81 research outputs found
The quaternary organization and dynamics of the molecular chaperone HSP26 are thermally regulated
No full textThe function of ScHSP26 is thermally controlled: the heat shock that causes the destabilization of target proteins leads to its activation as a molecular chaperone. We investigate the structural and dynamical properties of ScHSP26 oligomers through a combination of multiangle light scattering, fluorescence spectroscopy, NMR spectroscopy, and mass spectrometry. We show that ScHSP26 exists as a heterogeneous oligomeric ensemble at room temperature. At heat-shock temperatures, two shifts in equilibria are observed: toward dissociation and to larger oligomers. We examine the quaternary dynamics of these oligomers by investigating the rate of exchange of subunits between them and find that this not only increases with temperature but proceeds via two separate processes. This is consistent with a conformational change of the oligomers at elevated temperatures which regulates the disassembly rates of this thermally activated protein.Justin L.P. Benesch, J. Andrew Aquilina, Andrew J. Baldwin, Agata Rekas, Florian Stengel, Robyn A. Lindner, Eman Basha, Glyn L. Devlin, Joseph Horwitz, Elizabeth Vierling, John A. Carver, and Carol V. Robinsonhttp://www.cell.com/chemistry-biology/hom
The interaction of alphaB-crystallin with mature alpha-synuclein amyloid fibrils inhibits their elongation
No full textαB-Crystallin is a small heat-shock protein (sHsp) that is colocalized with α-synuclein (αSyn) in Lewy bodies—the pathological hallmarks of Parkinson's disease—and is an inhibitor of αSyn amyloid fibril formation in an ATP-independent manner in vitro. We have investigated the mechanism underlying the inhibitory action of sHsps, and here we establish, by means of a variety of biophysical techniques including immunogold labeling and nuclear magnetic resonance spectroscopy, that αB-crystallin interacts with αSyn, binding along the length of mature amyloid fibrils. By measurement of seeded fibril elongation kinetics, both in solution and on a surface using a quartz crystal microbalance, this binding is shown to strongly inhibit further growth of the fibrils. The binding is also demonstrated to shift the monomer-fibril equilibrium in favor of dissociation. We believe that this mechanism, by which a sHsp interacts with mature amyloid fibrils, could represent an additional and potentially generic means by which at least some chaperones protect against amyloid aggregation and limit the onset of misfolding diseases.Christopher A. Waudby, Tuomas P.J. Knowles, Glyn L. Devlin, Jeremy N. Skepper, Heath Ecroyd, John A. Carver, Mark E. Welland, John Christodoulou, Christopher M. Dobson and Sarah Meeha
Native disulphide-linked dimers facilitate amyloid fibril formation by bovine milk alpha(S2)-casein
No full textData source: Supplementary information, https://doi.org/10.1016/j.bpc.2020.106530Bovine milk α(S2)-casein, an intrinsically disordered protein, readily forms amyloid fibrils in vitro and is implicated in the formation of amyloid fibril deposits in mammary tissue. Its two cysteine residues participate in the formation of either intra- or intermolecular disulphide bonds, generating monomer and dimer species. X-ray solution scattering measurements indicated that both forms of the protein adopt large, spherical oligomers at 20 °C. Upon incubation at 37 °C, the disulphide-linked dimer showed a significantly greater propensity to form amyloid fibrils than its monomeric counterpart. Thioflavin T fluorescence, circular dichroism and infrared spectra were consistent with one or both of the dimer isomers (in a parallel or antiparallel arrangement) being predisposed toward an ordered, amyloid-like structure. Limited proteolysis experiments indicated that the region from Ala⁸¹ to Lys¹¹³ is incorporated into the fibril core, implying that this region, which is predicted by several algorithms to be amyloidogenic, initiates fibril formation of α(S2)-casein. The partial conservation of the cysteine motif and the frequent occurrence of disulphide-linked dimers in mammalian milks despite the associated risk of mammary amyloidosis, suggest that the dimeric conformation of α(S2)-casein is a functional, yet amyloidogenic, structure.David C. Thorn, Elmira Bahraminejad, Aidan B. Grosas, Tomas Koudelka, Peter Hoffmann, Jitendra P. Mata, Glyn L. Devlin, Margaret Sunde, Heath Ecroyd, Carl Holt, John A. Carve
Overlap in processing advantages for minimal ingroups and the self
No full textAcknowledgements This work was supported by a Medical Research Council Fellowship (MR/P014097/1), a Christ Church Junior Research Fellowship and a Christ Church Research Centre Grant to P. L. L. The Wellcome Centre for Integrative Neuroimaging is supported by core funding from the Wellcome Trust (203139/Z/16/Z). The work was completed in partial fulfilment of a PhD funded through a DSTL studentship by the first author. We thank the late Professor Glyn Humphreys, who initially supervised the wider PhD project that this work formed a part of, for his helpful discussions and input into this research.Peer reviewe
Protein Particulates: Another Generic Form of Protein Aggregation?
No full textAbstractProtein aggregation is a problem with a multitude of consequences, ranging from affecting protein expression to its implication in many diseases. Of recent interest is the specific form of aggregation leading to the formation of amyloid fibrils, structures associated with diseases such as Alzheimer’s disease. The ability to form amyloid fibrils is now regarded as a property generic to all polypeptide chains. Here we show that around the isoelectric point a different generic form of aggregation can also occur by studying seven widely different, nonrelated proteins that are also all known to form amyloid fibrils. Under these conditions gels consisting of relatively monodisperse spherical particulates are formed. Although these gels have been described before for β-lactoglobulin, our results suggest that the formation of particulates in the regime where charge on the molecules is minimal is a common property of all proteins. Because the proteins used here also form amyloid fibrils, we further propose that protein misfolding into clearly defined aggregates is a generic process whose outcome depends solely on the general properties of the state the protein is in when aggregation occurs, rather than the specific amino acid sequence. Thus under conditions of high net charge, amyloid fibrils form, whereas under conditions of low net charge, particulates form. This observation furthermore suggests that the rules of soft matter physics apply to these systems
The Slap’s resonances: Multiculturalism and adolescence in Tsiolkas’ Australia
No full textThis article discusses Australian author Christos Tsiolkas’ novel ‘The Slap’ (2008) and its television adaptation (2011). The latter is situated in relation to Television Studies debates relating to ‘quality’, with elements of the adaptation that enable its categorisation as ‘quality TV’ highlighted. Tsiolkas, whose novels all prominently feature Greek-Australian characters, has described ‘The Slap’ as a response to John Howard’s period as Prime Minister. The article thus examines in detail particular policies produced in Australia during those years, and the competing discourses relating to ‘multiculturalism’ which were in circulation. Drawing on the writings of Ien Ang and John Stratton, as well as David L. Eng, it is argued that both versions of ‘The Slap’ expose faultlines in Australian society relating to race and ethnicity which multiculturalism policies may attempt to paper over and bury. The article also compares and contrasts the two versions of ‘The Slap’, situates the novel in relation to Tsiolkas’ other writings, and positions the adaptation within the landscape of Australian film and television. The essay concludes with a consideration of the significance of music in Tsiolkas’ novels, and how, in particular, this shapes his representations of younger characters
Repetitive transcranial magnetic stimulation attenuates the perception of force output production in non-exercised hand muscles after unilateral exercise
No full textWe examined whether unilateral exercise creates perception bias in the non-exercised limb and ascertained whether rTMS applied to the primary motor cortex (M1) interferes with this perception. All participants completed 4 interventions: 1) 15-min learning period of intermittent isometric contractions at 35% MVC with the trained hand (EX), 2) 15-min learning period of intermittent isometric contractions at 35% MVC with the trained hand whilst receiving rTMS over the contralateral M1 (rTMS+EX); 3) 15-min of rTMS over the ‘trained’ M1 (rTMS) and 4) 15-min rest (Rest). Pre and post-interventions, the error of force output production, the perception of effort (RPE), motor evoked potentials (MEPs) and compound muscle action potentials (CMAPs) were measured in both hands. EX did not alter the error of force output production in the trained hand (Δ3%; P>0.05); however, the error of force output production was reduced in the untrained hand (Δ12%; P0.05). RPE was significantly higher after rTMS+EX in the trained hand (9.2±0.5 vs. 10.7±0.7; P0.05). The novel finding was that exercise alone reduced the error in force output production by over a third in the untrained hand. Further, when exercise was combined with rTMS the transfer of force perception was attenuated. These data suggest that the contralateral M1 of the trained hand might, in part, play an essential role for the transfer of force perception to the untrained hand
Amyloid Fibril-Like Structure Underlies the Aggregate Structure across the pH Range for β-Lactoglobulin
No full textAbstractThe protein β-lactoglobulin aggregates into two apparently distinct forms under different conditions: amyloid fibrils at pH values away from the isoelectric point, and spherical aggregates near it. To understand this apparent dichotomy in behavior, we studied the internal structure of the spherical aggregates by employing a range of biophysical approaches. Fourier transform infrared studies show the aggregates have a high β-sheet content that is distinct from the native β-lactoglobulin structure. The structures also bind the amyloidophilic dye thioflavin-T, and wide-angle x-ray diffraction showed reflections corresponding to spacings typically observed for amyloid fibrils composed of β-lactoglobulin. Combined with small-angle x-ray scattering data indicating the presence of one-dimensional linear aggregates at the molecular level, these findings indicate strongly that the aggregates contain amyloid-like substructure. Incubation of β-lactoglobulin at pH values increasingly removed from the isoelectric point resulted in the increasing appearance of fibrillar species, rather than spherical species shown by electron microscopy. Taken together, these results suggest that amyloid-like β-sheet structures underlie protein aggregation over a much broader range of conditions than previously believed. Furthermore, the results suggest that there is a continuum of β-sheet structure of varying regularity underlying the aggregate morphology, from very regular amyloid fibrils at high charge to short stretches of amyloid-like fibrils that associate together randomly to form spherical particles at low net charge
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