Subjects: Biology >> Biophysics >> Biochemistry & Molecular Biology submitted time 2016-05-12
Fan, Minrui
Li, Mei
Liu, Zhenfeng
Cao, Peng
Pan, Xiaowei
Zhang, Hongmei
Zhao, Xuelin
Zhang, Jiping
Chang, Wenrui
Fan, Minrui
Abstract： The photosystem II protein PsbS has an essential role in qE-type nonphotochemical quenching, which protects plants from photodamage under excess light conditions. qE is initiated by activation of PsbS by low pH, but the mechanism of PsbS action remains elusive. Here we report the low-pH crystal structures of PsbS from spinach in its free form and in complex with the qE inhibitor N, N'-dicyclohexylcarbodiimide (DCCD), revealing that PsbS adopts a unique folding pattern, and, unlike other members of the light-harvesting-complex superfamily, it is a noncanonical pigment-binding protein. Structural and biochemical evidence shows that both active and inactive PsbS form homodimers in the thylakoid membranes, and DCCD binding disrupts the lumenal intermolecular hydrogen bonds of the active PsbS dimer. Activation of PsbS by low pH during qE may involve a conformational change associated with altered lumenal intermolecular interactions of the PsbS dimer.
Peer Review Status:
Awaiting Review
Subjects: Biology >> Biophysics >> Biochemistry & Molecular Biology submitted time 2016-05-11
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 Mn2+ (or Mg2+) 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.
Peer Review Status:Awaiting Review
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