Fig. 2.

The structure and mechanism of auxin action. A: crystal structure of Arabidopsis SKP1 (ASK1)-TIR1-inositol hexakisphosphate (IP6) in complex with auxin and an AUX/IAA domain II peptide. Both ASK1 (magenta) and TIR1 (blue) are shown in ribbon. Auxin is shown in space-filled model (green and red spheres). The AUX/IAA peptide (orange) and IP6 (red) are shown in sticks. B: a schematic diagram showing how auxin is sensed by TIR1 with the assistance of IP6 and how the hormone promotes TIR1-AUX/IAA interactions. LRRs, leucine-rich repeats.