Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:Q07644 (polypeptide)
 72,197 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Chaperonins are ubiquitous multisubunit toroidal complexes that aid protein folding in an ATP-dependent manner. Current models of folding by the bacterial chaperonin GroEL depict its role as unfolding and releasing molecules that have misfolded, so that they can return to a potentially productive folding pathway in solution. Accordingly, a given target polypeptide might require several cycles of binding and ATP-driven release from different chaperonin complexes before reaching the native state. Surprisingly, cycling of a target protein does not guarantee its folding, and we report here that unfolded beta-actin or alpha-tubulin both form tight complexes when presented to either GroEL or its mitochondrial homologue, and both undergo cycles of release and rebinding upon incubation with ATP, but no native protein is produced. We conclude that different chaperonins produce distinctive spectra of folding intermediates.
 ...
PMID:Specificity in chaperonin-mediated protein folding. 774 29

A Caenorhabditis elegans (Ce) homologue to the eukaryotic tcp-1 gene (encoding t-complex polypeptide-1) has been mapped, isolated and sequenced. Ce tcp-1 is a single-copy gene located on chromosome II. Nucleotide sequence analysis of the gene reveals the presence of four introns in the coding region and repetitive elements upstream from the start codon. The predicted Ce TCP-1 protein displays more than 60% amino-acid sequence identity to other eukaryotic TCP-1, suggesting a common origin and function for these proteins. The primary tcp-1 transcript undergoes trans-splicing to the spliced leader SL1 RNA, in addition to cis-splicing, to yield a single mRNA species of 1.9 kb. Northern blot analysis shows that unlike the evolutionarily related Hsp60 chaperonin genes, tcp-1 is not upregulated at elevated temperatures, but instead appears to be down-regulated. Additionally, the overall level of the tcp-1 transcript is approximately constant throughout the development of the nematode. The Ce chaperonin-containing TCP-1 (CCT) was identified. A protein extract made from Ce embryos was subjected to sucrose gradient fractionation and ATP-agarose chromatography. Western blot analysis of the purified protein fractions, using anti-mouse TCP-1 monoclonal antibody and antibodies raised against Ce TCP-1, reveals that Ce TCP-1 is a 57-kDa protein subunit of a high-molecular-mass complex capable of binding ATP.
 ...
PMID:Molecular analysis of Caenorhabditis elegans tcp-1, a gene encoding a chaperonin protein. 775 63

The use of noncovalent hydrophobic probes such as bis-ANS has become increasingly popular in gaining structural information about protein structure and conformation. While these probes have provided rich information about protein conformation, specific information has been limited. In this report, we extend the usefulness of the probe bis-ANS by showing that it can be covalently photoincorporated into various proteins. Using the chaperonin GroEL, we have shown that it is possible to locate important hydrophobic surfaces through photoincorporation and peptide sequencing. It has been proposed that hydrophobic surfaces on the chaperonin may be responsible for the binding of unfolded polypeptides. We show here that photoincorporation of bis-ANS is able to locate a distinct hydrophobic surface on GroEL. Incorporation of the bis-ANS occurs within a 45 residue fragment of the monomer near the middle of the primary sequence. Interestingly, photoincorporation occurs within this fragment in both tetradecamers and assembly-competent monomers. From the three-dimensional structure of GroEL, this region maps to the apical domain (residues 191-376), which has been implicated in polypeptide binding [Fenton, W. A., Kashi, Y., Furtak, K., & Horwich, A. L. (1994) Nature 371, 614-619]. In addition, the fluorescent properties of the probe are retained including the excitation and emission maxima and the sensitivity to the polarity of its environment. These results suggest that photoincorporated bis-ANS may be a useful probe for protein structure and dynamics.
 ...
PMID:Photoincorporation of 4,4'-bis(1-anilino-8-naphthalenesulfonic acid) into the apical domain of GroEL: specific information from a nonspecific probe. 777 87

We have isolated a chaperonin from the hyperthermophilic archaeon Sulfolobus solfataricus based on its ability to inhibit the spontaneous refolding at 50 degrees C of dimeric S. solfataricus malic enzyme. The chaperonin, a 920-kDa oligomer of 57-kDa subunits, displays a potassium-dependent ATPase activity with an optimum temperature at 80 degrees C. S. solfataricus chaperonin promotes correct refoldings of several guanidine hydrochloride-denatured enzymes from thermophilic and mesophilic sources. At a molar ratio of chaperonin oligomer to single polypeptide chain of 1:1, S. solfataricus chaperonin completely inhibits spontaneous refoldings and suppresses aggregation upon dilution of the denaturant; refoldings resume upon ATP hydrolysis, with yields of active molecules and rates of folding notably higher than in spontaneous processes. S. solfataricus chaperonin prevents the irreversible inactivations at 90 degrees C of several thermophilic enzymes by the binding of the denaturation intermediate; the time-courses of inactivations are unaffected and most activity is regained upon hydrolysis of ATP. S. solfataricus chaperonin completely prevents the formation of aggregates during thermal inactivation of chicken egg white lysozyme at 70 degrees C, without affecting the rate of activity loss; ATP hydrolysis results in the recovery of most lytic activity. Tryptophan fluorescence measurements provide evidence that S. solfataricus chaperonin undergoes a dramatic conformational rearrangement in the presence of ATP/Mg, and that the hydrolysis of ATP is not required for the conformational change. The ATP/Mg-induced conformation of the chaperonin is fully unable to bind the protein substrates, probably due to disappearance or modification of the substrate binding sites. This is the first archaeal chaperonin whose involvement in protein folding has been demonstrated.
 ...
PMID:The chaperonin from the archaeon Sulfolobus solfataricus promotes correct refolding and prevents thermal denaturation in vitro. 783 6

The molecular chaperone GroEl from Escherichia coli is a member of the highly conserved Hsp60 family of proteins that facilitates protein folding. A central question regarding the mechanism of GroEL-assisted refolding of proteins concerns its broad substrate specificity. The nature of GroEL-polypeptide chain interaction was investigated by isothermal titration calorimetry using proteins that maintain a non-native conformation in neutral buffer solutions. A single molecule of an unfolded variant of subtilisin BPN' binds non-cooperatively to GroEL with micromolar affinity and a positive enthalpy change. Additional calorimetric titrations of this chain with GroEL show that the positive enthalpy change decreases with increasing temperature between 6 and 25 degrees C, yielding a delta CP of -0.85 kcal mol-1 degree-1. alpha-Casein similarly binds to GroEL with micromolar affinity and a positive enthalpy change in the range of 15-20 degrees C, yielding a delta CP of -0.44 kcal mol-1 degree-1. The negative heat capacity change provides strong evidence for the role of hydrophobic interactions as the driving force for the association of these substrates with the GroEL chaperonin.
 ...
PMID:The hydrophobic nature of GroEL-substrate binding. 783 52

CCT (also called the TCP-1 complex or TriC) is a chaperonin found in the eukaryotic cytosol, and has unique structural and functional features. Unlike homo-oligomeric chaperonins, CCT comprises at least eight different subunits, and appears to have a limited range of physiological substrates. We have analysed CCT sequences in light of the recent determination of the crystal structure and mutational identification of the functional domains of the bacterial chaperonin GroEL. A high level of identity among all chaperonin subunits is observed in those regions that correspond to the ATP-binding site of GroEL. By contrast, no significant identity is shared in the region corresponding to the polypeptide-binding region of GroEL, either between CCT subunits or between CCT subunits and GroEL. This suggests that the polypeptide-binding sites of CCT subunits have diverged both from each other and from GroEL, which may explain the apparently different range of substrates recognized by CCT.
 ...
PMID:Cystosolic chaperonin subunits have a conserved ATPase domain but diverged polypeptide-binding domains. 784 67

The chaperonin containing t-complex polypeptide 1 (TCP-1), as one of its subunits, CCT, is a cytosolic heterooligomeric molecular chaperone assisting in the folding of proteins in eukaryotic cytosol. We have isolated a Tcp-1-related 119-bp cDNA fragment from a human cDNA library by polymerase chain reaction, and cloned full-length mouse cDNAs orthologous to the human cDNA by hybridization. The nucleotide (nt) sequence of the longest mouse clone (1844 bp) shows an open reading frame (ORF) encoding a TCP-1-related polypeptide of 548 amino acids (aa) (59,562 Da). This gene is different from Tcp-1 and the six Tcp-1-related genes reported previously, Tcp-1 (Ccta), Cctb, Cctg, Cctd, Ccte, Cctz and Ccth, which encode subunits of CCT. The product of the novel gene was analysed using an antibody raised against the C terminus of the polypeptide deduced from the nt sequence. We found that this gene encodes a subunit of CCT (polypeptide S1; 62 kDa and pI 6.25 by two-dimensional gel analysis). We have named it Cctq, encoding the theta subunit of CCT (CCT theta). The aa sequence of CCT theta shows 23-29% identity to the other CCT subunits, alpha, beta, gamma, delta, epsilon, zeta and eta, and 29% identity to the archaebacterial chaperonin TF55. CCT theta also contains the motifs common to all the other subunits of CCT which are postulated to be involved in ATPase activity.
 ...
PMID:The eighth Cct gene, Cctq, encoding the theta subunit of the cytosolic chaperonin containing TCP-1. 789 Jan 69

The reaction mechanism of protein folding by the chaperonin GroEL and its regulator GroES has been defined. GroES and substrate protein counteract each other's effects on GroEL: whereas GroES stabilizes GroEL in the ADP-bound state, binding of unfolded polypeptide within the cavity of the GroEL cylinder triggers ADP and GroES release. Upon ADP-ATP exchange, GroES reassociates with GroEL and ATP hydrolysis discharges the bound protein for folding. Partially folded protein rebinds to the chaperonin, thus perpetuating the cycle until folding is complete.
 ...
PMID:The reaction cycle of GroEL and GroES in chaperonin-assisted protein folding. 790 69

We have established a system for assembly of hepatitis B virus capsid, a homomultimer of the viral core polypeptide, using cell-free transcription-linked translation. The mature particles that are produced are indistinguishable from authentic viral capsids by four criteria: velocity sedimentation, buoyant density, protease resistance, and electron microscopic appearance. Production of unassembled core polypeptides can be uncoupled from production of capsid particles by decreasing core mRNA concentration. Addition of excess unlabeled core polypeptides allows the chase of the unassembled polypeptides into mature capsids. Using this cell-free system, we demonstrate that assembly of capsids proceeds by way of a novel high molecular weight intermediate. Upon isolation, the high molecular weight intermediate is productive of mature capsids when energy substrates are manipulated. A 60-kD protein related to the chaperonin t-complex polypeptide 1 (TCP-1) is found in association with core polypeptides in two different assembly intermediates, but is not associated with either the initial unassembled polypeptides or with the final mature capsid product. These findings implicate TCP-1 or a related chaperonin in viral assembly and raise the possibility that eukaryotic cytosolic chaperonins may play a distinctive role in multimer assembly apart from their involvement in assisting monomer folding.
 ...
PMID:A eukaryotic cytosolic chaperonin is associated with a high molecular weight intermediate in the assembly of hepatitis B virus capsid, a multimeric particle. 790 22

In the cytoplasm of eukaryotes, the folding of actins and tubulins is facilitated via interaction with a heteromeric toroidal complex (cytoplasmic chaperonin). The folding reaction consists of the formation of a binary complex between the unfolded target protein and the chaperonin, followed by the ultimate release of the native polypeptide in an ATP-dependent reaction. Here we show that the mitochondrial chaperonin (cpn60) and the cytoplasmic chaperonin both recognize a range of target proteins with different relative affinities; however, the cytoplasmic chaperonin shows the highest affinity for intermediates derived from unfolded tubulins and actins. These high-affinity actin and tubulin folding intermediates are distinct from the "molten globule" intermediates formed by noncytoskeletal target proteins in that they form relatively slowly. We show that the interaction between cytoplasmic chaperonin and unfolded target proteins depends on the chaperonin being in its ADP-bound state and that the release of the target protein occurs after a transition of the chaperonin to the ATP-bound state. Our data suggest a model in which ATP hydrolysis acts as a switch between conformational forms of the cytoplasmic chaperonin that interact either strongly or weakly with unfolded substrates.
 ...
PMID:Facilitated folding of actins and tubulins occurs via a nucleotide-dependent interaction between cytoplasmic chaperonin and distinctive folding intermediates. 790 54


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>