Characterization of the Alzheimer's disease-associated CLAC protein and identification of an amyloid beta-peptide-binding site.

Amyloid beta-peptide (Abeta) deposition into amyloid plaques is one of the invariant neuropathological features of Alzheimer's disease. Other proteins co-deposit with Abeta in plaques, and one recently identified amyloid-associated protein is the collagen-like Alzheimer amyloid plaque component CLAC. It is not known how CLAC deposition affects Abeta plaque genesis and the progress of the disease. Here, we studied the in vitro properties of CLAC purified from a mammalian expression system. CLAC displays features characteristic of a collagen protein, e.g. it forms a partly protease-resistant triple-helical structure, exhibits an intermediate affinity for heparin, and is glycosylated. Purified CLAC was also used to investigate the interaction between CLAC and Abeta. Using a solid-phase binding assay, we show that CLAC bound with a similar affinity to aggregates formed by Abeta-(1-40) and Abeta-(1-42) and that the interaction was impaired by increasing salt concentrations. An 8-residue-long sequence located in non-collagenous domain 2 of CLAC was found to be crucial for the interaction with Abeta. These findings may be useful for future therapeutic interventions aimed at finding compounds that modulate the binding of CLAC to Abeta deposits.