Intrinsic disorder and conformational coexistence in auxin coreceptors

Sigurd Ramans-Harborough, Arnout P. Kalverda, Iain W. Manfield, Gary S. Thompson, Martin Kieffer, Veselina Uzunova, Mussa Quareshy, Justyna M. Prusinska, Suruchi Roychoudhry, Ken-ichiro Hayashi, Richard Napier, Charo del Genio, Stefan Kepinski

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AUXIN/INDOLE 3-ACETIC ACID (Aux/IAA) transcriptional repressor proteins and the TRANSPORT INHIBITOR RESISTANT 1/AUXIN SIGNALING F-BOX (TIR1/AFB) proteins to which they bind act as auxin coreceptors. While the structure of TIR1 has been solved, structural characterization of the regions of the Aux/IAA protein responsible for auxin perception has been complicated by their predicted disorder. Here, we use NMR, CD and molecular dynamics simulation to investigate the N-terminal domains of the Aux/IAA protein IAA17/AXR3. We show that despite the conformational flexibility of the region, a critical W–P bond in the core of the Aux/IAA degron motif occurs at a strikingly high (1:1) ratio of cis to trans isomers, consistent with the requirement of the cis conformer for the formation of the fully-docked receptor complex. We show that the N-terminal half of AXR3 is a mixture of multiple transiently structured conformations with a propensity for two predominant and distinct conformational subpopulations within the overall ensemble. These two states were modeled together with the C-terminal PB1 domain to provide the first complete simulation of an Aux/IAA. Using MD to recreate the assembly of each complex in the presence of auxin, both structural arrangements were shown to engage with the TIR1 receptor, and contact maps from the simulations match closely observations of NMR signal-decreases. Together, our results and approach provide a platform for exploring the functional significance of variation in the Aux/IAA coreceptor family and for understanding the role of intrinsic disorder in auxin signal transduction and other signaling systems.
Original languageEnglish
Article numbere2221286120
Number of pages11
JournalProceedings of the National Academy of Sciences
Issue number40
Early online date27 Sept 2023
Publication statusPublished - 3 Oct 2023

Bibliographical note

This open access article is distributed under Creative Commons Attribution License 4.0 (CC BY).


We acknowledge the University of Leeds NMR facility for access to the 950-MHz and 600-MHz spectrometers funded by the University of Leeds and the 750-MHz spectrometer funded by the Wellcome Trust (Award Reference: 094232). This research was funded by grants from the Biotechnology and Biological Sciences Research Council (Award references: BB/L010623/1 to S.K. and R.N., and BB/I532402/1 to S.R.-H.) and Syngenta UK (Award Reference: 1232512 to S.K. and S.R.-H.). CIDG acknowledges the support from UKRI under Future Leaders Fellowship grant number MR/T020652/1.


  • auxin
  • disorder
  • Aux/IAA
  • TIR1
  • IDP


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