Solution conditions define morphological homogeneity of α-synuclein fibrils

The intrinsically disordered human α-synuclein (αSyn) protein exhibits considerable heterogeneity in in vitro fibrillization reactions. Using atomic force microscopy (AFM) we show that depending on the solvent conditions, A140C mutant and wild-type αSyn can be directed to reproducibly form homogeneous populations of fibrils exhibiting regular periodicity. Results from Thioflavin-T fluorescence assays, determination of residual monomer concentrations and native polyacrylamide gel electrophoresis reveal that solvent conditions including EDTA facilitate incorporation of a larger fraction of monomers into fibrils. The fibrils formed in 10mM Tris-HCl, 10mM NaCl and 0.1mM EDTA at pH7.4 display a narrow distribution of periodicities with an average value of 102±6nm for the A140C mutant and 107±9nm for wt αSyn. The ability to produce a homogeneous fibril population can be instrumental in understanding the detailed structural features of fibrils and the fibril assembly process. Moreover, the availability of morphologically well-defined fibrils will enhance the potential for use of amyloids as biological nanomaterials.