ИСТИНА

The toxic effect of alpha-synuclein oligomers is known to be due to their participation in the formation of pores in the cell membrane of neurons and the subsequent changes in ion transport. As a result of these processes, an increase in the content of calcium ions in the cytosol could activate basic forms of NO-synthase and thereby increase the production of NO. In turn, nitric oxide can increase the production of superoxide by inhibiting the mitochondrial respiratory chain, which might initialize the processes of nitration and oxidation of other proteins. We studied the effect of point substitution of a tyrosine residue for a cysteine residue, generating dimeric forms of alpha-synuclein, and its posttranslational modifications (glycation and oxidation) on the amyloid transformation of alpha-synuclein. The wild-type and Cys136-containing fractions of alpha-synuclein were separated using thiol-Sepharose. In the absence of reducing agents, Cys136-AS forms dimers due to the disulfide bonding. Both wild-type and Cys136 alpha-synuclein preparations are prone to aggregate during prolonged incubation under shaking at pH 4 and 37°C, but the aggregates produced by either monomeric or dimeric Cys136-AS do not exhibit amyloid properties according to the test with Thioflavin T. Moreover, an admixture of dimeric Cys136-AS prevents the amyloid transformation of the wild-type alpha-synuclein. Glycation of alpha-synuclein by methylglyoxal stimulates protein aggregation, but prevents it amyloid transformation. We suppose that the effect of point substitutions of amino acids stimulating the formation of dimers as well as post-translational modifications of alpha-synuclein should be taken into account to avoid erroneous interpretation of experiments on amyloid transformation of this protein. This work was supported by Russian Scientific Foundation (grant № 16-14-10027).