title: Structure of the catalytic domain of a state transition kinase homolog from Micromonas algae.
abstract: Under natural environments, plants and algae have evolved various photosynthetic acclimation mechanisms in response to the constantly changing light conditions. The state transition and long-term response processes in photosynthetic acclimation involve remodeling and composition alteration of thylakoid membrane. A chloroplast protein kinase named Stt7/STN7 has been found to have pivotal roles in both state transition and long-term response. Here we report the crystal structures of the kinase domain of a putative Stt7/STN7 homolog from Micromonas sp. RCC299 (MsStt7d) in the apo form and in complex with various nucleotide substrates. MsStt7d adopts a canonical protein kinase fold and contains all the essential residues at the active site. A novel hairpin motif, found to be a conserved feature of the Stt7/STN7 family and indispensable for the kinase stability, interacts with the activation loop and fixes it in an active conformation. We have also demonstrated that MsStt7d is a dualspecifi city kinase that phosphorylates both Thr and Tyr residues. Moreover, preliminary in vitro data suggest that it might be capable of phosphorylating a consensus N-terminal pentapeptide of light-harvesting proteins Micromonas Lhcp4 and Arabidopsis Lhcb1 directly. The potential peptide/protein substrate binding site is predicted based on the location of a pseudo-substrate contributed by the adjacent molecule within the crystallographic dimer. The structural and biochemical data presented here provide a framework for an improved understanding on the role of Stt7/STN7 in photosynthetic acclimation.
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.forename: Xuepeng
authors.initials: X
authors.lastname: Wei
authors.forename: Mei
authors.initials: M
authors.lastname: Li
authors.forename: Xiaowei
authors.initials: X
authors.lastname: Pan
authors.forename: Wenrui
authors.initials: W
authors.lastname: Chang
authors.forename: Zhenfeng
authors.initials: Z
authors.lastname: Liu
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D017360:Arabidopsis / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites; D020134:Catalytic Domain; D000460:Chlorophyta / Q000201:enzymology*; D018360:Crystallography, X-Ray; D051357:Cyclin-Dependent Kinase 2 / Q000737:chemistry / Q000378:metabolism; D008969:Molecular Sequence Data; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D017433:Protein Structure, Secondary; D016415:Sequence Alignment; D013379:Substrate Specificity
chemical_list: D029681:Arabidopsis Proteins; D017346:Protein Serine-Threonine Kinases; D051357:Cyclin-Dependent Kinase 2