α-synuclein ~4: tau ~6 nm
||Theillet FX et al., Physicochemical properties of cells and their effects on intrinsically disordered proteins (IDPs). Chem Rev. 2014 Jul 9 114(13):6661-714. doi: 10.1021/cr400695p p.6667 right column bootom paragraphPubMed ID24901537
|| Li J, Uversky VN, Fink AL. Effect of familial Parkinson's disease point mutations A30P and A53T on the structural properties, aggregation, and fibrillation of human alpha-synuclein. Biochemistry. 2001 Sep 25 40(38):11604-13  Mukrasch MD et al., Structural polymorphism of 441-residue tau at single residue resolution. PLoS Biol. 2009 Feb 17 7(2):e34. doi: 10.1371/journal.pbio.1000034PubMed ID11560511, 19226187
||Primary source  abstract: "A variety of biophysical methods, including far-UV circular dichroism, FTIR [Fourier-transform infrared spectroscopy], small-angle X-ray scattering, and light scattering, were employed." Primary source  abstract: "Here [investigators] show that it is possible to overcome the size limitations that have traditionally hampered detailed nuclear magnetic resonance (NMR) spectroscopy studies of such large nonglobular proteins [as tau]. This is achieved using optimal NMR pulse sequences and matching of chemical shifts from smaller segments in a divide and conquer strategy."
||P.6667 right column bottom paragraph: "The hydrodynamic radii of most disordered proteins are in the range of these correlation lengths. 140 residue α-synuclein has a radius of ∼4 nm (primary source 171), whereas tau (441 residues) has a radius of ∼6 nm (primary source 172). According to the correlation length model, and provided that intracellular crowding does not significantly change the hydrodynamic radii of these IDPs (intrinsically disordered proteins), both proteins experience an intracellular microviscosity inside E. coli and mammalian cells that is 8- and 3-times greater than in buffer, respectively. Because both radii are representative for many disordered proteins, these approximate values are likely to be generally valid (refs 173, 174)." Please note-both primary sources seem to have been studying human proteins.