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Title: CONFORMATIONAL AND FUNCTIONAL DETAILS OF CARBOXYL-TERMINAL DOMAIN OF THE 46-KDA ISOFORM OF ARABIDOPSIS RUBISCO ACTIVASE

Author
item WANG, DAFU - UNIVERSITY OF ILLINOIS
item Portis Jr, Archie

Submitted to: Plant Biology Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 2/28/2005
Publication Date: 7/16/2005
Citation: Wang, D., Portis Jr, A.R. 2005. Conformational and functional details of carboxyl-terminal domain of the 46-kda isoform of arabidopsis rubisco activase [abstract]. Plant Biology Annual Meeting. Paper No. 267. Available: http://abstracts.aspb.org/pb2005/public/P43/7154.html.

Interpretive Summary:

Technical Abstract: In Arabidopsis, the larger (46-kDa) activase is involved in both redox regulation by thioredoxin-f at physiological ADP/ATP ratios and the down-regulation of Rubisco at limiting light intensities. A hypothetical model for the interactions between the C-terminal domain and the active sites of activase associated with redox regulation has been proposed (Zhang et al, 2001). Here we provided new biochemical evidences to uncover the conformational and functional details of the C-terminal domain. Mixing experiments using a GST fusion protein, cross-linking and gel-filtration experiments support the existence of a hetero-oligomerized complex of the smaller and larger isoforms. Limited proteolysis and immunoassay with a C-terminus specific antibody revealed a conformational change of the C-terminal domain after redox treatments. This conformational change could be a fundamental process in its regulatory role. We have previously reported that site-directed mutagenesis of C-terminal negatively charged residues altered the sensitivity to ADP inhibition, possibly by electrostatic interactions with positively charged residues near the nucleotide binding sites or other active sites. This hypothesis is further supported by two observations that 1) the reduced 46-kDa activase showed a higher affinity for ATP/Mg2+ than the oxidized form; 2) the 43-kDa isoform was less sensitive than the 46-kDa isoform to the inhibition of ATP hydrolysis by an amine-specific modifier. Several positively charged residues have been reported to be critical in the activities of Rubisco activase. Identification of the modified residues on activase will provide additional evidence on the interactions between the C-terminal domain and the active sites of Rubisco activase.