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Title: ACTIVASE REGION ON CHLOROPLAST RIBULOSE-1,5BISPHOSPHATE CARBOXYLASE/OXYGENASE NONCONSERVATIVE SUBSITUTION IN THE LARGE SUBUNIT ALTEALTERS SPECUES SPECIFICITY OF PROTEIN INTERATIONS

Author
item OTT, CAROLYN - BIOCHEMISTRY UNIV OF NEB
item SMITH, BRYAN - BIOCHEMISTRY UNIF OF NEB
item Portis Jr, Archie
item SPREITZER, ROBERT - BIOCHEMISTRY UNIV OF NEB

Submitted to: Journal of Biological Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/16/2000
Publication Date: 6/16/2000
Citation: Ott, C.M., Smith, B.D., Portis Jr, A.R., Spreitzer, R.J. 2000. Activase region on chloroplast ribulose-1,5bisphosphate carboxylase/oxygenase nonconservative subsitution in the large subunit altealters specues specificity of protein interactions. Journal of Biological Chemistry. 275:26241-26244.

Interpretive Summary: The activity of Rubisco, the enzyme that captures carbon dioxide, often limits photosynthesis, the process by which plants use light energy from the sun to make carbohydrates for growth from carbon dioxide and water. In order to have activity, Rubisco requires modification by a process called activation, which is determined and hence regulated by another protein known as Rubisco activase. Rubisco activity might be increased to improve plant growth by altering the regulation of activation. Activation by Rubisco activase involves binding of the proteins to each other because the proteins from one species of plants, the Solanaceae, do not work in combination with either protein from other species. The Rubisco protein in these plants has several unique amino acid differences located on its surface that may determine the nature of the interaction with Rubisco activase. Past work identified one amino acid in this region that could be changed and was sufficient to allow Rubisco from a non-Solanceous species to be activated by a Solanceous Rubisco activase, but not by the non-Solanaceous protein that worked before this change. In this work additional substitutions were made in this area to further delimit the size and required characteristics of the binding region. This information will benefit scientists attempting to modify the properties and regulation of Rubisco in ways beneficial for increased photosynthesis by crop plants.

Technical Abstract: The activation of Rubisco by removing phosphorylated inhibitors from the Rubisco active site. Activase from Solanaceae plants (such as tobacco) fail to activate Rubisco from non-Solanaceae plants (including spinach and Chlamydomonas reinhardtii), and non-Solanaceae activase fails to activate Solanaceae Rubisco. Directed mutagenesis and chloroplast transformation previously showed that a proline-89 to arginine substitution on the surface of the large subunit of Chlamydomonas Rubisco switched its specificity from non-Solanaceae to Solanaceae activase activation. To delimit the size of this putative activase binding region, substitutions were created at positions that flank residue 89. As in the past, these substitutions changed the identities of Chlamydomonas residues to those of tobacco. Whereas an aspartate-86 to arginine substitution had little effect, aspartate-94 to lysine Rubisco was only partially activated by spinach activase but now fully activated by tobacco activase. In an attempt to eliminate the activase/Rubisco interaction, proline-89 was changed to alanine, which is not present in either non-Solanaceae or Solanaceae Rubisco. However, this substitution also caused a reversal of activase specificity. These results indicate that amino-acid identity alone does not determine activase specificity.