title: Identification of the roles of individual amino acid residues of the helix E of the major antenna of photosystem II (LHCII) by alanine scanning mutagenesis.
abstract: The functions of the helix E (W97-F105), an amphiphilic lumenal 310 helix of the major antenna of photosystem II (LHCII), are still unidentified. To elucidate the roles of individual amino acid residue of the helix E, alanine scanning mutagenesis has been performed to mutate every residue of this domain to alanine. The influence of every alanine substitution on the structure and function of LHCII has been investigated biochemically and spectroscopically. The results show that all mutations have little impact on the pigment binding and configuration. However, many mutants presented decreased thermo- or photo-stability compared with the wild type, highlighting the significance of this helix to the stability of LHCII. The most critical residue for stability is W97. The mutant W97A yielded very fragile trimeric pigment protein complexes. The structural analysis revealed that the hydrogen bonding and aromatic interactions between W97, F195, F194 and a water molecule contributed greatly to the stability of LHCII. Moreover, Q103A and F105A have been identified to be able to reinforce the tendency of aggregation in vitro. The structural analysis suggested that the enhancement in aggregation formation for Q103A and F105A might be attributed to the changing hydrophobicity of the region.
authors.affiliation: Key Laboratory of Photobiology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, P.R. China.
authors.forename: Cheng
authors.initials: C
authors.lastname: Liu
authors.affiliation: Key Laboratory of Photobiology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, P.R. China.
authors.forename: Yan
authors.initials: Y
authors.lastname: Rao
authors.affiliation: Key Laboratory of Photobiology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, P.R. China.
authors.forename: Lei
authors.initials: L
authors.lastname: Zhang
authors.affiliation: Key Laboratory of Photobiology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, P.R. China yangch@ibcas.ac.cn.
authors.forename: Chunhong
authors.initials: C
authors.lastname: Yang
mesh_terms: D000409:Alanine / Q000235:genetics* / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D045332:Photosystem II Protein Complex / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D017433:Protein Structure, Secondary
chemical_list: D045332:Photosystem II Protein Complex; D000409:Alanine
keywords: aggregation hydrophobicity; b complexes of photosystem II; light-harvesting chlorophyll a; photosynthesis; stability