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PubMed2003

The COP9 signalosome-like complex in S. cerevisiae and links to other PCI complexes.

The COP9 signalosome (CSN), the lid subcomplex of the proteasome and translational initiation factor 3 (eIF3) share structural similarities and are often referred to as the PCI family of complexes. In multicellular eukaryotes, the CSN is highly conserved as an 8-subunit complex but in Saccharomyces cerevisiae the complex is rather divergent. We further characterize the composition and properties of the CSN in budding yeast and its interactions with these related complexes. Using the generalized profile method we identified CSN candidates, four with PCI domains: Csn9, Csn10, Pci8/Csn11, and Csn12, and one with an MPN domain, Csn5/Rri1. These proteins and an additional interactor, Csi1, were tested for pairwise interactions by yeast two-hybrid and were found to form a cluster surrounding Csn12. Csn5 and Csn12 cofractionate in a complexed form with an apparent molecular weight of roughly 250kDa. However, Csn5 migrates as a monomer in Deltacsn12 supporting the pivotal role of Csn12 in stabilizing the complex. Confocal fluorescence microscopy detects GFP-tagged Csn5 preferentially in the nucleus, whereas in absence of Csn12, Csn10, Pci8/Csn11, or Csi1, Csn5 is delocalized throughout the cell, indicating that multiple subunits are required for nuclear localization of Csn5. Two CSN subunits, Csn9 and Csi1, interact with the proteasome lid subunit Rpn5. Pci8/Csn11 has previously been shown to interact with eIF3. Together, these results point to a network of interactions between these three structurally similar, yet functionally diverse, complexes.

Amino Acid Sequence↗
PubMedDate not supplied

Evaluation of Syngene DNA-DNA probe assays for the identification of the Mycobacterium tuberculosis complex and the Mycobacterium avium complex.

Two hundred mycobacterial cultures were used to evaluate two alkaline-phosphatase-labeled DNA probe (SNAP) kits developed by Syngene (San Diego, CA) for identification of Mycobacterium tuberculosis complex and M. avium complex. The M. tuberculosis complex SNAP probe, when compared with standard biochemical identification tests, gave results that were in agreement at 100% sensitivity and 98.7% specificity. Ninety-nine M. avium complex strains that were previously tested by the Gen-Probe M. avium complex probe assays and mycolic acid analysis were included to evaluate the M. avium complex SNAP assay which contained three probes, A (avium), I (intracellulare), and X. Eight strains identified as members of the M. avium complex by biochemical tests did not react with the three SNAP probes. These strains were also negative by the Gen-Probe assays. However, 23 strains identified as M. avium complex by biochemical tests and mycolic acid analysis and negative with the Gen-Probe assays gave positive results with the X probe and negative results with the A and I probes of the SNAP assay.

Alkaline Phosphatase↗
PubMed1982

Occupancy of phosphorylation sites in pyruvate dehydrogenase phosphate complex in rat heart in vivo. Relation to proportion of inactive complex and rate of re-activation by phosphatase.

The [gamma-32P]ATP-back-titration method of estimating occupancy in vivo of the three phosphorylation sites in the pyruvate dehydrogenase complex was improved in precision by specific analysis with trypsin/formic acid, by more effective prevention of site-2 dephosphorylation during purification with NaF, and by other refinements. Disproportionation of phosphorylated complexes during purification was excluded. With this improved method it was shown that the relationship between occupancy of sites and the proportion of complex in the inactive form in rat heart in vivo is closely similar to that measured directly in heart mitochondria by incorporation of [32P]Pi. In the heart in vivo (as in mitochondria), occupancy of site 1 correlated linearly with the proportion of inactive complex. Occupancy of sites 2 and 3 only approached equivalence to that of site 1 when 99% of the complex was inactive (starved or diabetic rats). When 70% or less of the complex was inactive (resting or exercising fed normal rats), occupancy of sites 2 and 3 was minimal (3 less than 2) relative to site 1. The initial rate of re-activation by phosphatase of phosphorylated complex from hearts of resting or exercising fed normal rats was approximately three times that of complex from 48 h-starved rats.

Adenosine Triphosphate↗
PubMed2000

Kinetic properties of the 2-oxoglutarate dehydrogenase complex from Azotobacter vinelandii evidence for the formation of a precatalytic complex with 2-oxoglutarate.

The 2-oxoglutarate dehydrogenase complex was purified from Azotobacter vinelandii. The complex consists of three components, 2-oxoglutarate dehydrogenase/decarboxylase (E1o), lipoate succinyltransferase (E2o) and lipoamide dehydrogenase (E3). Upon purification, the E3 component dissociates partially from the complex. From reconstitution experiments, the Kd for E3 was found to be 26 nM, about 30 times higher than that for the pyruvate dehydrogenase complex. The Km values for the substrates 2-oxoglutarate, CoA and NAD+ were found to be 0.15, 0.014 and 0.17 mM, respectively. The system has a high specificity for 2-oxoglutarate, which is determined by the action of both E1o and E2o. Above 4 mM substrate inhibition is observed. From steady-state inhibition experiments with substrate analogs, two substrate-binding modes are revealed at different degrees of saturation of the enzyme with 2-oxoglutarate. At low substrate concentrations (10(-6) to 10(-5) M), the binding mainly depends on the interaction of the enzyme with the substrate carboxyl groups. At a higher degree of substrate saturation (10(-4) to 10(-3) M) the relative contribution of the 2-oxo group in the binding increases. A kinetic analysis points to a single binding site for a substrate analog under steady state conditions. Saturation of this site with an analog indicates that two kinetically different complexes are formed with 2-oxoglutarate in the course of catalysis. From competition studies with analogs it is concluded that one of these complexes is formed at the site that is sterically identical to the substrate inhibition site. The data obtained are represented by a minimal scheme that considers formation of a precatalytic complex SE between the substrate and E1o before the catalytic complex ES, in which the substrate is added to the thiamin diphosphate cofactor, is formed. The incorrect orientation of the substrate molecule in SE or the occupation of this site by analogs is supposed to cause substrate or analog inhibition, respectively.

Acyltransferases↗
PubMed2003

A defined protein-detergent-lipid complex for crystallization of integral membrane proteins: The cytochrome b6f complex of oxygenic photosynthesis.

The paucity of integral membrane protein structures creates a major bioinformatics gap, whose origin is the difficulty of crystallizing these detergent-solubilized proteins. The problem is particularly formidable for hetero-oligomeric integral membrane proteins, where crystallization is impeded by the heterogeneity and instability of the protein subunits and the small lateral pressure imposed by the detergent micelle envelope that surrounds the hydrophobic domain. In studies of the hetero (eight subunit)-dimeric 220,000 molecular weight cytochrome b(6)f complex, derived from the thermophilic cyanobacterium, Mastigocladus laminosus, crystals of the complex in an intact state could not be obtained from highly purified delipidated complex despite exhaustive screening. Crystals of proteolyzed complex could be obtained that grew very slowly and diffracted poorly. Addition to the purified lipid-depleted complex of a small amount of synthetic nonnative lipid, dioleolyl-phosphatidylcholine, resulted in a dramatic improvement in crystallization efficiency. Large crystals of the intact complex grew overnight, whose diffraction parameters are as follows: 94% complete at 3.40 A spacing; R(merge) = 8.8% (38.5%), space group, P6(1)22; and unit cell parameters, a = b = 156.3 A, c = 364.0 A, alpha = beta = 90 degrees, gamma = 120 degrees. It is proposed that the methodology of augmentation of a well-defined lipid-depleted integral membrane protein complex with synthetic nonnative lipid, which can provide conformational stability to the protein complex, may be of general use in the crystallization of integral membrane proteins.

Crystallization↗
PubMed1998

Analysis of Gag-specific cytotoxic T lymphocytes in simian immunodeficiency virus-infected rhesus monkeys by cell staining with a tetrameric major histocompatibility complex class I-peptide complex.

A tetrameric recombinant major histocompatibility complex (MHC) class I-peptide complex was used as a staining reagent in flow cytometric analyses to quantitate and define the phenotype of Gag-specific cytotoxic T lymphocytes (CTLs) in the peripheral blood of simian immunodeficiency virus macaque (SIVmac)-infected rhesus monkeys. The heavy chain of the rhesus monkey MHC class I molecule Mamu-A*01 and beta2-microglobulin were refolded in the presence of an SIVmac Gag synthetic peptide (p11C, C-M) representing the optimal nine-amino acid peptide of Mamu-A*01-restricted predominant CTL epitope to create a tetrameric Mamu-A*01/p11C, C-M complex. Tetrameric Mamu-A*01/p11C, C-M complex bound to T cells of SIVmac-infected, Mamu-A*01(+), but not uninfected, Mamu-A*01(+), or infected, Mamu-A*01(-) rhesus monkeys. Specific staining of peripheral blood mononuclear cells (PBMC) from SIVmac-infected, Mamu-A*01(+) rhesus monkeys was only found in the cluster of differentiation (CD)8alpha/beta+ T lymphocyte subset and the percentage of CD8alpha/beta+ T cells in the peripheral blood of four SIVmac-infected, Mamu-A*01+ rhesus monkeys staining with this complex ranged from 0.7 to 10.3%. Importantly, functional SIVmac Gag p11C-specific CTL activity was seen in sorted and expanded tetrameric Mamu-A*01/p11C, C-M complex-binding, but not nonbinding, CD8alpha/beta+ T cells. Furthermore, the percentage of CD8alpha/beta+ T cells binding this tetrameric Mamu-A*01/p11C, C-M complex correlated well with p11C-specific cytotoxic activity as measured in both bulk and limiting dilution effector frequency assays. Finally, phenotypic characterization of the cells binding this tetrameric complex indicated that this lymphocyte population is heterogeneous. These studies indicate the power of this approach for examining virus-specific CTLs in in vivo settings.

Animals↗
PubMed1991

Cell-type specific multiprotein complex formation over the c-fos serum response element in vivo: ternary complex formation is not required for the induction of c-fos.

At the serum response element (SRE) of the c-fos proto-oncogene a ternary complex with two proteins, ternary complex factor (p62TCF) and serum response factor (SRF) can be formed. Its formation has previously been suggested to be necessary for efficient induction of c-fos transcription by serum in mouse NIH 3T3 fibroblasts (1) and by phorbol esters, but not by serum, in mouse BALB/c 3T3 fibroblasts (2). It is shown here by genomic dimethyl sulfate (DMS) footprinting that this ternary complex is indeed formed in NIH 3T3 cells in vivo. However, cells were found, murine F9 teratocarcinoma stem cells, in which the pattern of protection and hyperreactivity is consistent with the absence of p62TCF in the protein complex in vivo, although inducibility of the endogenous c-fos gene is not impaired. Both in NIH 3T3 cells and in F9 cells a mutated c-fos promoter that binds SRF but fails to form a ternary complex, was inducible by serum and phorbol esters to the same extent as the wild-type promoter. The data suggest that ternary complex formation is not an absolute prerequisite for the transient induction of c-fos. Ternary complex formation rather appears to enhance overall promoter efficiency. A cell type specific component determines the formation of the multicomponent transcription factor complex in vivo.

Animals↗
PubMed1984

Binding and activation of the first complement component by soluble immune complexes: effect of complex size and composition.

The interaction between soluble immune complexes and the first component of complement (C1) was studied. Complexes were prepared from purified bovine thyroglobulin (BTg) or tetanus toxoid (TT) and immunospecific IgG antibodies. Purified human precursor C1 was incubated with dilutions of the preparations, and the inhibition of C1 haemolytic activity was determined as a measure of C1-binding. The activation of C1 was assessed by measuring the amount of C4 consumed by generated C1. The molar antibody/antigen (Ab/Ag) ratio of BTg--anti-BTg mixtures strongly influenced their C1-binding and C1-activating capacities: mixtures with high Ab/Ag ratios were by far the most efficient. On the other hand, the Ab/Ag ratio had only a limited influence on the activity of TT--anti-TT complexes. The effect of complex size was investigated by ultracentrifugation of antibody-antigen mixtures on calibrated sucrose density gradients followed by C1-binding and -activation experiments with the fractions obtained. For both types of immune complex, the C1-binding and -activating capacities increased markedly with increasing complex size. Thus, both the size and the Ab/Ag ratio of soluble immune complexes influence their capacity to activate the classical complement pathway. The effect of the Ab/Ag ratio, however, may also be dependent on the antigen molecule(s) present in the complexes.

Animals↗
PubMed2002

Mitochondrial import of the ADP/ATP carrier: the essential TIM complex of the intermembrane space is required for precursor release from the TOM complex.

The mitochondrial intermembrane space contains a protein complex essential for cell viability, the Tim9-Tim10 complex. This complex is required for the import of hydrophobic membrane proteins, such as the ADP/ATP carrier (AAC), into the inner membrane. Different views exist about the role played by the Tim9-Tim10 complex in translocation of the AAC precursor across the outer membrane. For this report we have generated a new tim10 yeast mutant that leads to a strong defect in AAC import into mitochondria. Thereby, for the first time, authentic AAC is stably arrested in the translocase complex of the outer membrane (TOM), as shown by antibody shift blue native electrophoresis. Surprisingly, AAC is still associated with the receptors Tom70 and Tom20 when the function of Tim10 is impaired. The nonessential Tim8-Tim13 complex of the intermembrane space is not involved in the transfer of AAC across the outer membrane. These results define a two-step mechanism for translocation of AAC across the outer membrane. The initial insertion of AAC into the import channel is independent of the function of Tim9-Tim10; however, completion of translocation across the outer membrane, including release from the TOM complex, requires a functional Tim9-Tim10 complex.

Intracellular Membranes↗
PubMed2001

Anti-interleukin 8 autoantibody: interleukin 8 complexes in the acute respiratory distress syndrome. Relationship between the complexes and clinical disease activity.

Increased levels of interleukin 8 (IL-8) are found in bronchoalveolar lavage (BAL) fluids from patients with the acute respiratory distress syndrome (ARDS). However, IL-8 is not an efficient predictor of the course of ARDS. Our prior studies demonstrated that IL-8 present in lung fluids from patients with ARDS is associated with anti-IL-8 autoantibodies (anti-IL-8:IL-8 complexes). These data led us to hypothesize that the complexes might better predict the development of acute lung injury. Accordingly, we measured concentrations of free and complexed IL-8 in BAL fluids from 19 patients at risk and 45 with established ARDS on Days 1, 3, 7, 14, and 21 after the onset of ARDS. The concentrations of anti-IL-8:IL-8 complexes in patients with ARDS on Day 1 were significantly higher than in patients at risk (p < 0.05). There was a significant association between anti-IL-8:IL-8 complex concentrations and the onset of ARDS (p = 0.03). Similarly, anti-IL-8:IL-8 complex concentrations were significantly higher in patients on Day 1 of ARDS who later died (p < 0.05), and the association between high anti-IL-8: IL-8 complex concentrations and the probability of dying was significant (p = 0.03). The presence of anti-IL-8:IL-8 complexes in BAL fluids of patients with ARDS is an important prognostic indicator for the development and outcome of ARDS.

Adolescent↗
PubMed2000

The something about silencing protein, Sas3, is the catalytic subunit of NuA3, a yTAF(II)30-containing HAT complex that interacts with the Spt16 subunit of the yeast CP (Cdc68/Pob3)-FACT complex.

We have purified and characterized a Gcn5-independent nucleosomal histone H3 HAT complex, NuA3 (Nucleosomal Acetyltransferase of histone H3). Peptide sequencing of proteins from the purified NuA3 complex identified Sas3 as the catalytic HAT subunit of the complex. Sas3 is the yeast homolog of the human MOZ oncogene. Sas3 is required for both the HAT activity and the integrity of the NuA3 complex. In addition, NuA3 contains the TBP- associated factor, yTAF(II)30, which is also a component of the TFIID, TFIIF, and SWI/SNF complexes. Sas3 mediates interaction of the NuA3 complex with Spt16 both in vivo and in vitro. Spt16 functions as a component of the yeast CP (Cdc68/Pob3) and mammalian FACT (facilitates chromatin transcription) complexes, which are involved in transcription elongation and DNA replication. This interaction suggests that the NuA3 complex might function in concert with FACT-CP to stimulate transcription or replication elongation through nucleosomes by providing a coupled acetyltransferase activity.

Acetyltransferases↗
PubMed1987

Immunoregulation by antigen/antibody complexes. I. Specific immunosuppression induced in vivo with immune complexes formed in antibody excess.

Specific immune complexes, prepared at different ratios of antibody to antigen, were examined for their effects on the antibody response of BALB/c mice to the cell wall polysaccharide antigen (PnC) extracted from Streptococcus pneumonia R36a. Mice immunized with complexes formed in antigen excess developed a PnC-specific antibody response that was equivalent to that in mice injected with free antigen. On the other hand, mice injected with complexes formed in antibody excess developed very little PnC-specific antibody. Furthermore, administration of immune complexes (formed in antibody excess) resulted in suppression of the response to an immunogenic dose of PnC given concurrently or 1 day after injection of immune complexes but not when the antigen was given 1 day before injection of the immune complexes. Injections of free antibody (TEPC-15) also resulted in suppression of the response to antigenic challenge; however, suppression was greatest when the antibody was injected concurrently with the antigen, suggesting that the suppression was mediated through the formation of immune complexes in vivo. The suppression appears to be specific for the antigen (PnC), since in mice injected with TEPC-15/PnC complexes (formed in antibody excess) and challenged with PnC coupled to sheep RBC, only the response to PnC was suppressed.

Animals↗
PubMed1980

The value of three immune complex assays in the management of systemic lupus erythematosus: an assessment of immune complex levels, size and immunochemical properties in relation to disease activity and manifestations.

Sixteen patients with systemic lupus erythematosus, fourteen with renal involvement have been studied over a 30-month period. Circulating immune complex levels have been assayed by three techniques. The results of tests on 141 sequential sera suggest that the three assays detected overlapping populations of the range of complexes present. Immune complex levels are shown to be good markers of disease activity and certain immunochemical properties of the complexes emerged as better markers than others. Immune complex size is a more important determinant of disease manifestation than are overall immune complex levels. High doses of intravenous methyl prednisolone, which did not reduce overall complex levels, reduced levels of those complexes (molecular weight 600,000-900,000 Daltons) associated with renal involvement.

Antibodies↗
PubMed1995

Low platelet mitochondrial complex I and complex II/III activity in early untreated Parkinson's disease.

Following the discovery of inhibition of electron transport complex 1 by the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), which produces a parkinsonian syndrome in humans, monkeys, and mice, several laboratories have reported abnormalities of complex I and other electron transport complexes (ETCs) in various tissues from patients with Parkinson's disease (PD). Criticism of the significance of these findings in the etiology of PD has centered on whether drug treatments or the debilitation of the disease process itself produced the low ETC activities. We present results from a blinded study of platelet mitochondrial ETC activities in 18 early untreated PD patients and 18 age- and sex-matched controls and in 13 spousal controls. Lower complex I activity in platelet mitochondria of PD patients was seen in early untreated disease and thus cannot be due to debilitation or drug therapy. Home environmental factors seem an unlikely explanation for the reduced complex I activity in PD patients but have not been excluded. Complex II/III activity was also reduced by 20% in PD compared with age-/sex-matched controls. The low complex I and II/III activities in platelet mitochondria appear to be related to the etiology of PD.

Adult↗
PubMed1988

Characterization of the manganese O2-evolving complex and the iron-quinone acceptor complex in photosystem II from a thermophilic cyanobacterium by electron paramagnetic resonance and X-ray absorption spectroscopy.

The Mn donor complex in the S1 and S2 states and the iron-quinone acceptor complex (Fe2+-Q) in O2-evolving photosystem II (PS II) preparations from a thermophilic cyanobacterium, Synechococcus sp., have been studied with X-ray absorption spectroscopy and electron paramagnetic resonance (EPR). Illumination of these preparations at 220-240 K results in formation of a multiline EPR signal very similar to that assigned to a Mn S2 species observed in spinach PS II, together with g = 1.8 and 1.9 EPR signals similar to the Fe2+-QA- acceptor signals seen in spinach PS II. Illumination at 110-160 K does not produce the g = 1.8 or 1.9 EPR signals, nor the multiline or g = 4.1 EPR signals associated with the S2 state of PS II in spinach; however, a signal which peaks at g = 1.6 appears. The most probable assignment of this signal is an altered configuration of the Fe2+-QA- complex. In addition, no donor signal was seen upon warming the 140 K illuminated sample to 215 K. Following continuous illumination at temperatures between 140 and 215 K, the average X-ray absorption Mn K-edge inflection energy changes from 6550 eV for a dark-adapted (S1) sample to 6551 eV for the illuminated (S2) sample. The shift in edge inflection energy indicates an oxidation of Mn, and the absolute edge inflection energies indicate an average Mn oxidation state higher than Mn(II). Upon illumination a significant change was observed in the shape of the features associated with 1s to 3d transitions. The S1 spectrum resembles those of Mn(III) complexes, and the S2 spectrum resembles those of Mn(IV) complexes. The extended X-ray absorption fine structure (EXAFS) spectrum of the Mn complex is similar in the S1 and S2 states. Simulations indicate O or N ligands at 1.75 +/- 0.05 A, transition metal neighbor(s) at 2.73 +/- 0.05 A, which are assumed to be Mn, and terminal ligands which are probably N and O at a range of distances around 2.2 A. The Mn-O bond length of 1.75 A and the transition metal at 2.7 A indicate the presence of a di-mu-oxo-bridged Mn structure. Simulations indicate that a symmetric tetranuclear cluster is unlikely to be present, while binuclear, trinuclear, or highly distorted tetranuclear structures are possible. The striking similarity of these results to those from spinach PS II suggests that the structure of the Mn complex is largely conserved across evolutionarily diverse O2-evolving photosynthetic species.

Chlorophyll↗
PubMed2001

Mitochondrial adaptations to NaCl. Complex I is protected by anti-oxidants and small heat shock proteins, whereas complex II is protected by proline and betaine.

High soil sodium (Na) is a common stress in natural and agricultural systems. Roots are usually the first tissues exposed to Na stress and Na stress-related impairment of mitochondrial function is likely to be particularly important in roots. However, neither the effects of NaCl on mitochondrial function, nor its protection by several potential adaptive mechanisms, have been well studied. This study investigated the effects of NaCl stress on maize (Zea mays) mitochondrial electron transport and its relative protection by osmoprotectants (proline, betaine, and sucrose), antioxidants (ascorbate, glutathione, and alpha-tocopherol), antioxidant enzymes (catalase and Cu/Zn-superoxide dismutase), and mitochondrial small heat shock proteins (sHsps). We demonstrate that Complex I electron transport is protected by antioxidants and sHsps, but not osmoprotectants, whereas Complex II is protected only by low concentrations of proline and betaine. These results indicate that NaCl stress damaged Complex I via oxidative stress and suggests that sHsps may protect Complex I as antioxidants, but NaCl damaged Complex II directly. This is the first study to demonstrate that NaCl stress differentially affects Complex I and II in plants and that protection of Complex I and II during NaCl stress is achieved by different mechanisms.

Adaptation, Physiological↗
PubMed2000

Complexation of polyvalent cyclodextrin ions with oppositely charged guests: entropically favorable complexation due to dehydration.

Thermodynamic parameters for complexation of polyvalent cyclodextrin (CD) cation and anion with oppositely charged guests have been determined in D2O containing 0.02 M NaCl by means of 1H-NMR spectroscopy. Protonated heptakis(6-amino-6-deoxy)-beta-CD (per-NH3+-beta-CD) forms stable inclusion complexes with monovalent guest anions. The enthalpy (deltaH) and entropy changes (deltaS) for complexation of per-NH3+-beta-CD with p-methylbenzoate anion (p-CH3-Ph-CO2-) are 3.8 +/- 0.7 kJ mol(-1) and 88.6 +/- 2.2 J mol(-1) K(-1), respectively. The deltaH and deltaS values for the native beta-CD-p-CH3-Ph-CO2- system are -8.6 +/- 0.1 kJ mol(-1) and 15.3 +/- 0.7 J mol(-1) K(-1), respectively. The thermodynamic parameters clearly indicate that dehydration from both the host and guest ions accounts for the entropic gain in inclusion process of p-CH3-Ph-CO2- into the per-NH3+-beta-CD cavity. The fact that the neutral guests such as 2,6-dihydroxynaphthalene and p-methylbenzyl alcohol hardly form the complexes with per-NH3+-beta-CD exhibits that van der Waals and/or hydrophobic interactions do not cause the complexation of the polyvalent CD cation with the monovalent anion. The acetate anion is not included into the per-NH3+-beta-CD cavity, while the butanoate and hexanoate anions form the inclusion complexes. The complexation of the alkanoate anions is entropically dominated. Judging from these results, it may be concluded that Coulomb interactions cooperated with inclusion are required for realizing the large entropic gain due to extended dehydration. Entropically favorable complexation was also observed for the anionic CD-cationic guest system. The present study might present a general mechanism for ion pairing in water.

Anions↗
PubMed1995

Identification of a complex between centrin and heat shock proteins in CSF-arrested Xenopus oocytes and dissociation of the complex following oocyte activation.

Coimmunoprecipitation experiments using a monoclonal anti-centrin antibody (20H5) and cytostatic factor (CSF)-arrested Xenopus oocyte extracts specifically precipitates oocyte centrin (20-kDa) and two associated proteins of 70- and 90-kDa. Microsequence analysis of a tryptic peptide fragment of the 70-kDa protein reveals 100% identity with a 13-amino-acid peptide sequence from Xenopus heat shock protein hsp-70. Western blot analysis of immunoprecipitates using anti-hsp monoclonal antibodies (N27 and AC-88) confirms the identity of the 70-kDa protein as hsp-70 and identifies the 90-kDa protein as hsp-90. The centrin/hsp complex is also immunoprecipitated when anti-hsp-70 or anti-hsp-90 monoclonal antibodies (BB70 and 4F3, respectively) are used as primary antibodies during immunoprecipitation. The centrin/hsp complex is sensitive to pH and Ca2+ concentration. The complex shows differential dissociation of hsp-70 and hsp-90 under a variety of conditions, suggesting that each hsp can bind to centrin independently of the other. When oocytes are first activated by electric shock or ionophore treatment, followed by immunoprecipitation using anti-centrin monoclonal antibody 20H5, centrin precipitates with significantly reduced levels of hsp-70 in the complex, and these complexes contain no apparent hsp-90. We conclude that, in CSF-arrested oocytes, the centrosomal protein, centrin, is associated as a complex with the heat shock proteins, hsp-70 and hsp-90, and that this complex dissociates upon activation of the oocyte. The functional consequences of the formation of complexes between centrin and these hsps are unknown. However, based on the roles that have been defined for heat shock proteins in other systems, several possibilities are suggested.

Amino Acid Sequence↗