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Flexibility of intrinsically disordered degrons in AUX/IAA proteins reinforces auxin co-receptor assemblies

By Michael Niemeyer, Elena Moreno Castillo, Christian H. Ihling, Claudio Iacobucci, Verona Wilde, Antje Hellmuth, Wolfgang Hoehenwarter, Sophia L. Samodelov, Matias D. Zurbriggen, Panagiotis Kastritis, Andrea Sinz, Luz Irina A. Calderón Villalobos

Posted 30 Sep 2019
bioRxiv DOI: 10.1101/787770 (published DOI: 10.1038/s41467-020-16147-2)

Cullin RING-type E3 ubiquitin ligases SCFTIR1/AFB1-5 and their ubiquitylation targets, AUX/IAAs, sense auxin concentrations in the nucleus. TIR1 binds a surface-exposed degron in AUX/IAAs promoting their ubiquitylation and rapid auxin-regulated proteasomal degradation. Here, we resolved TIR1·auxin·IAA7 and TIR1·auxin·IAA12 complex topology, and show that flexible intrinsically disordered regions (IDRs) in the degron’s vicinity, cooperatively position AUX/IAAs on TIR1. The AUX/IAA PB1 interaction domain also assists in non-native contacts, affecting AUX/IAA dynamic interaction states. Our results establish a role for IDRs in modulating auxin receptor assemblies. By securing AUX/IAAs on two opposite surfaces of TIR1, IDR diversity supports locally tailored positioning for targeted ubiquitylation, and might provide conformational flexibility for adopting a multiplicity of functional states. We postulate IDRs in distinct members of the AUX/IAA family to be an adaptive signature for protein interaction and initiation region for proteasome recruitment.

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