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.
Department of Chemistry, University of Cambridge, UK.
Anne
A
Dhulesia
Nunilo
N
Cremades
Janet R
JR
Kumita
Shang-Te Danny
ST
Hsu
Maria F
MF
Mossuto
Mireille
M
Dumoulin
Daniel
D
Nietlispach
Mikael
M
Akke
Xavier
X
Salvatella
Christopher M
CM
Dobson
D000682:Amyloid / Q000737:chemistry*; D014644:Genetic Variation; D006801:Humans; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D009113:Muramidase / Q000737:chemistry* / Q000235:genetics; D009154:Mutation; D017510:Protein Folding
D000682:Amyloid; D009113:Muramidase