Dissecting the Structural Organization of Multiprotein Amyloid Aggregates Using a Bottom-Up Approach

Deposition of fibrillar amyloid beta (A beta) in senile plaques is a pathological signature of Alzheimer's disease. However, senile plaques also contain many other components, including a range of different proteins. Although the composition of the plaques can be analyzed in post-mortem tissue, knowledge of the molecular details of these multiprotein inclusions and their assembly processes is limited, which impedes the progress in deciphering the biochemical mechanisms associated with A beta pathology. We describe here a bottom-up approach to monitor how proteins from human cerebrospinal fluid associate with A beta amyloid fibrils to form plaque particles. The method combines flow cytometry and mass spectrometry proteomics and allowed us to identify and quantify 128 components of the captured multiprotein aggregates. The results provide insights into the functional characteristics of the sequestered proteins and reveal distinct interactome responses for the two investigated A beta variants, A beta(1-40) and A beta(1-42). Furthermore, the quantitative data is used to build models of the structural organization of the multiprotein aggregates, which suggests that A beta is not the primary binding target for all the proteins; secondary interactions account for the majority of the assembled components. The study elucidates how different proteins are recruited into senile plaques and establishes a new model system for exploring the pathological mechanisms of Alzheimer's disease from a molecular perspective.