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Title: DIFFERENTIAL EFFECT OF N AND C TERMINAL DELETIONS ON THE TWO ACTIVITIES OF RUBISCO ACTIVASE

Author
item ESAU, BRIAN - UNIV OF ILLINOIS
item Snyder Jr, Gordon
item PORTIS JR, ARCHIE

Submitted to: Archives of Biochemistry and Biophysics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: Rubisco is the first enzyme in photosynthesis, the process by which plants use light energy from the sun to make carbohydrates from carbon dioxide and water. The activity of this enzyme is regulated by the activity of another protein called Rubisco activase. Only very limited information is available on the structure of this protein and how it functions to change the activity of Rubsico. In this study, we obtained new information on two important areas in the sequence of the protein by determining the effect of the enzyme in limiting photosynthetic performance and how it may be altered.

Technical Abstract: Spinach (Spinacea oleracea) ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activase was subjected to partial proteolysis with trypsin and directed deletions were made by modifying the spinach Rubisco activase cDNA and expressing the protein in Escherichia coli. Protein exposed to trypsin displayed a more rapid loss of the ability to promote the activation of decarbamylated Rubisco than ATP hydrolysis (e.g. 10 percent and 50 percent activity remaining respectively). A series of N-terminal deletions exhibited an abolition of Rubisco activation after the twelfth residue, a conserved tryptophan, was deleted. Conversely, a deletion of 19 residues at the C-terminus increased Rubisco activation with little effect on ATP hydrolysis resulting in an increased efficiency of activation. The C-terminal deletion mutant was further modified by a site-directed mutation in the ATP binding region which was previously observed to increase the efficiency of activation (J.B. Shen and W. L. Ogren (1991) Plant Physiol. 99,102-1207). The efficiency of activation with this double mutant was greater than that for either of the mutants alone. The results indicate that a conserved tryptophan in the N- terminal portion of Rubisco activase is critical for promotion of the activation of Rubisco, consistent with a possible role in interaction with Rubisco. The C-terminus appears to have a regulatory effect on both Rubisco activation and ATP hydrolysis.