporates glutamic acid preferentially into the more acidic variants of both alpha- and beta-tubulins. Synthetic peptides with an oligoglutamyl side chain, corresponding to the carboxy-terminal end of brain alpha- and beta-tubulins, are accepted by the enzyme, albeit at low efficiency. The polyglutamylase elongates the side chain by up to 3 and 5 residues, respectively. Other properties of the tubulin polyglutamylase are also discussed.
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PMID:Isolation of tubulin polyglutamylase from Crithidia; binding to microtubules and tubulin, and glutamylation of mammalian brain alpha- and beta-tubulins. 1036 48

The cylindrical chaperonin GroEL of E. coli and its ring-shaped cofactor GroES cooperate in mediating the ATP-dependent folding of a wide range of polypeptides in vivo and in vitro. By binding to the ends of the GroEL cylinder, GroES displaces GroEL-bound polypeptide into an enclosed folding cage, thereby preventing protein aggregation during folding. The dynamic interaction of GroEL and GroES is regulated by the GroEL ATPase and involves the formation of asymmetrical GroEL:GroES1 and symmetrical GroEL: GroES2 complexes. The proposed role of the symmetrical complex as a catalytic intermediate of the chaperonin mechanism has been controversial. It has also been suggested that the formation of GroEL:GroES2 complexes allows the folding of two polypeptide molecules per GroEL reaction cycle, one in each ring of GroEL. By making use of a procedure to stabilize chaperonin complexes by rapid crosslinking for subsequent analysis by native PAGE, we have quantified the occurrence of GroEL:GroES1 and GroEL:GroES2 complexes in active refolding reactions under a variety of conditions using mitochondrial malate dehydrogenase (mMDH) as a substrate. Our results show that the symmetrical complexes are neither required for chaperonin function nor does their presence significantly increase the rate of mMDH refolding. In contrast, chaperonin-assisted folding is strictly dependent on the formation of asymmetrical GroEL:GroES1 complexes. These findings support the view that GroEL:GroES2 complexes have no essential role in the chaperonin mechanism.
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PMID:On the role of symmetrical and asymmetrical chaperonin complexes in assisted protein folding. 1038 59

Human erythrocyte sugar transport presents a functional complexity that is not explained by existing models for carrier-mediated transport. It has been suggested that net sugar uptake is the sum of three serial processes: sugar translocation, sugar interaction with an intracellular binding complex, and the release from this complex into bulk cytosol. The present study was carried out to identify the erythrocyte sugar binding complex, to determine whether sugar binding occurs inside or outside the cell, and to determine whether this binding complex is affected by cytosolic ATP or transporter quaternary structure. Sugar binding assays using cells and membrane protein fractions indicate that sugar binding to erythrocytes is quantitatively accounted for by sugar binding to the hexose transport protein, GluT1. Kinetic analysis of net sugar fluxes indicates that GluT1 sugar binding sites are cytoplasmic. Intracellular ATP increases GluT1 sugar binding capacity from 1 to 2 mol of 3-O-methylglucose/mol GluT1 and inhibits the release of bound sugar into cytosol. Reductant-mediated, tetrameric GluT1 dissociation into dimeric GluT1 is associated with the loss of ATP and 3-O-methylglucose binding. We propose that sugar uptake involves GluT1-mediated, extracellular sugar translocation into an ATP-dependent cage formed by GluT1 cytoplasmic domains. Caged or occluded sugar has three possible fates: (1) transport out of the cell (substrate cycling); (2) interaction with sugar binding sites within the cage, or (3) release into bulk cytosol. We show how this hypothesis can account for the complexity of erythrocyte sugar transport and its regulation by cytoplasmic ATP.
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PMID:ATP-dependent substrate occlusion by the human erythrocyte sugar transporter. 1071 21

The chaperonin HSP60 (GroEL) proteins are essential in eubacterial genomes and in eukaryotic organelles. Functional regions inferred from mutation studies and the Escherichia coli GroEL 3D crystal complexes are evaluated in a multiple alignment across 43 diverse HSP60 sequences, centering on ATP/ADP and Mg2+ binding sites, on residues interacting with substrate, on GroES contact positions, on interface regions between monomers and domains, and on residues important in allosteric conformational changes. The most evolutionary conserved residues relate to the ATP/ADP and Mg2+ binding sites. Hydrophobic residues that contribute in substrate binding are also significantly conserved. A large number of charged residues line the central cavity of the GroEL-GroES complex in the substrate-releasing conformation. These span statistically significant intra- and inter-monomer three-dimensional (3D) charge clusters that are highly conserved among sequences and presumably play an important role interacting with the substrate. Unaligned short segments between blocks of alignment are generally exposed at the outside wall of the Anfinsen cage complex. The multiple alignment reveals regions of divergence common to specific evolutionary groups. For example, rickettsial sequences diverge in the ATP/ADP binding domain and gram-positive sequences diverge in the allosteric transition domain. The evolutionary information of the multiple alignment proffers attractive sites for mutational studies.
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PMID:Conservation among HSP60 sequences in relation to structure, function, and evolution. 1075 9

Cancer is frequently associated with anorexia, weight loss, negative nitrogen balance, and skeletal-muscle wasting. Depletion of skeletal-muscle mass is critical to overall survival of the patient, can prolong rehabilitation to normal function after recovery, and decreases quality of life in a palliative-care setting. The biochemical and physiologic bases of cancer-associated muscle wasting have been most fully investigated in animal models. These studies provide evidence for suppressed protein synthesis and activated proteolysis in cancer-associated muscle wasting and indicate a need for both anabolic and anticatabolic therapies. Several humoral factors of host or tumor origin are implicated in altered muscle-protein metabolism, including cytokines, metabolites of arachidonic acid, and a proteolysis-inducing glycoprotein; their interrelationships are less well characterized. Several catabolic mediators may share common downstream mechanisms because they ultimately activate the ATP-, ubiquitin-, and proteasome-dependent intracellular proteolytic system. Although important gaps in our current understanding remain, data available from animal studies can be used as a basis to develop relevant studies in human subjects.
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PMID:Regulation of skeletal-muscle-protein turnover in cancer-associated cachexia. 1105 10

The GroEL/GroES chaperonin system mediates the folding of a range of newly synthesized polypeptides in the bacterial cytosol. Using a rapid biotin-streptavidin-based inhibition of chaperonin function, we show that the cage formed by GroEL and its cofactor GroES can have a dual role in promoting folding. First, enclosure of nonnative protein in the GroEL:GroES complex is essential for folding to proceed unimpaired by aggregation. Second, folding inside the cage can be significantly faster than folding in free solution, independently of ATP-driven cycles of GroES binding and release. This suggests that confinement of unfolded protein in the narrow hydrophilic space of the chaperonin cage smoothes the energy landscape for the folding of some proteins, increasing the flux of folding intermediates toward the native state.
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PMID:Dual function of protein confinement in chaperonin-assisted protein folding. 1167 29

The bacterial chaperonin GroEL functions with its cofactor GroES in assisting the folding of a wide range of proteins in an ATP-dependent manner. GroEL-GroES constitute one of the main chaperone systems in the Escherichia coli cytoplasm. The chaperonin facilitates protein folding by enclosing substrate proteins in a cage defined by the GroEL cylinder and the GroES cap where folding can take place in a protected environment. The in vivo role of GroEL has recently been elucidated. GroEL is found to interact with 10-15% of newly synthesized proteins, with a strong preference for proteins in the molecular weight range of 20-60 kDa. A large number of GroEL substrates have been identified and were found to preferentially contain proteins with multiple alphabeta, domains that have alpha-helices and beta-sheets with extensive hydrophobic surfaces. Based on the preferential binding of GroEL to these proteins and structural and biochemical data, a model of substrate recognition by GroEL is proposed. According to this model, binding takes place preferentially between the hydrophobic residues in the apical domains of GroEL and the hydrophobic faces exposed by the beta-sheets or alpha-helices in the alphabeta domains of protein substrates.
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PMID:Mechanism of substrate recognition by the chaperonin GroEL. 1171 98

To find key genes essential for salt tolerance in the mangrove plant, Bruguiera sexangula, functional screening was performed using Escherichia coli as the host organism. A transformant expressing a cytosolic chaperonin-containing TCP-1alpha (CCTalpha) homologue displayed enhanced salt tolerance. Analysis in E. coli of the functional region revealed that a sequence of only 218 amino acids, containing the apical domain, is necessary for osmotolerance. Furthermore, this domain shows chaperone activity in vitro. Therefore, CCTalpha facilitates the folding of proteins without ATP or the cage-like structure, and may play an important role in stress tolerance, at least in B. sexangula.
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PMID:The role of plant CCTalpha in salt- and osmotic-stress tolerance. 1235 22

GroEL encapsulates nonnative substrate proteins in a central cavity capped by GroES, providing a safe folding cage. Conventional models assume that a single timer lasting approximately 8 s governs the ATP hydrolysis-driven GroEL chaperonin cycle. We examine single molecule imaging of GFP folding within the cavity, binding release dynamics of GroEL-GroES, ensemble measurements of GroEL/substrate FRET, and the initial kinetics of GroEL ATPase activity. We conclude that the cycle consists of two successive timers of approximately 3 s and approximately 5 s duration. During the first timer, GroEL is bound to ATP, substrate protein, and GroES. When the first timer ends, the substrate protein is released into the central cavity and folding begins. ATP hydrolysis and phosphate release immediately follow this transition. ADP, GroES, and substrate depart GroEL after the second timer is complete. This mechanism explains how GroES binding to a GroEL-substrate complex encapsulates the substrate rather than allowing it to escape into solution.
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PMID:GroEL mediates protein folding with a two successive timer mechanism. 1514 92


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