Isolation of Streptomyces sp. KK65 as a produceer of β-amyloid aggregation inhibitor

β-amyloid (Aβ) peptides from the proteolytic processing of β-amyloid precursor protein (β-APP) aggregates in the brain to form senile plaques, and their aggregation plays a key role in pathogenesis of Alzheimer's disease (AD). To isolate an active compound that has an Aβ aggregation-inhibitory activity, 2,000 microbial metabolite libraries were screened based on their ability to inhibit Aβ aggregation by using both Congo red and thioflavin T assays. As a result, a water-soluble fraction of a soil microorganism, KK565, showed a potent Aβ aggregation-inhibitory activity. The strain was identified as Streptomyces species, based on the cultural and morphological characteristics, the presence of diaminopimelic acid in the cell wall, and the sugar patterns for the whole-cell extract. In addition, the purification of active principle resulted in identifying a heat-unstable protein responsible for the Aβ aggregation-inhibitory activity.