Structural Characterization of the Pre-Amyloid Oligomers of β-2-Microglobulin Using Covalent Labeling and Mass Spectrometry
Date of Award
Open Access Dissertation
Doctor of Philosophy (PhD)
Richard W. Vachet
Lila M. Gierasch
Igor A. Kaltashov
The initial steps involved in the assembly of normally soluble proteins into amyloid fibrils remain unclear, yet over 20 human diseases are associated with proteins that aggregate in this manner. Protein surface modification is a potential means of mapping the interaction sites in early oligomers that precede amyloid formation. This dissertation focuses on the use of covalent labeling combined with mass spectrometry to elucidate the structural features of Cu(II)-induced β-2-microglobulin (β2m) amyloid formation. An improved covalent modification and MS-based approach for protein surface mapping has been developed to address the need for a reliable approach that ensures protein structural integrity during labeling experiments and provides readily detectable modifications. This approach involves measuring the kinetics of the modification reactions and allows any local perturbations caused by the covalent label to be readily identified and avoided. This MS-based method has been used to study human β2m, a monomeric protein that has been shown to aggregate into amyloid fibrils in dialysis patients leading to dialysis-related amyloidosis. Under conditions that lead to β2m amyloid formation, reactions of β2m with three complementary covalent labels have been used to identify the Cu(II) binding site, metal-induced conformational changes, and the oligomeric interfaces. Results confirm that Cu(II) binds to His31 and the N-terminal amine. Binding to these residues causes several structural changes in the N-terminal region and ABED β-sheet which likely enables formation of oligomeric intermediates. The covalent labeling data indicate that the pre-amyloid β2m dimer has an interface that involves the antiparallel arrangement of ABED sheets from two monomers. Moreover, our covalent labeling data allowed us to develop a model for the tetramer in which the interface is mediated by interactions between D strands of one dimer unit and the G strands of another dimer unit. Lastly, the selective covalent modification approach has been used to delineate the structural changes in β2m after interaction with Cu(II), Ni(II), and Zn(II) and their effect on its aggregation. Our covalent labeling data indicates that the unique effect of Cu(II) appears to be caused by the site at which the metal binds the protein and the conformational changes it induces.
Mendoza, Vanessa Leah Castillo, "Structural Characterization of the Pre-Amyloid Oligomers of β-2-Microglobulin Using Covalent Labeling and Mass Spectrometry" (2010). Open Access Dissertations. 293.