|Esquivel, Maria - UNIV OF LISBON PORTUGAL|
|Spreitzer, Robert - UNIV OF NE LINCOLN NE|
Submitted to: American Society of Plant Biologists Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: July 26, 2006
Publication Date: August 5, 2006
Citation: Esquivel, M.G., Spreitzer, R.J., Salvucci, M.E. 2006. Inter- and intramolecular subunit interactions of rubisco and activase. American Society of Plant Biologists Annual Meeting. P14001. Available: http://abstracts.aspb.org/ph2006/public/cgi-bin/search.cgi. Technical Abstract: Rubisco activase functions as a molecular chaperone, physically interacting with Rubisco to maintain the enzyme in a conformation competent for CO2 fixation. This action of activase is essential for photosynthesis and is the first reaction of photosynthesis disrupted by moderate heat stress. Directed mutagenesis studies with both activase and Rubisco have identified residues 94 and 89 of the Rubisco large subunit and 311 and 314 of activase as potential sites of interaction between Rubisco and activase (Li et al. 2005). To elucidate further details of the interaction, we have mutated Asp-94 of the Chlamydomonas Rubisco large subunit and Lys-311 of spinach activase to Cys in an attempt to stabilize the binary complex of Rubisco and activase using homobifunctional crosslinking reagents. In related studies, we are conducting activation assays with Rubisco enzymes that have mutations in small-subunit residues that affect CO2/O2 specificity and/or structural conformational. The results of these studies should show how constraints on the conformational flexibility of Rubisco affect activase function and Rubisco catalysis. Finally, we have examined subunit interactions between the 46 kDa redox-regulated alpha and the 42 kDa non-redox regulated beta forms of activase using an affinity tagged beta form. The results show that activase subunits self-associate spontaneously, exhibiting no specific requirement for metal cofactor or nucleotide. Together, the results provide new insights into the structure and function of the activase-Rubisco interaction.