title: Structural basis for the auxin-induced transcriptional regulation by Aux/IAA17.
abstract: Auxin is the central hormone that regulates plant growth and organ development. Transcriptional regulation by auxin is mediated by the auxin response factor (ARF) and the repressor, AUX/IAA. Aux/IAA associates with ARF via domain III-IV for transcriptional repression that is reversed by auxin-induced Aux/IAA degradation. It has been known that Aux/IAA and ARF form homo- and hetero-oligomers for the transcriptional regulation, but what determines their association states is poorly understood. Here we report, to our knowledge, the first solution structure of domain III-IV of Aux/IAA17 (IAA17), and characterize molecular interactions underlying the homotypic and heterotypic oligomerization. The structure exhibits a compact β-grasp fold with a highly dynamic insert helix that is unique in Aux/IAA family proteins. IAA17 associates to form a heterogeneous ensemble of front-to-back oligomers in a concentration-dependent manner. IAA17 and ARF5 associate to form homo- or hetero-oligomers using a common scaffold and binding interfaces, but their affinities vary significantly. The equilibrium dissociation constants (KD) for homo-oligomerization are 6.6 μM and 0.87 μM for IAA17 and ARF5, respectively, whereas hetero-oligomerization reveals a ∼ 10- to ∼ 100-fold greater affinity (KD = 73 nM). Thus, individual homo-oligomers of IAA17 and ARF5 spontaneously exchange their subunits to form alternating hetero-oligomers for transcriptional repression. Oligomerization is mainly driven by electrostatic interactions, so that charge complementarity at the interface determines the binding affinity. Variable binding affinity by surface charge modulation may effectively regulate the complex interaction network between Aux/IAA and ARF family proteins required for the transcriptional control of auxin-response genes.
authors.affiliation: Department of Agricultural Biotechnology, College of Agriculture and Life Sciences, Seoul National University, Gwanak-gu, Seoul 151-921, Republic of Korea; and.
authors.forename: Mookyoung
authors.initials: M
authors.lastname: Han
authors.affiliation: Department of Agricultural Biotechnology, College of Agriculture and Life Sciences, Seoul National University, Gwanak-gu, Seoul 151-921, Republic of Korea; and.
authors.forename: Yangshin
authors.initials: Y
authors.lastname: Park
authors.affiliation: Department of Agricultural Biotechnology, College of Agriculture and Life Sciences, Seoul National University, Gwanak-gu, Seoul 151-921, Republic of Korea; and.
authors.forename: Iktae
authors.initials: I
authors.lastname: Kim
authors.affiliation: Division of Magnetic Resonance, Korea Basic Science Institute, Ochang, Chungbuk 363-883, Republic of Korea.
authors.forename: Eun-Hee
authors.initials: EH
authors.lastname: Kim
authors.affiliation: Department of Agricultural Biotechnology, College of Agriculture and Life Sciences, Seoul National University, Gwanak-gu, Seoul 151-921, Republic of Korea; and.
authors.forename: Tae-Kyung
authors.initials: TK
authors.lastname: Yu
authors.affiliation: Department of Agricultural Biotechnology, College of Agriculture and Life Sciences, Seoul National University, Gwanak-gu, Seoul 151-921, Republic of Korea; and jysuh@snu.ac.kr srheesnu@snu.ac.kr.
authors.forename: Sangkee
authors.initials: S
authors.lastname: Rhee
authors.affiliation: Department of Agricultural Biotechnology, College of Agriculture and Life Sciences, Seoul National University, Gwanak-gu, Seoul 151-921, Republic of Korea; and jysuh@snu.ac.kr srheesnu@snu.ac.kr.
authors.forename: Jeong-Yong
authors.initials: JY
authors.lastname: Suh
mesh_terms: D017360:Arabidopsis / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D019906:Nuclear Magnetic Resonance, Biomolecular; D009687:Nuclear Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D017510:Protein Folding; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D055672:Static Electricity; D013329:Structure-Activity Relationship; D014157:Transcription Factors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: C110728:AXR3 protein, Arabidopsis; D029681:Arabidopsis Proteins; D004268:DNA-Binding Proteins; C111371:MONOPTEROS protein, Arabidopsis; D009687:Nuclear Proteins; D014157:Transcription Factors
keywords: Aux/IAA; NMR spectroscopy; auxin; auxin response factor; protein structure