Predicting conformational entropy of bond vectors in proteins by networks of coupled rotators

In this article, a formal expression for the conformational entropy of a bond vector in a protein is derived using the networks of coupled rotators model for the description of internal dynamics. Analytical relationships between NMR order parameters and conformational entropies are derived, and the possibility to extract the latter from NMR experiments is discussed. These results are illustrated in the case of the calcium-binding protein calbindin. (C) 2008 American Institute of Physics

The Significance of the Location of Mutations for the Native-State Dynamics of Human Lysozyme

peer reviewe

Hsp70 Oligomerization Is Mediated by an Interaction between the Interdomain Linker and the Substrate-Binding Domain

Oligomerization in the heat shock protein (Hsp) 70 family has been extensively documented both in vitro and in vivo, although the mechanism, the identity of the specific protein regions involved and the physiological relevance of this process are still unclear. We have studied the oligomeric properties of a series of human Hsp70 variants by means of nanoelectrospray ionization mass spectrometry, optical spectroscopy and quantitative size exclusion chromatography. Our results show that Hsp70 oligomerization takes place through a specific interaction between the interdomain linker of one molecule and the substrate-binding domain of a different molecule, generating dimers and higher-order oligomers. We have found that substrate binding shifts the oligomerization equilibrium towards the accumulation of functional monomeric protein, probably by sequestering the helical lid sub-domain needed to stabilize the chaperone: substrate complex. Taken together, these findings suggest a possible role of chaperone oligomerization as a mechanism for regulating the availability of the active monomeric form of the chaperone and for the control of substrate binding and release. © 2013 Aprile et al.FAA was recipient of a graduate fellowship from the Italian Ministry of Education, University and Research. AD is grateful for support from Murray Edwards College, Cambridge, through a Junior Research Fellowship. FS is a Sir Henry Wellcome Fellow. CR acknowledges financial support by the Spanish Ministry of Health according to the 'Plan Nacional de I+D+I 2008-2011', through ISCIII with cofunding by FEDER (CP10/00527). JLPB is a Royal Society University Research Fellow. FAA and PT are grateful for support from Regione Lombardia (NEDD and >Network Tecnologico integrato per lo studio proteomico e trascrittomico di malattie neurodegenerative correlate a deposizioni di amiloidi>). CMD acknowledges support from BBSRC (BB/E019927/1), the Wellcome Trust (094425/Z/10/Z), the European Commission (project LSHM-CT-2006-037525). NC acknowledges support from Human Frontiers Science Program (HFSP) through a Long-term Fellowship (LT000795/2009).Peer Reviewe

Application of Lysine-specific Labeling to Detect Transient Interactions Present During Human Lysozyme Amyloid Fibril Formation.

Populating transient and partially unfolded species is a crucial step in the formation and accumulation of amyloid fibrils formed from pathogenic variants of human lysozyme linked with a rare but fatal hereditary systemic amyloidosis. The partially unfolded species possess an unstructured β-domain and C-helix with the rest of the α-domain remaining native-like. Here we use paramagnetic relaxation enhancement (PRE) measured by NMR spectroscopy to study the transient intermolecular interactions between such intermediate species. Nitroxide spin labels, introduced specifically at three individual lysine residues, generate distinct PRE profiles, indicating the presence of intermolecular interactions between residues within the unfolded β-domain. This study describes the applicability to PRE NMR measurements of selective lysine labeling, at different sites within a protein, as an alternative to the introduction of spin labels via engineered cysteine residues. These results reveal the importance of the β-sheet region of lysozyme for initiating self-assembly into amyloid fibrils

Local Cooperativity in an Amyloidogenic State of Human Lysozyme Observed at Atomic Resolution

The partial unfolding of human lysozyme underlies its conversion from the soluble state into amyloid fibrils observed in a fatal hereditary form of systemic amyloidosis. To understand the molecular origins of the disease, it is critical to characterize the structural and physicochemical properties of the amyloidogenic states of the protein. Here we provide a high-resolution view of the unfolding process at low pH for three different lysozyme variants, the wild-type protein and the mutants I56T and I59T, which show variable stabilities and propensities to aggregate in vitro. Using a range of biophysical techniques that includes differential scanning calorimetry and nuclear magnetic resonance spectroscopy, we demonstrate that thermal unfolding under amyloidogenic solution conditions involves a cooperative loss of native tertiary structure, followed by progressive unfolding of a compact, molten globule-like denatured state ensemble as the temperature is increased. The width of the temperature window over which the denatured ensemble progressively unfolds correlates with the relative amyloidogenicity and stability of these variants, and the region of lysozyme that unfolds first maps to that which forms the core of the amyloid fibrils formed under similar conditions. Together, these results present a coherent picture at atomic resolution of the initial events underlying amyloid formation by a globular protein

Inhibition of α-Synuclein Fibril Elongation by Hsp70 Is Governed by a Kinetic Binding Competition between α-Synuclein Species.

The Hsp70 family of chaperones plays an essential role in suppressing protein aggregation in the cell. Here we investigate the factors controlling the intrinsic ability of human Hsp70 to inhibit the elongation of amyloid fibrils formed by the Parkinson's disease-related protein α-synuclein. Using kinetic analysis, we show that Hsp70 binds preferentially to α-synuclein fibrils as a consequence of variations in the association and dissociation rate constants of binding to the different aggregated states of the protein. Our findings illustrate the importance of the kinetics of binding of molecular chaperones, and also of potential therapeutic molecules, in the efficient suppression of specific pathogenic events linked to neurodegeneration.BBSRC (BB/J002119/1), European Research Council (337969

Substrate binding affects the oligomerization equilibrium.

<p>(A) Fluorescence titration of the binding of the NR peptide to the different Hsp70 constructs (showing the fraction of bound substrate as a function of chaperone concentration): SBD556 (red circles), native (green circles) and refolded (brown circles) SBD641, ΔLSBD641 (black circles), and FL-Hsp70 (blue circles). The continuous lines represent the best fits of the data to a single binding site model. (B) SEC analysis of SBD641 in the absence (green line) and the presence (orange line) of a 14-fold excess of NR peptide. (C) nESI MS spectrum of SBD641 in the presence of the NR peptide at a protein:peptide ratio of 1:1 at a sample cone voltage of 60 V. Inset is the region of the spectrum showing dimers, at increasing sample cone voltages from front to back. The coloured circles represent charge states that correspond to the same protein species: uncomplexed monomeric protein in dark green, monomeric SBD641 complexed with the NR peptide in light green, the uncomplexed dimeric protein in red, dimeric SBD641 complexed with a single NR peptide molecule in pink, and dimeric SBD641 complexed with two NR peptide molecules in orange. The protein: peptide molar ratio used allowed sufficient resolution of the various charge state series for unambiguous assignment of substrate-bound chaperone states, which are validated by the successive removal of peptide equivalents upon increasing collisional activation (inset). The spectra shown are representative of five repeats, each incorporating >150 scans, with the relative abundances of apo- and holo-forms varying by <5% between individual nanoESI injections. Observed masses differ from those expected, due to residual adduction of solvent molecules and buffer ions, by <1%, as is typical in the spectra of non-covalent complexes (Table S6 in File S1) [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0067961#B57" target="_blank">57</a>].</p