Analysis of S100 oligomers and amyloids.

The S100 proteins are a large family of 10-12 kDa EF-hand signaling proteins that bind calcium, and in some cases zinc and copper, functioning as central regulators in a diversity of cellular processes. These proteins have tissue, cell, and subcellular-specific expression patterns, and many have an extracellular function. Altogether, these properties underlie their functional diversity and involvement in several pathological conditions including cancer, inflammation, and neurodegeneration. S100 proteins exhibit considerable structural plasticity, being able to exist as monomers or assemble into dimers, higher oligomers, and amyloids, frequently in a metal-dependent manner. Many of these oligomers are functionally relevant, and S100 amyloids have been recently found in prostatic inclusions. Here, we report experimental procedures for the isolation and quantitation of S100 oligomers from tissues, purification of recombinant human S100 protein for assays and use as standards, and an amyloidogenesis assay that allows monitoring the formation of S100 β-oligomers and amyloids in apo- and metal-bound S100 proteins.