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PubMed1975

Effects of denaturants on the sweet-tasting protein monellin.

Effects of the denaturants urea and guanidine-HCl on the sweet-tasting protein monellin have been studied. The pH at which monellin is initially treated with denaturant is an important factor in retention of sweetness, but the pH maintained during subsequent removal of denaturant by dialysis has no effect on activity. Recovery of sweetness of denaturant-treated monellin is favored when denaturation occurs at acid pH. Monellin treated with either 6 M guanidine-HCl or 8 M urea at acid pH retains all of its sweetness following removal of denaturant, but urea treatment at neutral pH leads to some irreversible loss of sweetness. Monellin precipitates from solution under some conditions during removal of denaturant by dialysis, and the precipitated protein is no longer sweet. Precipitation is least under acid conditions. Aggregated protein was demonstrated by gel filtration chromatography. The single sulfhydryl group of monellin was not demonstrable in the precipitated protein, having apparently become oxidized during denaturation and formation of the aggregated protein. The data support the hypothesis that the tertiary structure is important in the ability of monellin to elicit a sweet sensation.

Guanidines↗

PubMed1977

Assembly of tobacco mosaic virus in vitro: elongation of partially reconstituted RNA.

It was reported that the rate of elongation of partially reconstituted RNA, if prepared without centrifugation, showed dependency upon the state of protein aggregation like that found when free RNA was used as the nucleic acid source [Butler, P. J. G. (1974) J. Mol. Biol. 82, 333-341]. Butler concluded from this result that disks are the kinetically favored protein source for the elongation of the tobacco mosaic virus rod. We show that partially reconstituted RNA prepared without centrifugation always contains a significant amount of free RNA and conclude that the dependency of its elongation rate upon the state of protein aggregation is due to contamination of his partially reconstituted RNA preparation by free RNA. The elongation rate of partially reconstituted RNA, which had been pelleted and contained no free RNA, was found to be about the same regardless of the state of aggregation of the added protein.

Centrifugation, Density Gradient↗

PubMed1975

Circular dichroism and gel filtration behavior of subtilisin enzymes in concentrated solutions of guanidine hydrochloride.

The circular dichroism of diisopropylphosphorylsubtilisins Novo and Carlsberg in both the near- and farultraviolet spectral regions is unaltered by concentrations of guanidine hydrochloride as high as 4 M at neutral pH. At concentrations of guanidine hydrochloride greater than 4 M slow irreversible time-dependent changes, apparently obeying second-order kinetics, are evident in both the near- and far-ultraviolet circular dichroism of these enzymes. Gel filtration studies of inactivated subtilisin enzymes reveal the circular dichroism changes to be accompained by the appearance of aggregated protein material. The changes in circular dichroism and the production of associated subtilisin species are sensitive to protein concentration, denaturant concentrations, and pH. The circular dichroism of active subtilisins Novo and Carlsberg in guanidine hydrochloride exhibits irreversible changes similar to those observed for the inactivated subtilisins. Aggregated protein material is also formed initially in the presence of guanidine hydrochloride, but is rapidly autolyzed to low molecular weight fragments.

Binding Sites↗

PubMedDate not supplied

[Radiation-induced aggregation of proteins: binding of amino acids to myoglobin (author's transl)].

When myoglobin is irradiated in the presence of amino acids, the most radiation-reactive species, like the aromatic and sulfur-containing amino acids, will bind preferentially to the protein. The radiation-induced binding is strongly dependent on the concentration of protein and amino acid. Subsequent to irradiation of myoglobin in the presence of radioactively labelled tryptophan followed by tryptic hydrolysis, only a single radioactive spot was detected on the fingerprint. The binding of amino acids is thus not randomly distributed over the protein molecule but occurs at specific reactive sites.

Amino Acids↗

PubMed2025

A rare genetic variant confers resistance to neurodegeneration across multiple neurological disorders by augmenting selective autophagy.

The study of disease modifiers is a powerful way to identify patho-mechanisms associated with disease. Using the strong genetic traits of Huntington's disease (HD), we identified a rare, single-nucleotide polymorphism (SNP) in WDFY3 associated with a delayed age of onset of up to 23 years. Remarkably, the introduction of the orthologous SNP into mice recapitulates this neuroprotection, significantly delaying neuropathological and behavioral dysfunction in two models of HD. The SNP increases expression of the protein autophagy-linked Fab1, YOTB, Vac1, and EEA1 (FYVE) protein (Alfy), an autophagy adaptor protein for the clearance of aggregated proteins, whose ectopic overexpression is sufficient to capture the neuroprotective effects of the variant. Increasing Alfy expression protects not only against HD but also against the toxicity due to phospho-α-synuclein and AT8-positive accumulation. By combining human and mouse genetics, we have uncovered a pathway that protects against multiple proteinopathies, revealing a much-sought-after, shared therapeutic target across a broad range of neurodegenerative diseases.

Animals↗

PubMed1976

Assembly of tobacco mosaic virus.

The assembly of tobacco mosaic virus requires the presence of a particular protein aggregate, the disk. During the nucleation, a specific region of the RNA interacts with a single disk, to bring about a necessarily cooperative transition from the paired two-layer structure to a short segment of nucleo-protein helix. There is a high selectivity for this region of the TMV RNA, because of the many nucleotides bound at once, and other nucleotide sequences appear only to bind by a different mechanism. Elongation of the nucleated rods can continue with either further disks or the less aggregated 'A-protein' as the protein source, but the continued cooperativity inherent with disks would have some advantages. The rates of the two processes have been separately determined and growth is faster when disks are still present. New experiments show that the breakdown of disks to yield A-protein is relatively slow and it is concluded that virus growth from disks could not proceed through a prior breakdown in solution, but must involve the direct interaction of the disk with the growing nucleoprotein rod. The detailed mechanism of disk addition is not understood but it may involve a directed breakdown, since there is also evidence for the existence of a non-equilibrium form of A-protein which has aggregation kinetics distinct from those of equilibrium A-protein. Some implications for the general assembly pathways of viruses both of the specificity and of the assembly/disassembly cycle during the viral infection are considered.

Kinetics↗

PubMed1977

Spontaneous, reversible protein cross-linking in the human erythrocyte membrane. Temperature and pH dependence.

Changes in pH significantly affect the morphology and physical properties of red cell membranes. We have explored the molecular basis for these phenomena by characterizing the pattern of protein disulfide cross-linkages formed spontaneously in ghost exposed to acid pH or elevated temperature (37 degrees C). Protein aggregation was analyzed by two-dimensional polyacrylamide gel electrophoresis in sodium dodecyl sulfate. incubation of ghosts at pH 4.0 to 5.5 (0-4 degrees C) yielded (i) complexes of spectrin and band 3, (ii) complexes of actin and band 3, (iii) band 3 complexes, i.e. dimer and trimer, and (iv) heterogeneous aggregates involving spectrin, band 3, band 4.2, and actin in varying proportions. Aggregation was maximal near the isoelectric points of the major membrane proteins, and appeared to reflect (i) the aggregation of intramembrane particles including band 3 and (ii) more intimate contact between spectrin-actin meshwork and band 3.

Actins↗

PubMed2026

Riboregulation: a non-canonical tau function.

Almost since its discovery, tau protein has perplexed scientists and clinicians with its varied roles in physiology as well as its appearance as phosphorylated protein aggregates of various structures in many neurodegenerative diseases. Tau plays a role in microtubule stabilization, but from the earliest of studies, tau has also been observed to bind to RNA, with recent research suggesting tau has a higher affinity for some RNA species compared to microtubules. In the context of disease, tau dysfunction potentiates disruptions to RNA metabolism, including the perturbation of mRNA splicing, impairment of translation, de-repression of transposable elements, and alteration of RNA export and degradation. Tau aggregates directly sequester diverse RNA species and RNA binding proteins. Emerging evidence reinforces the characterization of tau as an RNA binding protein, highlighting questions about both the physiological and disease-related functions of this direct RNA binding. The disparate structure of tau in normal and various disease states makes teasing apart the various impacts on RNA and regulation a more difficult puzzle requiring future study. In this review, we summarize the evidence for tau's role in RNA biology, including as an RNA binding protein.

tau Proteins↗

PubMed1976

Testosterone-binding protein in reproductive tracts of fetal rats.

Testosterone-binding proteins may mediate the induction of Wolffian duct differentiation by testicular testosterone. The presence of such protein(s) was sought in reproductive tracts of 14.5-21.5-day-old fetal rats. Supernatant fractions (127,000 x g) were equilibrated with [3H]T) +/- radioinert testosterone in Tris - HCl:EDTA buffer, pH 7.4, (approximately 0.1 mg protein/0.5 ml) at 4 C for 16 hours. Bound and free (3H)T were separated by charcoaldextran adsorption or Sephadex G-100 gel filtration. The results with 14.5-15.0-day-old tracts were: a) specific binding to protein was saturated with increasing (3H)T concentration; b) Scatchard plot analysis indicated the presence of a single class of binding sites with high affinity (apparent Kd = 2 nM) and limited capacity (approximately 16 fmol/mg protein) for (3H)T; c) specific uptake was limited to (3H)T and (3H)5 alpha-dihydrotestosterone; d) (3H)T uptake by the tract supernatant was tissue-specific; e) pronase treatment abolished binding capacity for (3H)T; f) bound radioactivity consisted solely of (3H)T; and g) the mesonephric and ductal segment of the genital tract specifically binds (3H)T. The data demonstrate binding protein(s), specific for testosterone and possibly dihydrotestosterone, in the genital ducts of 14.5-15-day-old fetal rats. (3H)T binding to genital duct supernatants from male but not from female fetuses increased about 5-fold between 14.5 and 20.5 days of gestation. Upon Sephadex G-100 gel filtration, radioactivity was confined to the macromolecular fraction appearing in the void volume. Nuclear fractions, obtained from intact ducts incubated with (3H)T at 30 C but not at 0 C contained radioactivity. These observations are compatible with the existence of a cytoplasmic testosterone receptor or carrier protein aggregate. We have thus concluded that testosterone-binding proteins are present in the genital ducts of rat fetuses and that, in the male, their concentrations increase with progressive Wolffian duct differentiation.

Animals↗

PubMed1976

The identification of myosin in rabbit hepatocytes.

A myosin-like protein was identified in isolated rabbit liver cells. It was extracted with high-ionic-strength buffer containing ATP, and purified by gel filtration in the presence of iodide. The myosin polypeptide was indistinguishable in size from the heavy chain of muscle myosin as determined by electrophoresis on polyacrylamide gels and gel filtration in the presence of sodium dodecyl sulfate. The hepatic myosin had an amino acid composition similar to that of muscle myosin, but lacked 3-methylhistidine. The Mg2+ -ATPase of the myosin was not activated by muscle actin. At low ionic strength, in the presence of Mg2+, the protein aggregated to form bipolar filaments 0.3 mum in length. A protein which resembled muscle actin in size and amino acid composition was extracted along with the myosin. Based on scans of stained sodium dodecyl sulfate polyacrylamide gels, the myosin content was estimated as 0.3% to 0.4% of the cell protein. The actin-like component was present in approximately ten-fold excess by weight. This ratio suggests that the organization and function of myosin in the hepatocyte is very different from that in the muscle cell.

Adenosine Triphosphatases↗

PubMed1975

Thermal transitions of myosin and its helical fragments. I. Shifts in proton equilibria accompanying unfolding.

The thermal transitions of myosin and its helical fragments have been studied with pH as the observable. Heating unbuffered solutions of these proteins near their pI values causes an abrupt rise in pH at a characteristic temperature (the "melting temperature," Tm) which is due to structural changes within the protein. Since the pH shift turns out to be insensitive to the degree of protein aggregation, we have obtained acceptable melting curves even under conditions where the protein coagulates during melting. The melting profiles and Tm vlaues of myosin, myosin rod, and light meromyosin have been found to be remarkably similar (Tm equal to 40 plus or minus 1 degree, 0.5 M KCl, pH 5.9). Proton binding which occurs during melting coincides with the unfolding of a section of myosin rod. Taken in the context of other studies, the proton binding is thought to occur near the "hinge region."

Animals↗

PubMed1978

Proposed knobs-into-holes packing for several membrane proteins.

We investigated the possible side chain/side chain interactions of four potential transmembrane proteins. The basic assumptions are that the proteins are alpha-helical, and that the proteins aggregate with knobs-into-holes packing. It was found that these four proteins can be assembled into stereochemically feasible bundles of alpha-helices with hydrophobic exteriors and with hydrogen bonds between the side chains of one alpha-helix and the side chains of its knobs-into-holes packed neighbors.

Bacteriophages↗

PubMed1978

Formation of protein micelles from amphiphilic membrane proteins.

The membrane penicillinase (penicillin amido-beta-lactamhydrolase, EC 3.5.2.6) from Bacillus licheniformis, the Semliki Forest virus spike proteins, and the Sendai virus glycoproteins have each been isolated as soluble protein aggregates that are virtually free of lipid and detergent. The sedimentation coefficients of the complexes were 18 S, 29 S, and 43 S, respectively. Mixed aggregates containing both the virus glycoproteins and the penicillinase could also be formed. Such protein micelles may serve a number of useful purposes in membrane research.

Antibodies↗

PubMed2024

Molecular Signatures of Neurodegenerative Diseases Identified by Proteomic and Phosphoproteomic Analyses in Aging Mouse Brain.

A central hallmark of neurodegenerative diseases is the irreversible accumulation of misfolded proteins in the brain by aberrant phosphorylation. Understanding the mechanisms underlying protein phosphorylation and its role in pathological protein aggregation within the context of aging is crucial for developing therapeutic strategies aimed at preventing or reversing such diseases. Here, we applied multi-protease digestion and quantitative mass spectrometry to compare and characterize dysregulated proteins and phosphosites in the mouse brain proteome using three different age groups: young-adult (3-4 months), middle-age (10 months), and old mice (19-21 months). Proteins associated with senescence, neurodegeneration, inflammation, cell cycle regulation, the p53 hallmark pathway, and cytokine signaling showed significant age-dependent changes in abundances and level of phosphorylation. Several proteins implicated in Alzheimer's disease (AD) and Parkinson's disease (PD) including tau (Mapt), Nefh, and Dpysl2 (also known as Crmp2) were hyperphosphorylated in old mice brain suggesting their susceptibility to the diseases. Cdk5 and Gsk3b, which are known to phosphorylate Dpysl2 at multiple specific sites, had also increased phosphorylation levels in old mice suggesting a potential crosstalk between them to contribute to AD. Hapln2, which promotes α-synuclein aggregation in patients with PD, was one of the proteins with highest abundance in old mice. CD9, which regulates senescence through the PI3K-AKT-mTOR-p53 signaling was upregulated in old mice and its regulation was correlated with the activation of phosphorylated AKT1. Overall, the findings identify a significant association between aging and the dysregulation of proteins involved in various pathways linked to neurodegenerative diseases with potential therapeutic implications.

Animals↗

PubMed1977

[The anaphylactoid reaction after colloid infusion].

All colloidal volume substitutes carry the risk of anaphylactoid reactions. The general incidence of 0.03% is low; however severe complications can occur. There are differnet pathomechanisms involved in the induction of anaphylactoid reactions after infusion of different colloids. Protein aggregates are of pathogenic importance in human serum albumin incompatibility. The addition of stabilizers to the plasma protein solutions can alter the immunogenicity of the protein molecule. Antibodies of the classes IgG and IgM seem to play a role in severe dextran incompatibility. There was a direct correlation of the intensity of the clinical symptoms with the anti-dextran-antibody titer.

Anaphylaxis↗

PubMed1978

An electron microscope study of the proteins attached to polio virus RNA and its replicative form (RF).

A recently described method (Wu, M. and Davidson, N. (1978), Nucleic Acids Research 5, in press) for visualizing proteins attached to nucleic acids in the electron microscope has been applied to study proteins attached to poliovirion RNA and to the viral double-stranded intracellular RF form. A protein is found at the 5' end of the plus strand virion RNA, and protein components are found at both ends of the duplex RF. In the RF as usually extracted, there is frequently a larger or compound protein aggregate at the end which contains the 3' end of the plus strand and the 5' end of the minus strand. Banding in CsCl-guanidinium hydrochloride in the presence of sarkosyl causes dissociation of some components of this aggregate, leaving both ends labeled with the covalently bound VPg. These results confirm and extend previous biochemical studies of proteins bound to poliovirion RNA and to the RF form.

Cytochrome c Group↗

PubMed1976

Protein components in the very low density lipoproteins of hen's egg yolks. Identification of highly aggregating (gelling) and less aggregating (non-gelling) proteins.

Apoproteins of hen's egg yolk very low density lipoprotein has been separated by Sephadex G-200 gel filtration in 0.5% sodium dodecyl sulfate into three categories of proteins termed apoprotein A, apoprotein B and apoprotein C. Apoprotein A fraction consists of several aggregated proteins (linked possibly by -S-S- bridges) as shown by acrylamide gel electrophoresis in the presence of 2-mercaptoethanol. Apoprotein B contains two major protein components, B1 and B2, with molecular weights of 78 000 and 64 000, respectively, and two minor proteins components. Apoprotein C was obtained in a pure form as a low molecular weight, -S-S- linked dimer protein and accounted for about 30% of the total protein. In the monomeric form, apoprotein C has a molecular weight of 9400. Apoprotein A and apoprotein B have similar amino acid composition, except in isoleucine content which is over two times in apoprotein B as compared to apoprotein A. Apoprotein C lacks histidine and is richer in arginine than apoproteins A or B. Apoprotein C has lysine as N-terminal, while apoproteins A and B have predominantly arginine as the N-terminal amino acid. All the three fractions contain carbohydrate residues, apoprotein B being the richest in carbohydrate content. Cold-stored apoproteins A forms a clear gel when dispersed in 0.5% sodium dodecyl sulfate at concentration of above 2 mg/ml, while apoprotein B forms a gel only above 10 mg/ml. Apoprotein C, even at 35 mg/ml, forms a clear solution with no tendency to gel.

Amino Acid Sequence↗

PubMed1976

Release and activation of a particulate bound acid phosphatase from Tetrahymena pyriformis.

A sedimentable form of acid phosphatase (EC 3.1.3.2) from Tetrahymena pyriformis was found to be solubilized by Triton X-100. The total enzyme activity in the insoluble cell fraction increased almost 200% upon solubilization with Triton X-100 or Nonidet P-40. Removal of membrane lipids and Triton X-100 from the particulate wash solution with a chloroform extraction resulted in non-specific enzyme-protein aggregation which was reversible upon addition of Triton X-100. The results indicate that this acid phosphatase is an integral membrane protein. The pH optima for this particulate bound acid phosphatase was 3.5 with o-carboxyphenyl phosphate and 4.0 with p-nitrophenyl phosphate as substrates. The Km values of each substrate were 3.1 and 0.031 mM, respectively.

Acid Phosphatase↗