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. Author manuscript; available in PMC: 2016 Jun 16.
Published in final edited form as: Nature. 2015 Dec 16;528(7583):580–584. doi: 10.1038/nature16162

Figure 2. The helical repeat protein universe.

Figure 2

a, the geometry of a repeat protein can be described by axial displacement (z), radius of the helix (r) and angular displacement or twist (ω) between repeat units. b, designed helical repeat (DHR) proteins (grey) cover radius and twist ranges not found in native repeat protein families (colors). Designs forming right-handed superhelices have positive ω values; left-handed, negative ω values. Native families abbreviations: ANK, ankyrin; ARM, armadillo; TPR, tetratricopeptide repeat; HAT, half TPR; PPR, pentatricopeptide repeat; HEAT, heat repeat; PUM, pumilio homology domain; mTERF, mitochondrial termination factor; TAL, transcription activator-like effector; OTHER, alpha helical repeat proteins not in the other families. Designs structurally validated by small angle x-ray scattering (SAXS) (black) or crystallography (black with red circle) are distributed throughout the space. On top, representative experimentally validated designs with a variety of shapes.