Elucidating the Mechanism of Amyloid Formation by Human Lysozyme

Lead Research Organisation: University of Cambridge
Department Name: Chemistry

Abstract

Our bodies contain some 100,000 proteins that enable or regulate essentially every chemical or biochemical process on which our lives depend. Under normal circumstances these proteins remain in their soluble functional states, but under other circumstances, for example as a result of mutations or even the impairment of regulating processes, they can form large insoluble aggregates that are non-functional and even toxic. This process is of great importance because it is the underlying origin of a range of debilitating human disorders, including neurodegenerative conditions such as Alzheimer's disease, the transmissible spongiform encephalopathies (such as CJD, the human analogue of 'mad cow disease'), type 2 (late onset) diabetes and systemic pathologies in which large quantities, sometimes kilograms, of protein are deposited in vital organs such as the kidney, heart and liver. In each of these diseases, a single protein undergoes a structural transition, often resulting in the formation of thread-like aggregates known as amyloid fibrils. Many of these diseases are linked to the ageing process, and as a large fraction of the world's population lives to ages unprecedented in human history, these diseases are emerging as among the most feared and debilitating in the modern world. In recent years, much research has focused on understanding what causes proteins to misfold and form amyloid structures, and on the specific mechanism by which such transitions occur. Nevertheless, as a result of structural heterogeneity, low populations and a transient nature, obtaining detailed information about this process has presented a formidable challenge. The primary objective of this study is to elucidate structural information of the different species that are populated along the aggregation pathway of human lysozyme. As well as being associated with a systemic amyloid disorder, lysozyme is one of the most highly studied of all proteins providing a unique opportunity to probe the difference between normal and aberrant behaviour at atomic resolution. By studying species populated under fibril forming conditions, we will be able to begin to understand not only the structures of intermediate species, but also the dynamics of the conversion between the different states involved in fibril formation. These studies should generate a sufficiently profound understanding of the distinctive differences between species involved in normal and aberrant folding behaviour to contribute significantly to the identification of novel strategies through which rational therapeutic intervention could lead to prevention or treatment, not just of this specific disease, but also perhaps the entire family of protein misfolding disorders.

Technical Summary

The overall objective of this study is to understand how soluble proteins convert into amyloid fibrils. We intend to achieve this aim by determining the structural features of the transient species which are populated throughout fibril formation, and to gain an understanding of the dynamic interactions between these states in unprecedented detail. In this study, we will generate mutational lysozyme variants to vary the population of the transient species. We will also employ naturally occurring (i.e. chaperones) and engineered biomolecules (i.e. antibody fragments) that interact with species along the aggregation pathway to try and trap these species for analysis. Once methods are established to populate these species, we will study the system under fibril forming conditions and in a time dependent manner, using an array of established biophysical techniques, in particular exploiting recent advances in NMR spectroscopy and nanospray mass spectrometry. We have established NMR relaxation techniques that probe the structures and stabilities of transient protein folding intermediates with populations as low as 1% that are in dynamic equilibrium with other states. We have also developed mass spectrometry methods for detecting protein assemblies exceeding 1 MDa in size, along with procedures that enable us to define both the stoichiometric and topological arrangement within such complexes. We shall use both these approaches to probe the nature and populations of oligomeric intermediates in lysozyme aggregation, along with similar studies of the species formed on interaction with other macromolecules. These complementary spectroscopic methods, along with our established ability to use theoretical and computational techniques for interpreting these types of data gives us an unrivalled opportunity to define the structural and dynamic character of fibril formation by a globular protein and to explore the manner in which such a process can be controlled or inhibited.

Publications


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Brorsson AC (2010) Methods and models in neurodegenerative and systemic protein aggregation diseases. in Frontiers in bioscience (Landmark edition)
Buell AK (2011) Population of nonnative states of lysozyme variants drives amyloid fibril formation. in Journal of the American Chemical Society
Chen SW (2015) Structural characterization of toxic oligomers that are kinetically trapped during a-synuclein fibril formation. in Proceedings of the National Academy of Sciences of the United States of America
 
Description 1) We engineered a novel mutation into lysozyme (I59T) to provide an additional tool for comparison with the wild-type and amyloidogenic variants of lysozyme. These variants were used for comparative NMR and QCM studies to elucidate the structure, on a residual level, of a partially unfolded intermediate state important for the initial events of amyloid formation and to correlate these structural features with protein aggregation.



2) We applied complimentary biophysical techniques to gain str
Exploitation Route This study has generated a greater understanding of the distinctive differences between species involved in normal and aberrant folding behaviour and we hope that it can contribute to the identification of novel strategies through which rational therapeutic intervention could lead to prevention or treatment, not just of lysozyme amyloidosis, but also perhaps the entire family of protein misfolding disorders.
Sectors Chemicals,Pharmaceuticals and Medical Biotechnology
 
Description Collaboration with Prof. Mark Wilson, University of Wollongong, Australia 
Organisation University of Wollongong
Country Australia, Commonwealth of 
Sector Academic/University 
PI Contribution We have also established a strong collaboration with the research group of Prof. Mark Wilson at the University of Wollongong, NSW, Australia. Through this collaboration, we have demonstrated that extracellular chaperones (clusterin, haptoglobin and alpha2-macroglobulin) can inhibit in vitro lysozyme fibril formation when present at highly substoichiometric concentrations and the mechanism by which these chaperones act is through interactions with soluble oligomeric species present during aggregation (Yerbury et al., FASEB J., 2007; Kumita et al, JMB, 2007, Yerbury et al., JBC, 2009).
Start Year 2002