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At least 415 records · Page 23Linked to original sources
PubMed2006

The structural biology of protein aggregation diseases: Fundamental questions and some answers.

Amyloid fibrils are found in association with at least two dozen fatal diseases. The tendency of numerous proteins to convert into amyloid-like fibrils poses fundamental questions for structural biology and for protein science in general. Among these are the following: What is the structure of the cross-beta spine, common to amyloid-like fibrils? Is there a sequence signature for proteins that form amyloid-like fibrils? What is the nature of the structural conversion from native to amyloid states, and do fibril-forming proteins have two distinct stable states, the native state and the amyloid state? What is the basis of protein complementarity, in which a protein chain can bind to itself? We offer tentative answers here, based on our own recent structural studies.

Amyloid↗
PubMed1978

Quantitative verification of the existence of high molecular weight protein aggregates in the intact normal human lens by light-scattering spectroscopy.

The method of quasi-elastic light-scattering spectroscopy was used to establish quantitatively the concentration of high mmolecular weight (HMW) aggregates present in the normal human intact lens as a function of age. The concentration of HMW proteins increases monotonically with age. HMW proteins are absent in the infant lens, but represent 3% of the total soluble lens protein at age 60 years. The percent concentration of HMW proteins measured in intact lenses of various ages by quasi-elastic light scattering is in striking agreement with values determined biochemically.

Adolescent↗
PubMed2005

Coincident thresholds of mutant protein for paralytic disease and protein aggregation caused by restrictively expressed superoxide dismutase cDNA.

Familial amyotrophic lateral sclerosis (FALS) has been modeled in transgenic mice by introducing mutated versions of human genomic DNA encompassing the entire gene for Cu,Zn superoxide dismutase (SOD1). In this setting, the transgene is expressed throughout the body and results in mice that faithfully recapitulate many pathological and behavioral aspects of FALS. By contrast, transgenic mice made by introducing recombinant vectors, encoding cDNA genes, that target mutant SOD1 expression to motor neurons, only, or astrocytes, only, do not develop disease. Here, we report that mice transgenic for human SOD1 cDNA with the G37R mutation, driven by the mouse prion promoter, develop motor neuron disease. In this model, expression of the transgene is highest in CNS (both neurons and astrocytes) and muscle. The gene was not expressed in cells of the macrophage lineage. Although the highest expressing hemizygous transgenic mice fail to develop disease by 20 months of age, mice homozygous for the transgene show typical ALS-like phenotypes as early as 7 months of age. Spinal cords and brain stems from homozygous animals with motor neuron disease were found to contain aggregated species of mutant SOD1. The establishment of this SOD1-G37R cDNA transgenic model indicates that expression of mutant SOD1 proteins in the neuromuscular unit is sufficient to cause motor neuron disease. The expression levels required to induce disease coincide with the levels required to induce the formation of SOD1 aggregates.

Amyotrophic Lateral Sclerosis↗
PubMed1997

The Hsp70 homologue Lhs1p is involved in a novel function of the yeast endoplasmic reticulum, refolding and stabilization of heat-denatured protein aggregates.

Heat stress is an obvious hazard, and mechanisms to recover from thermal damage, largely unknown as of yet, have evolved in all organisms. We have recently shown that a marker protein in the ER of Saccharomyces cerevisiae, denatured by exposure of cells to 50 degrees C after preconditioning at 37 degrees C, was reactivated by an ATP-dependent machinery, when the cells were returned to physiological temperature 24 degrees C. Here we show that refolding of the marker enzyme Hsp150Delta-beta-lactamase, inactivated and aggregated by the 50 degrees C treatment, required a novel ER-located homologue of the Hsp70 family, Lhs1p. In the absence of Lhs1p, Hsp150Delta-beta-lactamase failed to be solubilized and reactivated and was slowly degraded. Coimmunoprecipitation experiments suggested that Lhs1p was somehow associated with heat-denatured Hsp150Delta- beta-lactamase, whereas no association with native marker protein molecules could be detected. Similar findings were obtained for a natural glycoprotein of S. cerevisiae, pro-carboxypeptidase Y (pro-CPY). Lhs1p had no significant role in folding or secretion of newly synthesized Hsp150Delta-beta-lactamase or pro-CPY, suggesting that the machinery repairing heat-damaged proteins may have specific features as compared to chaperones assisting de novo folding. After preconditioning and 50 degrees C treatment, cells lacking Lhs1p remained capable of protein synthesis and secretion for several hours at 24 degrees C, but only 10% were able to form colonies, as compared to wild-type cells. We suggest that Lhs1p is involved in a novel function operating in the yeast ER, refolding and stabilization against proteolysis of heatdenatured protein. Lhs1p may be part of a fundamental heat-resistant survival machinery needed for recovery of yeast cells from severe heat stress.

Endoplasmic Reticulum↗
PubMed2006

Stoichiometric inhibition of amyloid beta-protein aggregation with peptides containing alternating alpha,alpha-disubstituted amino acids.

We have prepared two peptides based on the hydrophobic core (Lys-Leu-Val-Phe-Phe) of amyloid beta-protein (Abeta) that contain alpha,alpha-disubstituted amino acids at alternating positions, but differ in the positioning of the oligolysine chain (AMY-1, C-terminus; AMY-2, N-terminus). We have studied the effects of AMY-1 and AMY-2 on the aggregation of Abeta and find that, at stoichiometric concentrations, both peptides completely stop Abeta fibril growth. Equimolar mixtures of AMY-1 and Abeta form only globular aggregates as imaged by scanning force microscopy and transmission electron microscopy. These samples show no signs of protofibrillar or fibrillar material even after prolonged periods of time (4.5 months). Also, 10 mol % of AMY-1 prevents Abeta self-assembly for long periods of time; aged samples (4.5 months) show only a few protofibrillar or fibrillar aggregates. Circular dichroism spectroscopy of equimolar mixtures of AMY-1 and Abeta show that the secondary structure of the mixture changes over time and progresses to a predominantly beta-sheet structure, which is consistent with the design of these inhibitors preferring a sheet-like conformation. Changing the position of the charged tail on the peptide, AMY-2 interacts with Abeta differently in that equimolar mixtures form large ( approximately 1 mum) globular aggregates which do not progress to fibrils, but precipitate out of solution. The differences in the aggregation mediated by the two peptides is discussed in terms of a model where the inhibitors act as cosurfactants that interfere with the native ability of Abeta to self-assemble by disrupting hydrophobic interactions either at the C-terminus or N-terminus of Abeta.

Amino Acids↗
PubMed2006

Size frequency distributions of the florid prion protein aggregates in variant Creutzfeldt-Jakob disease follow a power-law function.

The objective was to test the hypothesis that the size frequency distributions of the prion protein (PrP) plaques in cases of variant Creutzfeldt-Jakob disease (vCJD) follow a power-law function. The design was a retrospective neuropathological study. The patients were 11 cases of clinically and neuropathologically verified vCJD. Size distributions of the diffuse and florid-type plaques were measured in several areas of the cerebral cortex and hippocampus from each case and a power-law function fitted to each distribution. The size distributions of the florid and diffuse plaques were fitted successfully by a powerlaw function in 100% and 42% of brain areas investigated respectively. Processes of aggregation/disaggregation may be more important than surface diffusion in the pathogenesis of the florid plaques. By contrast, surface diffusion may be a more significant factor in the development of the diffuse plaques.

Adolescent↗
PubMed2004

Protein aggregation during overexpression limited by peptide extensions with large net negative charge.

Folding of the human coxsackie and adenovirus receptor immunoglobulin (Ig) variable-type domain (CAR D1) during overexpression in the Escherichia coli cytoplasm was shown previously to be partially rescued by fusion to a 22-residue C-terminal peptide. Here, peptide sequence features required for solubilization and folding of CAR D1 and similar Ig variable-type domains from two other human membrane proteins were investigated. Peptide extensions with net negative charge > -6 fully solubilized CAR D1, and approximately half of the peptide-solubilized protein was correctly folded. The Ig variable-type domains from human A33 antigen and myelin P-zero proteins were only partially solubilized by peptide extensions with net charge of -12, however, and only the solubilized P-zero domain appeared to fold correctly whereas the A33 domain formed soluble microaggregates of misfolded protein. Our results suggest a model where the large net charge of peptide extensions increases electrostatic repulsion between nascent polypeptides. The resulting decrease in aggregation rate can enable some polypeptides to fold spontaneously into their native protein conformations. Analysis of the solubility and folding status of sets of structurally homologous proteins, such as the Ig variable-type domains described here, during overexpression could provide insights into how amino acid and gene sequences influence the efficiency of spontaneous protein folding.

Amino Acids↗
PubMed1995

The effects of aggregation, protein binding and cellular incorporation on the photophysical properties of benzoporphyrin derivative monoacid ring A (BPDMA).

Absorption, fluorescence and laser flash photolysis spectroscopies were used to investigate the effects of self-aggregation, binding to human serum albumin and incorporation in cancer cells on the photophysics of benzoporphyrin derivative monoacid ring A (BPDMA). Aggregation of BPDMA has been studied in mixtures of methanol and phosphate-buffered saline (PBS). The extent of aggregation was dependent on dye concentration and solvent composition, becoming particularly marked in mixtures containing less than 30% methanol. A dimerization constant Kd or 9 x 10(6) M-1 was determined by fluorescence experiments for BPDMA in pure PBS. In addition to spectral modifications, aggregation induces a lowering of the fluorescence and intersystem crossing quantum yields. Human serum albumin binds BPDMA with an association constant Kb of 5.2 x 10(5) M-1 in PBS. When bound to HSA, BPDMA displays photophysical properties very similar to the monomer in organic solvents. The molar ratio [HSA]/[BPDMA] corresponding to complete binding of the dye was determined to be approximately 10. Efficient generation of the triplet state of BPDMA was also observed from aqueous cellular suspensions containing incorporated photosensitizer.

Animals↗
PubMedDate not supplied

Bicarbonate-dependent lipid ordering and protein aggregation are part of the nongenomic action of progesterone on capacitated spermatozoa.

The nongenomic action of progesterone (P) on capacitated sperm in mediating acrosomal exocytosis operates through transmembrane signal transduction involving increased intracellular calcium ions and modulation of protein kinases and phospholipid metabolism through a second messenger pathway. Conflicting views exist regarding the nature of the nongenomic receptor of P. It is thought to be a cell-surface receptor having the properties of a calcium channel, chloride channel, bicarbonate/chloride exchanger, and gamma aminobutyric acid type A (GABA(A)). In this study, we tried to understand the role of bicarbonate and/or P in inducing membrane perturbations in capacitated and acrosome-reacting spermatozoa. We also attempted to characterize the membrane responses in P-stimulated and bicuculline-poisoned sperm. The presence of a high level of bicarbonate in the medium favored high rotational mobility of lipids and proteins in capacitated sperm. However, the capacitated sperm exhibited low lipid ordering and unaltered protein ordering in response to the high bicarbonate concentration. P and bicuculline appeared to bind to the same or similar binding sites, probably a GABA(A) receptor, eliciting similar motional perturbations in sperm membranes. It appears that both P and bicuculline can induce receptor aggregation and lipid ordering in sperm membranes, which alter the capability of sperm to bind zona pellucida, and that the P action on sperm takes effect through a bicarbonate-dependent signal transduction mechanism.

Acrosome Reaction↗