CLAC binds to aggregated Aβ and Aβ fragments, and attenuates fibril elongation

Deposition of amyloid beta-peptide (A beta) into amyloid plaques is one of the invariant neuropathological features of Alzheimer's disease. Proteins that codeposit with M are potentially important for the pathogenesis, and a recently discovered plaque-associated protein is the collagenous Alzheimer amyloid plaque component (CLAC). In this study, we investigated the molecular interactions between A beta aggregates and CLAC using surface plasmon resonance spectroscopy and a solid-phase binding immunoassay. We found that CLAC binds to A beta with high affinity, that the central region of A beta is necessary and sufficient for CLAC interaction, and that the aggregation state of A beta as well as the presence of negatively charged residues is important. We also show that this binding results in a reduced rate of fibril elongation. Taken together, we suggest that CLAC becomes involved at an intermediate stage in the pathogenesis by binding to A beta fibrils, including fibrils formed from peptides with truncated N- or C-termini, and thereby slows their growth.