Stepwise unfolding of human β-microglobulin into a disordered amyloidogenic precursor at low pH.

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Bibliographic Details
Title:	Stepwise unfolding of human β-microglobulin into a disordered amyloidogenic precursor at low pH.
Authors:	Narang, Dominic¹, Singh, Anubhuti², Mukhopadhyay, Samrat mukhopadhyay@iisermohali.ac.in
Source:	European Biophysics Journal. Jan2017, Vol. 46 Issue 1, p65-76. 12p.
Subjects:	Microglobulins, Protein folding, Amyloid beta-protein, Protein precursors, Amyloidosis, Dialysis (Chemistry)
Abstract:	Amyloid fibril formation by human β-microglobulin (βm) is associated with dialysis-related amyloidosis. In order to understand the mechanism of protein misfolding, it is important to characterize the nature and properties of various intermediates formed during protein unfolding. In this work, we studied the effect of pH change on the unfolding of βm using a range of spectroscopic readouts. In order to investigate the local structural changes, we created single tryptophan (W60 and W95) mutants of βm. The equilibrium results suggested that in the acid-unfolded state of βm at pH 2.5, the W60 residue attains non-native local structure whereas the W95 residue becomes more exposed. Our stopped-flow kinetic data revealed that βm undergoes unfolding in a stepwise manner. Initial unfolding of βm involves non-uniform protein expansion with the unpacking of tertiary structure and significant core solvation while maintaining a native-like structure around residue W95. The resolved-phase of unfolding exhibits a timescale of ~500 ms that describes the transition from the native-like swollen intermediate to an acid-induced disordered state. Taken together, our results demonstrate that βm has a complex pH-induced unfolding mechanism yielding a disordered amyloidogenic precursor comprising both exposed and buried segments. [ABSTRACT FROM AUTHOR]
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Database:	Engineering Source

Description
Abstract:	Amyloid fibril formation by human β-microglobulin (βm) is associated with dialysis-related amyloidosis. In order to understand the mechanism of protein misfolding, it is important to characterize the nature and properties of various intermediates formed during protein unfolding. In this work, we studied the effect of pH change on the unfolding of βm using a range of spectroscopic readouts. In order to investigate the local structural changes, we created single tryptophan (W60 and W95) mutants of βm. The equilibrium results suggested that in the acid-unfolded state of βm at pH 2.5, the W60 residue attains non-native local structure whereas the W95 residue becomes more exposed. Our stopped-flow kinetic data revealed that βm undergoes unfolding in a stepwise manner. Initial unfolding of βm involves non-uniform protein expansion with the unpacking of tertiary structure and significant core solvation while maintaining a native-like structure around residue W95. The resolved-phase of unfolding exhibits a timescale of ~500 ms that describes the transition from the native-like swollen intermediate to an acid-induced disordered state. Taken together, our results demonstrate that βm has a complex pH-induced unfolding mechanism yielding a disordered amyloidogenic precursor comprising both exposed and buried segments. [ABSTRACT FROM AUTHOR]
ISSN:	01757571
DOI:	10.1007/s00249-016-1138-x