Bacterial in-cell NMR of human α-synuclein: a disordered monomer by nature?

The notion that human alpha-synuclein is an intrinsically disordered monomeric protein was recently challenged by a postulated alpha-helical tetramer as the physiologically relevant protein structure. The fact that this alleged conformation had evaded detection for so many years was primarily attributed to a widely used denaturation protocol to purify recombinant alpha-synuclein. In the present paper, we provide in-cell NMR evidence obtained directly in intact Escherichia coli cells that challenges a tetrameric conformation under native in vivo conditions. Although our data cannot rule out the existence of other intracellular protein states, especially in cells of higher organisms, they indicate clearly that inside E. coli alpha-synuclein is mostly monomeric and disordered.