Fig. 1: AUX/IAA proteins are intrinsically disordered outside the PB1 domain.

a Simplified phylogenetic tree (with average branch length depicted) of 29 Arabidopsis thaliana AUX/IAAs showing their sequence composition based on IUPred2A prediction for disorder (score classification: disorder (dark lilac): >0.6; intermediate (light lilac): 0.4–0.6; ordered (white): <0.4). Outer circles correspond to full length proteins, inner circles represent disorder prediction excluding the PB1 domain (scale shows width per 100 AA). b In silico prediction maps of disorder along the IAA7 (orange) and IAA12 (aquamarine) sequence using SPOT, IUPRED1, and PrDos algorithms. AUX/IAA domain structure (Domain I (DI), a linker, a core degron, a degron tail and the Phox/Bem1p (PB1) domain) are displayed. Outer plots represent Kyte-Doolittle hydropathy (scale from −4 to +4). Dotted line in PrDos prediction represents a 0.5 threshold. c Circular dichroism spectra of IAA7 (orange) and IAA12 (aquamarine) oligomerization-deficient (solid lines) and PB1-less variants (dashed colored lines) show the lack of defined secondary structure elements outside of the PB1 domain. Reference spectra (black dotted lines) are depicted. Ellipticity is calculated as mean residual ellipticity (MRE). Shown is the mean of three independent experiments (n = 3). d IAA7 (orange) and IAA12 (aquamarine) exhibit an extended fold according to Stokes radii determination via size exclusion chromatography. Theoretical Stokes radii of known folds (lilac color gradient, labeled rectangles): intrinsically disordered protein (IDP, dark lilac), premolten globule (PMG, light lilac), molten globule (MG, light lilac), natively folded (NF, white) plus 10% outer limits, and experimental values (colored box plots with whiskers = ~25% (1.5*IQR) of the data points (gray dots); Outliers shown as colored dots; n = 4, 5, 7, and 10 correspondingly for IAA12^ΔPB1, IAA7^ΔPB1, IAA12^BM3, IAA7^BM3).