Instability, unfolding and aggregation of human lysozyme variants underlying amyloid fibrillogenesis

Abstract

Tissue deposition of soluble proteins as amyloid fibrils underlies a range of fatal diseases. The two naturally occurring human lysozyme variants are both amyloidogenic, and are shown here to be unstable. They aggregate to form amyloid fibrils with transformation of the mainly helical native fold, observed in crystal structures, to the amyloid fibril cross-beta fold. Biophysical studies suggest that partly folded intermediates are involved in fibrillogenesis, and this may be relevant to amyloidosis generally.

Probing the origins, diagnosis and treatment of amyloid diseases using antibodies

“…The additional peak (coloured in yellow) has been shown to result from a locally cooperative unfolding event, identified as the unfolding of the b-domain and the C-helix of the variant protein molecule [117]. From this result, and those of previous studies [18,117,118], a mechanism of fibril formation has been proposed for lysozyme (red box). As a result of its reduced stability and global cooperativity, the D67H variant protein populates transiently a partially unfolded intermediate (species I) in which the three helices that form the core of the a-domain still have native-like structure, whereas the b-domain and the C-helix are substantially disordered.…”

“…In such species, the peptide or protein involved exposes at least part of its main chain and hydrophobic residues to the solvent under conditions in which intermolecular interactions can take place. In the case Textbox 1 of globular proteins, the formation of amyloidogenic intermediates involves the disruption of the native structure to a greater or lesser extent [18][19][20]; in natively unfolded proteins or unstructured peptides, this step may involve the formation of partially folded species with a high propensity to aggregate [21,22]. The second step is the self-association of the Fig.…”

The folding process of hen lysozyme: a perspective from the ‘new view’

“…In particular, it is clear that native-like secondary structure and an overall native fold, revealed by highly protected amide hydrogens, can form during folding in the absence of the close packing and high cooperativity that are characterized by the near-UV CD and fluorescence properties of aromatic residues. Such intermediate species, which have been observed for a number of proteins [40,41], have become of particular interest in the case of lysozyme, not just because of the insight that they give into the nature of the folding process, but also because their stabilization in variant forms of the human protein resulting from single point mutations has recently been implicated in the formation of fibrils associated with familial amyloidosis [42]. Further study of the folding of model systems such as lysozyme, therefore, promises to have significance beyond that associated with the unravelling of the fundamental principles of folding.…”

Spontaneous Fibril Formation by Polyalanines; Discontinuous Molecular Dynamics Simulations

“…Although little is known about the molecular basis for fibrillization, tantalizing clues emerge when the common features of the various amyloidoses are examined. Fibrils of amyloidogenic proteins formed in vitro exhibit strikingly similar morphologies despite a lack of similarity in their sequence, structure and function 4,[6][7][8][9] . They are invariably long, straight and unbranched, and consist of two or more smaller fibrils, called protofilaments (and sometimes protofibrils) which are themselves long ribbons of layered crossed β-sheets propagating along the fibril axis [10][11][12][13][14][15] .…”