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Title: IDENTIFICATION OF AN AMINO ACID RESIDUE INVOLVED IN THE SPECIES SPECIFICITY OF RUBISCO ACTIVASE

Author
item LI, CISHAN - UNIVERSITY OF ILLINOIS
item PORTIS JR, ARCHIE

Submitted to: American Society of Plant Biologists Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 3/15/2004
Publication Date: 7/26/2004
Citation: Li, C., Portis Jr, A.R. 2004. Identification of an amino acid residue involved in the species specificity of Rubisco activase [abstract]. American Society of Plant Biologists Annual Meeting. Available: http://abstracts.aspb.org/pb2004/public/P40/7257.html.

Interpretive Summary:

Technical Abstract: Rubisco activase (RA) is a nuclear-encoded, ATP-dependent chloroplast protein which activates Rubisco by releasing the sugar phosphate inhibitors (e.g. RuBP) that tightly bind to it. The interaction of Rubisco-RuBP (ER) and RA is species dependent between Solanaceae (e.g. tobacco, tomato) and non-Solanaceae species (e.g. spinach, barley). To understand this phenomenon, we constructed two chimeric activases by replacing a region close to Carboxyl-terminus of spinach (Spinacea oleracea) small isoform activase with the homologous sequence from tobacco (Nicotiana tabacum) activase and vice-versa. The spinach chimeric activase (SCA) showed much lower ATPase activity as compared to WT activase and could activate neither spinach ER nor tobacco ER. In contrast the tobacco chimeric activase (TCA) showed similar ATPase activity and exhibited an activation pattern that was similar to spinach activase: it activated spinach ER far better than tobacco ER. Protein sequence comparison in the region revealed that five amino acids (269, 302/303, 308 and 311) in mature spinach activase were distinct from the tobacco activase homolog. By mutating these five residues in TCA back to the corresponding residues in tobacco activase, we observed that one amino acid mutation (K311D) abolished TCA's preference to better activate spinach ER while all the other mutations showed the same activation pattern as TCA. We conclude that Lys311 in TCA is critical for its ability to better activate spinach ER. We speculate that this residue might also be involved in the species-dependent characteristics of the native activases and we are further investigating the role of this amino acid by site-directed mutagenesis.