[The effect of red pigment on amyloidization of yeast proteins]

Abstract

Amyloid bound thioflavine T fluorescence was studied in the lysates of yeast strains carrying mutations in genes ADE1 or ADE2 and accumulating red pigment, a result of polymerization of aminoimidazoleribotide (an intermediate of adenine biosynthesis). The fluorescence is drastically enhanced in the case of cells grown in media containing high concentration of adenine (100 mg/l) that blocks accumulation of red pigment. Blocks at first stages of purine biosynthesis de novo also impede red pigment and lead to the same effect on thioflavine fluorescence. At the same time induction of mutations in genes ADE1 or ADE2 in originally white prototrophic strains leads to considerable drop of fluorescence. A fraction of protein polymers was studied by agarose gel electrophoresis and this permitted to conclude that lowering of fluorescence intensity is indeed connected with the decrease of amyloid amount in cells accumulating red pigment. Model experiments with insulin fibers demonstrate that red pigment binds fibrils and blocks their interaction with Thioflavine T. 2D-electrophoretic comparison of pellet proteins of red and white isogenic strains, followed by MALDI, allowed identification of 23 pigment-dependent proteins. These proteins mostly belong to functional classes of chaperones and proteins, involved in glucose metabolism, closely corresponding to prion-dependent proteins characterized in our previous work. We suppose that, binding amyloid fibrils, red pigment hinders formation of prion aggregates and also, blocking fibril contact with chaperones, impedes prion propagation.