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Chaperone-like Activity (chaperone-like + activity)

Distribution by Scientific Domains

Chemistry	53%
Life Sciences	46%

Selected Abstracts

Chaperone-like activities of different molecular forms of ,-casein.

BIOPOLYMERS, Issue 8 2009
Importance of polarity of N-terminal hydrophilic domain
Abstract As a member of intrinsically unstructured protein family, ,-casein (,-CN) contains relatively high amount of prolyl residues, adopts noncompact and flexible structure and exhibits chaperone-like activity in vitro. Like many chaperones, native ,-CN does not contain cysteinyl residues and exhibits strong tendencies for self-association. The chaperone-like activities of three recombinant ,-CNs wild type (WT) ,-CN, C4 ,-CN (with cysteinyl residue in position 4) and C208 ,-CN (with cysteinyl residue in position 208), expressed and purified from E. coli, which, consequently, lack the phosphorylated residues, were examined and compared with that of native ,-CN using insulin and alcohol dehydrogenase as target/substrate proteins. The dimers (,-CND) of C4-,-CN and C208 ,-CN were also studied and their chaperone-like activities were compared with those of their monomeric forms. Lacking phosphorylation, WT ,-CN, C208 ,-CN, C4 ,-CN and C4 ,-CND exhibited significantly lower chaperone-like activities than native ,-CN. Dimerization of C208 ,-CN with two distal hydrophilic domains considerably improved its chaperone-like activity in comparison with its monomeric form. The obtained results demonstrate the significant role played by the polar contributions of phosphorylated residues and N-terminal hydrophilic domain as important functional elements in enhancing the chaperone-like activity of native ,-CN. © 2009 Wiley Periodicals, Inc. Biopolymers 91: 623,632, 2009. This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source]

Chaperone-like activity and hydrophobicity of ,-crystallin

IUBMB LIFE, Issue 11 2006
G. Bhanuprakash Reddy
Abstract ,-Crystallin, a prominent member of small heat shock protein (sHsp) family and a major structural protein of the eye lens is a large polydisperse oligomer of two isoforms, ,A- and ,B-crystallins. Numerous studies have demonstrated that ,-crystallin functions like a molecular chaperone in preventing the aggregation of various proteins under a wide range of stress conditions. The molecular chaperone function of ,-crystallin is thus considered to be vital in the maintenance of lens transparency and in cataract prevention. ,-Crystallin selectively interacts with non-native proteins thereby preventing them from aggregation and helps maintain them in a folding competent state. It has been proposed and generally accepted that ,-crystallin suppresses the aggregation of other proteins through the interaction between hydrophobic patches on its surface and exposed hydrophobic sites of partially unfolded substrate protein. However, a quantifiable relationship between hydrophobicity and chaperone-like activity remains a matter to be concerned about. On an attentive review of studies on ,-crystallin chaperone-like activity, particularly the studies that have direct or indirect implications to hydrophobicity and chaperone-like activity, we found several instances wherein the correlation between hydrophobicity and its chaperone-like activity is paradoxical. We thus attempted to provide an overview on the role of hydrophobicity in chaperone-like activity of ,-crystallin, the kind of evaluation done for the first time. iubmb Life, 58: 632 - 641, 2006 [source]

Mechanochemical ATPases and transcriptional activation

MOLECULAR MICROBIOLOGY, Issue 4 2002
X. Zhang
Summary Transcriptional activator proteins that act upon the ,54 -containing form of the bacterial RNA polymerase belong to the extensive AAA+ superfamily of ATPases, members of which are found in all three kingdoms of life and function in diverse cellular processes, often via chaperone-like activities. Formation and collapse of the transition state of ATP for hydrolysis appears to engender the interaction of the activator proteins with ,54 and leads to the protein structural transitions needed for RNA polymerase to isomerize and engage with the DNA template strand. The common oligomeric structures of AAA+ proteins and the crea-tion of the active site for ATP hydrolysis between protomers suggest that the critical changes in protomer structure required for productive interactions with ,54 -holoenzyme occur as a consequence of sensing the state of the , -phosphate of ATP. Depending upon the form of nucleotide bound, different functional states of the activator are created that have distinct substrate and chaperone-like binding activ-ities. In particular, interprotomer ATP interactions rely upon the use of an arginine finger, a situation reminiscent of GTPase-activating proteins. [source]

Chaperone-like activities of different molecular forms of ,-casein.

Effect of mutations in the ,5,,7 loop on the structure and properties of human small heat shock protein HSP22 (HspB8, H11)

FEBS JOURNAL, Issue 21 2007
Alexei S. Kasakov
The human genome encodes ten different small heat shock proteins, each of which contains the so-called ,-crystallin domain consisting of 80,100 residues and located in the C-terminal part of the molecule. The ,-crystallin domain consists of six or seven ,-strands connected by different size loops and combined in two ,-sheets. Mutations in the loop connecting the ,5 and ,7 strands and conservative residues of ,7 in ,A-, ,B-crystallin and HSP27 correlate with the development of different congenital diseases. To understand the role of this part of molecule in the structure and function of small heat shock proteins, we mutated two highly conservative residues (K137 and K141) of human HSP22 and investigated the properties of the K137E and K137,141E mutants. These mutations lead to a decrease in intrinsic Trp fluorescence and the double mutation decreased fluorescence resonance energy transfer from Trp to bis-ANS bound to HSP22. Mutations K137E and especially K137,141E lead to an increase in unordered structure in HSP22 and increased susceptibility to trypsinolysis. Both mutations decreased the probability of dissociation of small oligomers of HSP22, and mutation K137E increased the probability of HSP22 crosslinking. The wild-type HSP22 possessed higher chaperone-like activity than their mutants when insulin or rhodanase were used as the model substrates. Because conservative Lys residues located in the ,5,,7 loop and in the ,7 strand appear to play an important role in the structure and properties of HSP22, mutations in this part of the small heat shock protein molecule might have a deleterious effect and often correlate with the development of different congenital diseases. [source]

Chaperone-like activity and hydrophobicity of ,-crystallin

TorsinA and heat shock proteins act as molecular chaperones: suppression of ,-synuclein aggregation

JOURNAL OF NEUROCHEMISTRY, Issue 4 2002
Pamela J. McLean
Abstract TorsinA, a protein with homology to yeast heat shock protein104, has previously been demonstrated to colocalize with ,-synuclein in Lewy bodies, the pathological hallmark of Parkinson's disease. Heat shock proteins are a family of chaperones that are both constitutively expressed and induced by stressors, and that serve essential functions for protein refolding and/or degradation. Here, we demonstrate that, like torsinA, specific molecular chaperone heat shock proteins colocalize with ,-synuclein in Lewy bodies. In addition, using a cellular model of ,-synuclein aggregation, we demonstrate that torsinA and specific heat shock protein molecular chaperones colocalize with ,-synuclein immunopositive inclusions. Further, overexpression of torsinA and specific heat shock proteins suppress ,-synuclein aggregation in this cellular model, whereas mutant torsinA has no effect. These data suggest that torsinA has chaperone-like activity and that the disease-associated GAG deletion mutant has a loss-of-function phenotype. Moreover, these data support a role for chaperone proteins, including torsinA and heat shock proteins, in cellular responses to neurodegenerative inclusions. [source]

Stepwise disassembly and apparent nonstepwise reassembly for the oligomeric RbsD protein

PROTEIN SCIENCE, Issue 6 2006
Yongjun Feng
Abstract Many cellular proteins exist as homo-oligomers. The mechanism of the assembly process of such proteins is still poorly understood. We have previously observed that Hsp16.3, a protein exhibiting chaperone-like activity, undergoes stepwise disassembly and nonstepwise reassembly. Here, the disassembly and reassembly of a nonchaperone protein RbsD, from Escherichia coli, was studied in vitro. The protein was found to mainly exist as decamers with a small portion of apparently larger oligomeric forms, both of which are able to refold/reassemble effectively in a spontaneous way after being completely unfolded. Disassembly RbsD intermediates including pentamers, tetramers, trimers, dimers, and monomers were detected by using urea-containing pore gradient polyacrylamide gel electrophoresis, while only pentamers were detected for its reassembly. The observation of stepwise disassembly and apparent nonstepwise reassembly for both a chaperone protein (Hsp16.3) and a nonchaperone protein (RbsD) strongly suggests that such a feature is most likely general for homo-oligomeric proteins. [source]

Chaperone-like activities of different molecular forms of ,-casein.

Effect of Doxycycline-Regulated ERp57 Expression on Specific Thrombopoietin Productivity of Recombinant CHO Cells

BIOTECHNOLOGY PROGRESS, Issue 1 2003
Sun Ok Hwang
In an attempt to increase the specific thrombopoietin (TPO) productivity ( qTPO) of recombinant Chinese hamster ovary (rCHO) cells (TPO-33), the effect of expression level of ERp57, an isoform of protein disulfide isomerase, on qTPO was investigated. To regulate ERp57 expression level, the Tet-Off system was first introduced in TPO-33 cells and stable Tet-Off cells (TPO-33-Tet-Off) were screened by the luciferase assay. The rCHO cells with a doxycycline-regulated ERp57 expression system (TPO-33-ERp57) were obtained by cotransfection of pTRE-ERp57 and pTK-Hyg expression vectors into TPO-33-Tet-Off cells and subsequent screening by Western blot analysis of ERp57 and an enzyme-linked immunosorbent assay of secreted TPO. Western blot analysis showed that ERp57 expression level in TPO-33-ERp57 cells could be regulated tightly by the addition of different concentrations of doxycycline to a culture medium. A doxycycline concentration of 1 ,g/mL, which did not influence cell growth and TPO production of TPO-33-Tet-Off cells, was high enough to suppress the ERp57 expression to a basal level. Compared with the basal level, a 1.7-fold increase in ERp57 expression level was obtained in the absence of doxycycline. This increased expression level of ERp57 resulted in a 2.1-fold increase in qTPO without growth inhibition, probably as a result of the chaperone-like activity of ERp57 in CHO cells. Taken together, the results obtained here demonstrate that qTPO of rCHO cells can be increased by elevating the expression level of ERp57. [source]