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Order Martellivirales: Virgaviridae
Published in Paul Pumpens, Peter Pushko, Philippe Le Mercier, Virus-Like Particles, 2022
Paul Pumpens, Peter Pushko, Philippe Le Mercier
Developing further the E. coli expression of the TMV coat gene, Hwang et al. (1998) found that both GroEL and DnaK chaperons had significant direct or indirect effects on the overall expression, stability, folding, and assembly of the TMV coat protein in vivo. The overproduction of GroEL or GroES alone had little effect. However, cooverexpression of GroEL and GroES resulted in a twofold increase in soluble TMV coat and a fourfold rise in the assembled TMV-like particles in vivo. Moreover, TMV coat was shown to interact directly with GroEL in vivo (Hwang et al. 1998). Later, Dedeo et al. (2010) constructed and expressed in E. coli a “circular permutant” of TMV coat, where the N- and C-termini were reengineered, and a short loop was placed to close the sequence gap, as described later in detail.
The Stress Response and Stress Proteins
Published in John J. Lemasters, Constance Oliver, Cell Biology of Trauma, 2020
Martin E. Feder, Dawn A. Parsell, Susan L. Lindquist
In the cell, these two groups of chaperones apparently work together to promote protein folding in the bacterial cell. DnaK is hypothesized to bind to extensively unfolded proteins; DnaJ then prevents release of these proteins as some folding ensues. GrpE is then thought to promote the transfer of the partially folded protein from DnaJ-DnaK to GroEL, which in combination with GroES, completes the folding reaction. In GroEL, 14 subunits of approximately 60 kD form two stacked seven-member rings surrounding a common central cavity. GroES, also in a seven-member ring, can bind to either end of the GroEL cylinder to form a complex. Martin et al.27 recently proposed a model of how the GroEL-GroES-unfolded protein complex mediates protein folding (Figure 5). According to their model, unfolded protein binds to the inside of the “cage” formed by the two GroEL rings. Binding of GroES to the complex reduces the affinity of GroEL for the unfolded protein, causing their dissociation. The unfolded protein is then free to fold, and the GroEL cage surrounding it shields it from inappropriate interactions with other proteins. If folding is complete, GroEL no longer has affinity for the mature protein, which will exit from the cage. If folding is incomplete, the protein can again be bound by the interior of the GroEL cage, which prompts the dissociation of GroES from the complex. The free GroES is then available to initiate a subsequent cycle of release, folding, and either exit or rebinding of the unfolded protein. Although many details of this model remain to be verified, it provides an intriguing glimpse of how chaperones may work28.
Hydrogen deuterium exchange mass spectrometry applied to chaperones and chaperone-assisted protein folding
Published in Expert Review of Proteomics, 2019
Florian Georgescauld, Thomas E. Wales, John R. Engen
Chaperonins constitute an essential class of chaperones formed by two identical rings of about 0.5 MDa each, stacked back to back. Two groups of chaperonins exist: group I chaperonins present in bacteria (GroEL/GroES), mitochondria (Hsp60/Hsp10) and chloroplasts (Cpn60/Cpn10), and group II chaperonins present in eukaryotes (TriC also called CCT) and archaea (thermosome). GroEL/GroES, the most studied chaperonin, is the only essential molecular chaperone in E. coli and interacts with 250 different cytosolic proteins [16]. About 80 of the 250 proteins are ‘strictly dependent’ substrates (or class III substrates) because at 37°C they are unable to acquire their native structure without help from GroEL/GroES and aggregate rapidly. Natural substrates of GroEL/GroES are frequently proteins that include a TIM-barrel domain, with half of the chaperone substrates being of this variety. GroEL consists of a double ring of seven identical subunits forming a central cavity that can hold proteins between 20 and 60 kDa in size. In the presence of ATP and GroES, one substrate protein at a time will be encapsulated for about 10 s in the ‘nano-compartment’ formed by GroEL/GroES, so that folding can occur. Determining how GroEL/GroES actively promotes folding of the encapsulated substrate protein is a key question in the protein folding field. The eukaryotic cognate of GroEL is the chaperonin TRiC, composed of two rings of eight different paralogous subunits (reviewed in [17]). No analogous GroES lid covers the rings in TRiC, but a built-in lid is formed from apical protrusions of each subunit. Substrates of prokaryotic and eukaryotic chaperonins are different, suggesting different functional mechanisms.
Chaperonomics in leptospirosis
Published in Expert Review of Proteomics, 2018
Arada Vinaiphat, Visith Thongboonkerd
GroES and GroEL are products of the groE operon found in a large number of bacterial organisms. The GroE complex comprises a total of 14 GroEL subunits arranged in a dual-ring tetradecamer to form a cylindrical-shape complex, with apical domain as a binding site for its cochaperone GroES in the presence of ATP [3,4]. Binding of GroES induces the substrate protein to move from the rim into the interior part of the cylindrical cavity. The hydrophilic environment within the cavity favors burying of hydrophobic residuals of the substrate, causing the substrate to fold. Hydrolysis of ATP then causes a release of the substrate back into the cytosol, allowing a new substrate to bind for starting a new cycle [5]. In eukaryotes, GroES and GroEL homologs are structurally and functionally similar to Hsp10 and Hsp60, respectively [2]. The importance of GroES and GroEL is reflected by their high levels within the cells that are approximately 2% of all cellular proteins during normal condition and even greater at high temperature or under stresses [6]. GroE machinery has been demonstrated to play role in folding and assembly of proteins, RNA and DNA [7], and bacterial growth [8]. GroEL complex contributes to stress resistance by assisting folding of a large variety of unfolded or partially folded proteins to prevent protein denaturation and to reform partially denatured proteins [4]. Moreover, GroEL can interact to over a half of non-native proteins in Escherichia coli [9]. Based on previous findings and recent evidence, this low specificity between substrates and GroE complex can be explained by the favorable interaction between hydrophobic cavity of GroEL and the exposed hydrophobic residues of non-native proteins that are normally buried inside the native forms [10]. Such property in assisting protein folding suggests its indispensable role for stress resistance in bacterial cells.