title: Structural Mechanism Underlying the Specific Recognition between the Arabidopsis State-Transition Phosphatase TAP38/PPH1 and Phosphorylated Light-Harvesting Complex Protein Lhcb1.
abstract: During state transitions, plants regulate energy distribution between photosystems I and II through reversible phosphorylation and lateral migration of the major light-harvesting complex LHCII. Dephosphorylation of LHCII and the transition from state 2 to state 1 requires a thylakoid membrane-associated phosphatase named TAP38 or PPH1. TAP38/PPH1 specifically targets LHCII but not the core subunits of photosystem II, whereas the underlying molecular mechanism of their mutual recognition is currently unclear. Here, we present the structures of Arabidopsis thaliana TAP38/PPH1 in the substrate-free and substrate-bound states. The protein contains a type 2C serine/threonine protein phosphatase (PP2C) core domain, a Mn(2+) (or Mg(2+)) binuclear center and two additional motifs contributing to substrate recognition. A 15-mer phosphorylated N-terminal peptide of Lhcb1 binds to TAP38/PPH1 on two surface clefts enclosed by the additional motifs. The first segment of the phosphopeptide is clamped by a pair of tooth-like arginine residues at Cleft 1 site. The binding adopts the lock-and-key mechanism with slight rearrangement of the substrate binding residues on TAP38/PPH1. Meanwhile, a more evident substrate-induced fitting occurs on Cleft 2 harboring the extended part of the phosphopeptide. The results unravel the bases for the specific recognition between TAP38/PPH1 and phosphorylated Lhcb1, a crucial step in state transitions.
authors.affiliation: National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China School of Life Sciences, University of Chinese Academy of Sciences, Beijing100101, China.
authors.forename: Xuepeng
authors.initials: X
authors.lastname: Wei
authors.affiliation: National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China.
authors.forename: Jiangtao
authors.initials: J
authors.lastname: Guo
authors.affiliation: National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China.
authors.forename: Mei
authors.initials: M
authors.lastname: Li
authors.affiliation: National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China liuzf@sun5.ibp.ac.cn.
authors.forename: Zhenfeng
authors.identifier: http://orcid.org/0000-0001-5502-9474
authors.initials: Z
authors.lastname: Liu
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D010749:Phosphoprotein Phosphatases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary
chemical_list: D029681:Arabidopsis Proteins; C423618:CAB2 protein, Arabidopsis; D045342:Light-Harvesting Protein Complexes; D010749:Phosphoprotein Phosphatases; C550563:TAP38 protein, Arabidopsis