Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Protein aggregation”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 145 records · Page 8Linked to original sources
PubMed2004

Thermotolerance requires refolding of aggregated proteins by substrate translocation through the central pore of ClpB.

Cell survival under severe thermal stress requires the activity of the ClpB (Hsp104) AAA+ chaperone that solubilizes and reactivates aggregated proteins in concert with the DnaK (Hsp70) chaperone system. How protein disaggregation is achieved and whether survival is solely dependent on ClpB-mediated elimination of aggregates or also on reactivation of aggregated proteins has been unclear. We engineered a ClpB variant, BAP, which associates with the ClpP peptidase and thereby is converted into a degrading disaggregase. BAP translocates substrates through its central pore directly into ClpP for degradation. ClpB-dependent translocation is demonstrated to be an integral part of the disaggregation mechanism. Protein disaggregation by the BAP/ClpP complex remains dependent on DnaK, defining a role for DnaK at early stages of the disaggregation reaction. The activity switch of BAP to a degrading disaggregase does not support thermotolerance development, demonstrating that cell survival during severe thermal stress requires reactivation of aggregated proteins.

Cell Survival↗
PubMed2003

The effects of arginine on refolding of aggregated proteins: not facilitate refolding, but suppress aggregation.

Arginine is one of the universal reagents that are effective in assisting refolding of recombinant proteins from inclusion bodies. The mechanism of the effects of arginine on refolding has remained, however, to be elucidated. Here we show that arginine does not stabilize proteins against heat treatment, as demonstrated by little change in melting temperature. It does increase reversibility of thermal melting and reduce aggregation under thermal stress. The observations suggest that arginine may not facilitate refolding, but may suppress aggregation of the proteins during refolding.

Animals↗
PubMed1999

Molecular pathogenesis of movement disorders: are protein aggregates a common link in neuronal degeneration?

Abnormal protein aggregation has been postulated to explain the molecular basis for many neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease and prion diseases, as well as trinucleotide repeat disorders. The recent findings that mutations in alpha-synuclein lead to autosomal-dominant, early-onset Parkinson's disease in some families and that alpha-synuclein is found in Lewy bodies of all Parkinson's disease patients prompted the hypothesis that the pathophysiology of all Parkinson's disease patients starts with an abnormal folding of alpha-synuclein, producing excessive aggregation that overwhelms the antiaggregation mechanisms of the cell. The genetics of Parkinson's disease and polyglutamine repeat disorders and the evidence of abnormal processing and aggregation of the respective target proteins for the aetiology and pathogenesis in these diseases are reviewed.

Cell Aggregation↗
PubMed2006

A critical review of analytical ultracentrifugation and field flow fractionation methods for measuring protein aggregation.

Analytical ultracentrifugation (AUC) and field flow fractionation (FFF) are 2 important biophysical methods for measuring protein aggregates. Both methods can separate protein monomer from its aggregate forms under a broad range of solution conditions. Recent advances in instrumentation and data analysis, particularly in the field of analytical ultracentrifugation technology, have significantly improved the capability and sensitivity of these biophysical methods for detecting protein aggregates. These advances have resulted in an increased use of these methods in the biopharmaceutical industry for characterization of therapeutic proteins. However, despite their many advantages over conventional methods, the difficulty in the use of the instrumentation and the complexity of data analysis process, have often hampered the widespread use and proper interpretation of data. This article reviews the recent progress in both technologies, and a few case studies are also presented to discuss their advantages and limitations.

Biological Products↗
PubMedDate not supplied

In vitro release profiles of eristostatin from biodegradable polymeric microspheres: protein aggregation problem.

Eristostatin, a low molecular weight polypeptide (MW 5725), was encapsulated within two biodegradable poly(lactic acid-glycolic acid) microspheres. In vitro release profiles from the microspheres exhibited fast initial release for up to several days, followed by very slow or no release. The later stage of the slow release was due to protein aggregation within the microspheres. A simple, noninvasive method to detect the protein aggregation within the microspheres has been developed: extraction of radiolabeled protein from the microspheres by a DC electric field into a polyacrylamide gel and subsequent exposure to a gamma-ray sensitive film. Direct application of the degrading microspheres onto the sample loading zone of sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) could successfully extract the monomeric and oligomeric proteins into the autoradiogram of a gel slab, while unextractable protein aggregates within the microspheres could be directly visualized in their loading position.

Autoradiography↗
PubMed1997

Natural and artificial carbohydrate-glued protein aggregates.

Carbohydrate gluing (which may have a carbohydrate-lectin binding mechanism) was first recognized as a major contributor in the supramolecular assembly of annelid giant Hb from the marine-worm P. aibuhitensis. Although this assembly obviously also relies on protein-protein interactions, the authors tested the application of carbohydrate gluing in the assembly of a protein aggregate using a lectin and a carbohydrate-containing protein. The resultant aggregate was a mixture of the protein aggregate and the ingredient proteins. The significance of the method is that the assembly of the aggregate can be controlled by using a hapten sugar. This controllability, in conjunction with newly developing glyco-technology, has great potential for the construction of arbitrary protein molecules into a regular protein aggregate, thereby providing sophisticated functions.

Animals↗
PubMed2002

Induction of cyclooxygenase-2 expression in glomeruli by aggregated protein.

Cyclooxygenase has two isozymes, a constitutive type (cyclooxygenase-1) and an inducible type (cyclooxygenase-2). The aim of the present study was to determine whether cyclooxygenase-2 is associated with the increased production in prostaglandin E2 in glomeruli by aggregated protein. Mice were injected with aggregated bovine serum albumin. Glomeruli were isolated using sieves and a magnet. Production of prostaglandin E2 was increased in glomeruli after injection of aggregated bovine serum albumin. RT-PCR analysis indicated enhanced expression of cyclooxygenase-2 mRNA in aggregated bovine serum albumin-loaded glomeruli. Western blotting analysis indicated an increase in cyclooxygenase-2 protein in glomeruli by aggregated bovine serum albumin. Glomeruli were incubated with indomethacin, NS-398 or niflumic acid in the presence of arachidonic acid. Indomethacin resulted in remarkable reduction of prostaglandin E2 levels in aggregated bovine serum albumin-loaded glomeruli. Niflumic acid also inhibited prostaglandin E2 production, and its inhibitory rate was more than that of NS-398. In conclusion, aggregated protein induces cyclooxygenase-2 in glomeruli, suggesting that cyclooxygenase-2 is involved in the process of disposal of aggregated protein in glomeuli.

Animals↗
PubMedDate not supplied

Protein aggregation and pathogenesis of Huntington's disease: mechanisms and correlations.

The formation of insoluble protein aggregates is a hallmark of Huntington's disease (HD) and related neurodegenerative disorders, such as dentatorubral pallidoluysian atrophy (DRPLA), spinal bulbar muscular atrophy (SBMA) and the spinocerebellar ataxia (SCA) type 1, 2, 3, 6 and 7. These disorders are caused by an expanded polyglutamine (polyQ) tract in otherwise unrelated proteins. They are characterized by late-onset, selective neuropathology, a pathogenic polyQ threshold and a relationship between polyQ length and disease progression. Thus, molecular models of HD and related glutamine-repeat disorders must account for these characteristic features. During the last three years, considerable effort has been invested in the development of in vitro and in vivo model systems to study the mechanisms of protein aggregation in glutamine-repeat disorders and its potential effects on disease progression and neurodegeneration. A selection of these studies is reviewed here. Furthermore, the correlation between aggregate formation and development of HD is discussed.

Animals↗
PubMed1992

Monitoring in vivo lens changes. A comparative study with biochemical analysis of protein aggregation.

In this study the AA attempted to evaluate the relationship between lens optical density and lens fluorescence determined in vivo, with some specific (in vitro) biochemical changes occurring during cataract development. Special attention has been given to the comparison between diabetic and non diabetic cataracts. Prior to surgery all lenses were analysed by Scheimpflug photography to evaluate the topography of opacities and fluorescence distribution. Individual lenses were separated into cortex and nucleus and the amount of high molecular weight (HMW) protein aggregates was determined by FPLC (Fast Performance Liquid Chromatography). The results found in this study have shown that, as it would be expected, diabetic cataractous lenses present higher fluorescence levels than senile cataracts. It has also been shown that the increase in lens optical density, determined by Scheimpflug photography is clearly related to the increase in the amount of HMW-aggregates. Furthermore, in diabetic cataracts, a good correlation between protein aggregation and lens fluorescence determined in vivo has been found. Thus, it seems that in diabetic cataracts chemical or metabolic mechanisms leading to the production of fluorescent chromophores may be related to protein aggregation and therefore to the major processes involved in cataract development.

Aged↗
PubMed1995

Cooperation of the molecular chaperone Ydj1 with specific Hsp70 homologs to suppress protein aggregation.

Ydj1p, a cytosolic DnaJ homolog from Saccharomyces cerevisiae, is demonstrated to function as a molecular chaperone. Purified Ydj1p formed complexes with non-native polypeptides and suppressed protein aggregation. Ydj1p cooperated with Ssa Hsp70 proteins in the prevention of protein aggregation, but not with the Ssb Hsp70 proteins. Cooperation between these different molecular chaperones was only observed in the presence of hydrolyzable ATP and correlated with the ability of Ydj1p to stimulate the ATPase activity of the Hsp70 homolog with which it was paired. The regulatory and chaperone activities of a eukarytic DnaJ homolog thus act together to assist Hsp70 in modulating the conformation of proteins.

Adenosine Triphosphate↗
PubMed2006

Simulations as analytical tools to understand protein aggregation and predict amyloid conformation.

Computational tools are increasingly being applied to solve the protein aggregation problem, providing insight into amyloid structures and aggregation mechanisms. The paradigm of Abeta amyloid structure elucidation provides an example of an innovative experimental design and endeavor, echoing the computational testing of possible molecular associations, all reflected in the current Ma-Nussinov-Tycko model of the Abeta amyloid. Simulations have shown that dimer formation can lock some misfolded conformations, and catalyze the shift of the equilibrium away from the native state. In most cases, a stable amyloid seed requires at least two-layered beta-sheets with properly registered side-chains. Under kinetic control, the final protein aggregations are the outcome of maximizing the van der Waals interactions between side chains and backbone hydrogen bonds.

Amyloid↗
PubMed2006

Protein aggregation and its consequences for human disease.

Protein molecules have emerged through evolution so that they are able to remain in their functional and soluble states under normal physiological conditions, although in other situations they often have a high propensity to aggregate. Aggregation in vivo is associated with a wide range of human disorders, including Alzheimer's disease and type II diabetes, medical conditions that are becoming increasingly common in the modern world. In such diseases, aggregated proteins can often be observed as highly intractable thread-like species known as amyloid fibrils. This article provides an overview of our present knowledge of the nature of these fibrillar aggregates and the manner in which they form, and discusses the origins and potential means of suppression of the pathogenic properties with which they and their precursors are associated.

Alzheimer Disease↗
PubMed2004

Kinetics of protein aggregation with formation of unreactive intermediates.

Irreversible protein aggregation resulting in formation and deposition of insoluble fibrils or amorphous precipitates is usually assumed to occur via sequential attachment of monomers to soluble intermediates. We complement this scheme by slow conversion of the intermediates to a relatively stable form so that they do not react with monomers but can be trapped by precipitates. For reasonable values of parameters, our model predicts that the aggregation kinetics order may be between 2.0 and 2.5. In particular, the model can be used to explain the reaction order, 2.17 +/- 0.09, observed for aggregation of recombinant human granulocyte colony stimulating factor.

Kinetics↗
PubMed2005

Disulphide bond formation in food protein aggregation and gelation.

In this short review we discuss the role of cysteine residues and cystine bridges for the functional aggregation of food proteins. We evaluate how formation and cleavage of disulphide bonds proceeds at a molecular level, and how inter- and intramolecular disulfide bonds can be detected and modified. The differences between heat-, high-pressure-, and denaturant-induced unfolding and aggregation are discussed. The effect of disulphide bonding between aggregates of proteins and protein mixtures on the functional macroscopic properties of space filling networks in protein gels is briefly presented.

Disulfides↗
PubMed2004

Effects of platelet inhibitors on propyl gallate-induced platelet aggregation, protein tyrosine phosphorylation, and platelet factor 3 activation.

Propyl gallate (PG) is a platelet agonist characterized by inducing platelet aggregation, protein tyrosine phosphorylation, and platelet factor 3 activity. The mechanisms of platelet activation following PG stimulation were examined by pre-incubating platelets with well-defined platelet inhibitors using platelet aggregation, protein tyrosine phosphorylation, activated plasma clotting time, and annexin V binding by flow cytometry. PG-induced platelet aggregation and tyrosine phosphorylation of multiple proteins were substantially abolished by aspirin, apyrase, and abciximab (c7E3), suggesting that PG is associated with activation of platelet cyclooxygenase 1, adenosine phosphate receptors, and glycoprotein IIb/IIIa, respectively. The phosphorylation of the cytoskeletal enzyme pp60(c-src) increased following PG stimulation, but was blunted by pre-incubation of platelets with aspirin, apyrase, and c7E3, suggesting that tyrosine kinase is important for the signal transduction of platelet aggregation. Propyl gallate also activates platelet factor 3 by decreasing the platelet coagulation time and increasing platelet annexin V binding. Platelet incubation with aspirin, apyrase, and c7E3 did not alter PG-induced platelet coagulation and annexin V binding. The results suggest that platelet factor 3 activation and membrane phosphotidylserine expression were not involved with activation of platelet cyclooxygenase, adenosine phosphate receptors, and glycoprotein IIb/IIIa. PG is unique in its ability to stimulate platelet aggregation and coagulation simultaneously, and platelet inhibitors in this study affect only platelet aggregation but not platelet coagulation.

Annexin A5↗
PubMed1985

Ultrasonic absorption in tobacco mosaic virus and its protein aggregates.

The structural fluctuations specific to self-assembled biological systems have been investigated further with ultrasonic techniques by using two strains of tobacco mosaic virus (TMV), as well as the helical aggregate of the common strain protein and subassemblies of it. We confirmed our earlier conclusion that protein assemblies exhibit specific structural fluctuations detected in ultrasonic experiments. As in spherical viruses, the fluctuations exhibited by the protein aggregates having a quaternary structure similar to that of the virion were modified in the virus by interaction with the RNA strand. It is unlikely that the origin for the observed effect is due either to: (1) the difference in local mobility of the segment 89 to 113 of the polypeptide chain in TMV and in the helical aggregate on the one hand, and in smaller aggregates, on the other hand; or (2) a local fluctuation associated with proton transfer reactions or ion-pair interactions. The most remarkable feature in the TMV system is the fact that the two-ring disk showed no excess of ultrasonic absorption with respect to the A-protein oligomer, while a large increase of ultrasonic absorption was observed in the rod-like aggregate that had undergone the disk-helix transition.

Hydrogen-Ion Concentration↗
PubMed1996

Secretory granule content proteins and the luminal domains of granule membrane proteins aggregate in vitro at mildly acidic pH.

A major unresolved issue in the field of secretory granule biogenesis is the extent to which the aggregation of granule content proteins is responsible for the sorting of regulated from constitutively secreted proteins. The aggregation process is postulated to take place in the trans-Golgi network and immature secretory granules as the proteins encounter mildly acidic pH and high calcium concentrations. We have developed in vitro assays that reconstitute the precipitation out of solution of secretory granule content proteins of anterior pituitary gland and adrenal medulla. In the assays, all of the major granule content polypeptides form a precipitate as the pH is titrated below 6.5, and this precipitate can be recovered in the pellet fraction after centrifugation. Addition of calcium is required for the aggregation of chromaffin granule content. In contrast to the proteins secreted by the regulated pathway, the constitutively secreted proteins IgG, albumin, and angiotensinogen, when added to the assays, remain predominantly in the supernatant. Among the individual proteins tested, prolactin is found to aggregate homophilically under these conditions and can drive the co-aggregation of other proteins, such as the chromogranins. Soluble forms of granule membrane proteins, including dopamine beta-hydroxylase and peptidyl glycine alpha-amidating enzyme also co-aggregated with granule content proteins. The results are consistent with the idea that spontaneous aggregation of proteins occurring under ionic conditions similar to those at the sites of granule formation is a property restricted to those proteins packaged in secretory granules. In addition, the association of luminal domains of membrane proteins with content proteins in vitro raises the possibility that analogous interactions between membrane-bound and content proteins also occur during granule formation in intact cells.

Animals↗
PubMed2003

Trimethoprim induces heat shock proteins and protein aggregation in E. coli cells.

Trimethoprim (TMP), an inhibitor of dihydrofolate reductase, decreases the level of tetrahydrofolate supplying one-carbon units for biosynthesis of nucleotides, proteins, and panthotenate. We have demonstrated for the first time that one of the effects of the TMP action in E. coli cells is protein aggregation and induction of heat shock proteins (Hsps). TMP caused induction of DnaK, DnaJ, GroEL, ClpB, and IbpA/B Hsps. Among these Hsps, IbpA/B were most efficiently induced by TMP and coaggregated with the insoluble proteins. Upon folate stress, deletion of the delta ibpA/B operon resulted in increased protein aggregation but did not influence cell viability.

Escherichia coli↗