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1.
sHsps and their role in the chaperone network 总被引:17,自引:0,他引:17
Haslbeck M 《Cellular and molecular life sciences : CMLS》2002,59(10):1649-1657
Small Hsps (sHsps) encompass a widespread but diverse class of proteins. These low molecular mass proteins (15—42 kDa) form
dynamic oligomeric structures ranging from 9 to 50 subunits. sHsps display chaperone function in vitro, and in addition they
have been suggested to be involved in the inhibition of apoptosis, organisation of the cytoskeleton and establishing the refractive
properties of the eye lens in the case of α-crystallin. How these different functions can be explained by a common mechanism
is unclear at present. However, as most of the observed phenomena involve nonnative protein, the repeatedly reported chaperone
properties of sHsps seem to be of key importance for understanding their function. In contrast to other chaperone families,
sHsps bind several nonnative proteins per oligomeric complex, thus representing the most efficient chaperone family in terms
of the quantity of substrate binding. In some cases, the release of substrate proteins from the sHsp complex is achieved in
cooperation with Hsp70 in an ATP-dependent reaction, suggesting that the role of sHsps in the network of chaperones is to
create a reservoir of nonnative refoldable protein. 相似文献
2.
Specialised copper sites have been recruited during evolution to provide long-range electron transfer reactivity and oxygen
binding and activation in proteins destined to cope with oxygen reactivity in different organisms. Ceruloplasmin is an ancient
multicopper oxidase evolved to insure a safe handling of oxygen in some metabolic pathways of vertebrates. The presently available
knowledge of its structure provides a glimpse of its plasticity, revealing a multitude of binding sites that point to an elaborate
mechanism of multifunctional activity. Ceruloplasmin represents an example of a 'moonlighting' protein that overcomes the
one gene-one structure-one function concept to follow the changes of the organism in its physiological and pathological conditions.
Received 19 February 2002; received after revision 29 March 2002; accepted 2 April 2002
RID="*"
ID="*"Corresponding author. 相似文献
3.
Peptide aptamers have emerged as powerful new tools for molecular medicine. They can specifically bind to and functionally
inactivate a given target molecule under intracellular conditions. Typically, peptide aptamers are generated by screening
a randomized peptide expression library, displayed from the Escherichia coli thioredoxin A (TrxA) protein. Here, we transferred peptide moieties from defined TrxA-based peptide aptamers to alternative
scaffold proteins, such as the green fluorescent protein and staphylococcal nuclease. Yeast and mammalian two-hybrid assays
as well as in vitro binding analyses show that the TrxA scaffold can be a major determinant for the binding of peptide aptamers.
In addition, we demonstrate that TrxA can correctly display peptide sequences that correspond to the binding domains of natural
interaction partners. Therefore, sequence analyses of TrxA-based peptide aptamers, isolated by two-hybrid screening from randomized
expression libraries, should also be useful to find cellular binding partners for a given target protein, by homology.
Received 1 August 2002; received after revision 17 September 2002; accepted 19 September 2002
RID="*"
ID="*"Corresponding author. 相似文献
4.
Functions and malfunctions of the tau proteins 总被引:9,自引:1,他引:8
The tau proteins belong to the family of microtubule-associated proteins. They are mainly expressed in neurons where they
play major regulatory roles in the organization and integrity of the cytoskeleton network. Neurofibrillary changes of abnormally
hyperphosphorylated tau are a key lesion in Alzheimer's disease and a number of other tauopathies. However, despite an ever-increasing
body of data on the changes which tau undergoes in disease, its role regarding the fundamental disease process is still unclear.
Moreover, conceptions of tau functions continue to evolve, which complicates an understanding of its role in the disease process.
This review attempts to summarize data on the role of tau proteins in the context of both normal cellular function and dysfunction.
Furthermore, we try to develop a mechanistic framework for the involvement of tau during the disease process. The review closes
with a look towards various approaches to elucidate the functions and malfunctions of tau.
Received 21 June 2002; received after revision 24 July 2002; accepted 29 July 2002
RID="*"
ID="*"Corresponding author. 相似文献
5.
de Keyzer J van der Does C Driessen AJ 《Cellular and molecular life sciences : CMLS》2003,60(10):2034-2052
The major route of protein translocation in bacteria is the so-called general secretion pathway (Sec-pathway). This route has been extensively studied in Escherichia coli and other bacteria. The movement of preproteins across the cytoplasmic membrane is mediated by a multimeric membrane protein complex called translocase. The core of the translocase consists of a proteinaceous channel formed by an oligomeric assembly of the heterotrimeric membrane protein complex SecYEG and the peripheral adenosine triphosphatase (ATPase) SecA as molecular motor. Many secretory proteins utilize the molecular chaperone SecB for targeting and stabilization of the unfolded state prior to translocation, while most nascent inner membrane proteins are targeted to the translocase by the signal recognition particle and its membrane receptor. Translocation is driven by ATP hydrolysis and the proton motive force. In the last decade, genetic and biochemical studies have provided detailed insights into the mechanism of preprotein translocation. Recent crystallographic studies on SecA, SecB and the SecYEG complex now provide knowledge about the structural features of the translocation process. Here, we will discuss the mechanistic and structural basis of the translocation of proteins across and the integration of membrane proteins into the cytoplasmic membrane.Received 10 January 2003; received after revision 2 April 2003; accepted 4 April 2003 相似文献
6.
Watanabe H Nakashima K Saito H Slaytor M 《Cellular and molecular life sciences : CMLS》2002,59(11):1983-1992
An endo-β-1,4-glucanase (EG) was purified from the hindgut of an Australian mound-building termite, Coptotermes lacteus. The hindgut extract had a peak separate from those for extracts obtained from the salivary glands and the midgut based on
sephacryl S-200 gel chromatography, and also demonstrated an origin different from the endogenous EGs of the termite itself.
The recovery was further purified by SDS-PAGE, and its N-terminal amino acid sequence analyzed. This showed high homology
to EGs from glycoside hydrolase family (GHF) 7. PCR-based cloning methods were applied to the hindgut contents of C. lacteus and individual protozoan symbionts from C. formosanus. cDNAs encoding putative EGs homologous to GHF7 members were then identified. The functionality of one of the putative proteins
was confirmed by its expression in Escherichia coli.
Received 18 September 2002; accepted 20 September 2002
RID="*"
ID="*"Corresponding author. 相似文献
7.
Protein folding and degradation in bacteria: to degrade or not to degrade? That is the question 总被引:11,自引:0,他引:11
In Escherichia coli protein quality control is carried out by a protein network, comprising chaperones and proteases. Central to this network
are two protein families, the AAA+ and the Hsp70 family. The major Hsp70 chaperone, DnaK, efficiently prevents protein aggregation
and supports the refolding of damaged proteins. In a special case, DnaK, together with the assistance of the AAA+ protein
ClpB, can also refold aggregated proteins. Other Hsp70 systems have more specialized functions in the cell, for instance HscA
appears to be involved in the assembly of Fe/S proteins. In contrast to ClpB, many AAA+ proteins associate with a peptidase
to form proteolytic machines which remove irreversibly damaged proteins from the cellular pool. The AAA+ component of these
proteolytic machines drives protein degradation. They are required not only for recognition of the substrate but also for
substrate unfolding and translocation into the proteolytic chamber. In many cases, specific adaptor proteins modify the substrate
binding properties of AAA+ proteins. While chaperones and proteases do not appear to directly cooperate with each other, both
systems appear to be necessary for proper functioning of the cell and can, at least in part, substitute for one another.
RID="*"
ID="*"Corresponding author. 相似文献
8.
Proteins of thermophilic organisms are adapted to remain well structured and functional at elevated temperatures. Nevertheless
like their 'cousins' that reside at medium temperatures, they require the assistance of molecular chaperones to fold properly
and prevent aggregation. This review compares structural and functional properties of the DnaK/ClpB systems of Thermus thermophilus and, mainly, Escherichia coli (DnakTth and DnakEco). Many elemental properties of these systems remain conserved. However, in addition to a general increase of the thermal
stability of its components, the DnakTth system shows profound differences in its regulation, and genetic as well as oligomeric organization. Whether these differences
are unique or represent general strategies of adaptation to life at elevated temperatures remains to be clarified.
RID="*"
ID="*"Corresponding author. 相似文献
9.
Species-specific cell adhesion in marine sponges is mediated by a new family of modular proteoglycans whose general supramolecular
structure resembles that of hyalectans. However, neither their protein nor their glycan moieties have significant sequence
homology to other proteoglycans, despite having protein subunits equivalent to link proteins and to proteoglycan monomer core
proteins, and glycan subunits equivalent to hyaluronan and to the glycosaminoglycans of hyalectans. In some species, these
molecular components are assembled into a structure with a circular core formed by the link protein- and hyaluronan-like subunits.
Besides their involvement in cell adhesion, these sponge proteoglycans, for which we propose the term spongicans, participate
in signal transduction processes and are suspected to play a role in sponge self-nonself recognition. Their in vivo roles
and the mild methods used to purify large amounts of functionally active spongicans make them ideal models to study the functions
and possible new applications of proteoglycans in biomedical research.
Received 21 May 2002; received after revision 5 July 2002; accepted 10 July 2002
RID="*"
ID="*"Corresponding author. 相似文献
10.
This review traces some of the key features of the folding of β-lactamases and their relevance to the way proteins fold in general. Studies on the enzymes have highlighted the nature and
role of equilibrium and transient condensed states. The kinetics of folding are multiphasic, and when monitored by acrylamide
quenching of the tryptophan fluorescence, an early phase provides evidence for the transient accumulation of a nonnative intermediate
involving burial of tryptophan in a nonpolar environment. Intermediate phases can be understood in terms of progressive folding
of different parts of the molecule. The later, slow phases are associated with proline isomerization in the TEM-1 enzyme and,
in its P167T mutant form, with isomerization from trans to cis of the E166 T167 peptide bond. Coupled with kinetic and X-ray crystallographic studies of the β-lactamase from Staphylococcus aureus and its D179Q mutant, it appears that the final stage of folding is that of collapse and packing of the Ω-loop on to the main body of the protein. 相似文献
11.
ERKs are the point of divergence of PKA and PKC activation by PTHrP in human skin fibroblasts 总被引:3,自引:0,他引:3
Fortino V Torricelli C Gardi C Valacchi G Rossi Paccani S Maioli E 《Cellular and molecular life sciences : CMLS》2002,59(12):2165-2171
Parathyroid hormone-related peptide (PTHrP) receptors, coupled to trimeric G proteins, operate in most target cells through
at least three different transduction routes: Gαs-mediated stimulation of adenylylcyclase (AC), Gαq-mediated activation of
phospholipase Cβ (PLC) and mitogen-activated protein kinase (MAPK) activation. In this study we investigated the relative
role of different pathways in human skin fibroblast prolifera-tion. Using chemical inhibitors and activators of signal transduction,
we demonstrated that: (i) AC/cAMP and PLC/1,4,5 inositol triphosphate/diacylglycerol second-messenger systems are simultaneously
activated following PTHrP binding to its receptors; (ii) the mitogenic response to PTHrP derives from a balance between two
counteracting pathways – an activating route mediated by protein kinase C (PKC) and an inhibitory route mediated by protein
kinase A (PKA); (iii) PTHrP mitogenic effects are largely dependent on MAPKs, whose activity can be modulate
d by both PKA and PKC. Our results indicate that MAPKs are common targets of both transduction routes and, at the same time,
their point of divergence in mediating PTHrP dual and opposite mitogenic effects.
Received 2 August 2002; received after revision 10 September 2002; accepted 18 October 2002
RID="*"
ID="*"Corresponding author. 相似文献
12.
Recent discoveries revealing that carbohydrate modifications play critical roles in a wide variety of biological processes
have brought wide recognition to the field of glycobiology. Growing attention has focused on the function of unusual O-linked carbohydrate modifications such as O-fucose. O-fucose modifications have been described in several different protein contexts, including epidermal growth factor-like repeats
and thrombospondin type 1 repeats. The O-fucose modifications on thrombospondin type 1 repeats have only recently been described, but the site of modification occurs
in a region proposed to play a role in cell adhesion. O-fucose modifications on epidermal growth factor-like repeats have been described as important players in several signal transduction
systems. For instance, Notch, a cell-surface signaling receptor required for many developmental events, bears multiple O-fucose saccharides on the epidermal growth factor-like repeat of its extracellular domain. The O-fucose moieties serve as a substrate for the β1,3 N-acetylglucosaminyltransferase activity of Fringe, a known modifier of Notch function. The alteration of O-fucose structures by Fringe influences the ability of Notch ligands to activate the receptor and provides a means to regulate
Notch signaling. Thus, O-fucose and Fringe provide a clear example of how carbohydrate modifications can have direct functional consequences on the
proteins they modify.
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ID="*"Corresponding author. 相似文献
13.
Cyanovirin-N: a sugar-binding antiviral protein with a new twist 总被引:7,自引:0,他引:7
Cyanovirin-N (CV-N), an 11-kDa protein from the cyanobacterium Nostoc ellipsosporum, is a highly potent virucidal agent that has generated interest as a lead natural product for the prevention and chemotherapy
of human immunodeficiency virus infection. The antiviral activity of CV-N is mediated through specific, high-affinity interactions
with the viral surface envelope glycoproteins. A number of structures of wild-type, mutant and sequence-shuffled CV-N have
been solved by nuclear magnetic resonance and crystallography, showing that the protein exists as either a quasi-symmetric
two-domain monomer or a domain-swapped dimer. Structures of several complexes of CV-N with oligosaccharides help in explaining
the unique mode of high-affinity binding of these molecules to both forms of CV-N.
RID="*"
ID="*"Corresponding author. 相似文献
14.
Anti-DNA antibodies: aspects of structure and pathogenicity 总被引:4,自引:0,他引:4
Anti-DNA antibodies contribute to the pathology of systemic lupus erythematosus. Their depositon in tissue lesions could
result from localization of preformed immune complexes of antibodies with DNA or nucleosomes, or from cross-reaction of anti-DNA
antibodies directly with tissue proteins. Structural analyses contribute to understanding their pathogenic potential. Primary
structures of lupus immunoglobulin G double-stranded DNA-binding autoantibodies are determined by immunoglobulin genes with
mutated variable region segments, indicative of selection by immunizing antigen. Arginine, lysine and asparagine residues
in complementarity-determining region favor DNA binding. Heavy-chain variable regions make major contributions to DNA binding;
affinity and specificity of binding are modulated or can be abrogated by the light-chain variable domain. Crytallographic
structure is known for a few antibody-DNA complexes and several ligand-free Fab fragments. Computer modeling supplements this
limited information. Structural information of lupus antibody interactions with both DNA and cross-reacting molecules will
support use of ligands to inhibit tissue deposition of the antibodies and prevent lesion formation in lupus.
Received 4 July 2002; accepted 23 July 2002
RID="*"
ID="*"Corresponding author. 相似文献
15.
Studies in the past years have implicated multispan transmembrane transport molecules of the ATP binding cassette (ABC) transporter
family in cellular lipid export processes. The prototypic ABC transporter ABCA1 has recently been demonstrated to act as a
major facilitator of cellular cholesterol and phospholipid export. Moreover, the transporter ABCA4 (ABCR) plays a pivotal
role in retinaldehyde processing, and ABCA3 has recently implicated in lung surfactant processing. These pioneering observations
have directed considerable attention to the A subfamily of ABC proteins. ABCA2 is the codefining member of the ABC A-transporter
subclass. Although known for some time, it was not until recently that its complete molecular structure was established. Unlike
other ABC A-subfamily members, ABCA2 is predominantly expressed in the brain and neural tissues. The unique expression profile
together with available structural data suggest roles for this largest known ABC protein in neural transmembrane lipid export.
Received 31 January 2002; received after revision 11 March 2002; accepted 11 March 2002 相似文献
16.
A role for <Emphasis Type="Italic">N</Emphasis>-acetylglucosamine as a nutrient sensor and mediator of insulin resistance 总被引:4,自引:0,他引:4
The ability to regulate energy balance at both the cellular and whole body level is an essential process of life. As western
society has shifted to a higher caloric diet and more sedentary lifestyle, the incidence of type 2 diabetes (non-insulin-dependent
diabetes mellitus) has increased to epidemic proportions. Thus, type 2 diabetes has been described as a disease of 'chronic
overnutrition'. There are abundant data to support the relationship between nutrient availability and insulin action. However,
there have been multiple hypotheses and debates as to the mechanism by which nutrient availability modulates insulin signaling
and how excess nutrients lead to insulin resistance. One well-established pathway for nutrient sensing is the hexosamine biosynthetic
pathway (HSP), which produces the acetylated aminosugar nucleotide uridine 5′-diphospho-N-acetylglucosamine (UDP-GlcNAc) as its end product. Since UDP-GlcNAc is the donor substrate for modification of nucleocytoplasmic
proteins at serine and threonine residues with N-acetylglucosamine (O-GlcNAc), the possibility of this posttranslational modification serving as the nutrient sensor has been proposed. We have
recently directly tested this model in adipocytes by examining the effect of elevated levels of O-GlcNAc on insulin-stimulated glucose uptake. In this review, we summarize the existing work that implicates the HSP and O-GlcNAc modification as nutrient sensors and regulators of insulin signaling.
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17.
This review begins with a general presentation of the new paradigm of drug discovery, with its emphasis on the rapid identification
and elimination of compounds with unsuitable physicochemical and pharmacokinetic properties. The focus of the paper is on
the various experimental methods used to determine such key physicochemical properties as ionization, lipophilicity and distribution
in isotropic and anisotropic systems, solubility, and permeability across artificial membranes. Both traditional and high-throughput
methods are presented and their limits highlighted. The text concludes with the trade-off between quantity/speed in high-throughput
screening techniques versus greater data quality in the more labor-intensive methods.
Received 23 April 2002; received after revision 25 June 2002; accepted 11 July 2002
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ID="*"Corresponding author. 相似文献
18.
Walter S 《Cellular and molecular life sciences : CMLS》2002,59(10):1589-1597
The Escherichia coli proteins GroEL and GroES were the first chaperones to be studied in detail and have thus become a role model for assisted protein folding in general. A wealth of both structural and functional data on the GroE system has been accumulated over the past years, enabling us now to understand the basic principles of how this fascinating protein-folding machine accomplishes its task. According to the current model, GroE processes a nonnative polypeptide in a cycle consisting of three steps. First, the polypeptide substrate is captured by GroEL. Upon binding of the co-chaperone GroES and ATP, the substrate is then discharged into a unique microenvironment inside of the chaperone, which promotes productive folding. After hydrolysis of ATP, the polypeptide is released into solution. Moreover, GroE may actively increase the folding efficiency, e.g. by unfolding of misfolded protein molecules. The mechanisms underlying these features, however, are yet not well characterized. 相似文献
19.
Microtubule associated protein tau binds to double-stranded but not single-stranded DNA 总被引:3,自引:0,他引:3
Hua Q He RQ Haque N Qu MH del Carmen Alonso A Grundke-Iqbal I Iqbal K 《Cellular and molecular life sciences : CMLS》2003,60(2):413-421
Tau, a major microtubule-associated protein of the neuron, which is known to promote the assembly of and to stabilize microtubules,
has also been seen associated with chromatin in neuronal cell lines, but its role in this subcellular compartment is still
unknown. In this study, the binding of tau to DNA was investigated using the electrophoretic mobility shift assay. Using polynucleotide
as probe, we found that tau bound to double-stranded but not to single-stranded DNA. Formation of tau-polynucleotide complex
was disrupted by alkaline pH and a high concentration of NaCl, but was not affected by dithiothreitol. Electron microscopy
revealed that the protein associated with the nucleic acid in a necklacelike manner. DNA-cellulose chromatography and radioimmunodot-blot
analyses showed that calf thymus histones VI-S, VII-S and VIII-S could replace both recombinant human brain tau352 (tau-23) and tau441 (tau-40) from DNA. Thus, tau appears to bind to DNA reversibly in the presence of histones.
Received 24 November 2002; received after revision 28 December 2002; accepted 30 December 2002
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ID="*"Corresponding author. 相似文献
20.
The superoxide-generating NADPH oxidase: structural aspects and activation mechanism 总被引:31,自引:0,他引:31
Vignais PV 《Cellular and molecular life sciences : CMLS》2002,59(9):1428-1459
Flavocytochrome b
558
is the catalytic core of the respiratory-burst oxidase, an enzyme complex that catalyzes the NADPH-dependent reduction of
O2 into the superoxide anion O2
- in phagocytic cells. Flavocytochrome b
558
is anchored in the plasma membrane. It is a heterodimer that consists of a large glycoprotein gp91phox (phox for phagocyte oxidase) (β subunit) and a small protein p22phox (α subunit). The other components of the respiratory-burst oxidase are water-soluble
proteins of cytosolic origin, namely p67phox, p47phox, p40phox and Rac. Upon cell stimulation, they assemble with the membrane-bound
flavocytochrome b
558
which becomes activated and generates O2
-. A defect in any of the genes encoding gp91phox, p22phox, p67phox or p47phox results in chronic granulomatous disease, a
genetic disorder characterized by severe and recurrent infections, illustrating the role of O2
- and the derived metabolites H2O2 and HOCl in host defense against invading microorganisms. The electron carriers, FAD and hemes b, and the binding site for NADPH are confined to the gp91phox subunit of flavocytochrome b
558
. The p22phox subunit serves as a docking site for the cytosolic phox proteins. This review provides an overview of current
knowledge on the structural organization of the O2
--generating flavocytochrome b
558
, its kinetics, its mechanism of activation and the regulation of its biosynthesis. Homologues of gp91phox, called Nox and
Duox, are present in a large variety of non-phagocytic cells. They exhibit modest O2
--generating oxidase activity, and some act as proton channels. Their role in various aspects of signal transduction is currently
under investigation and is briefly discussed.
Received 28 May 2002; received after revision 20 June 2002; accepted 24 June 2002 相似文献