Poster: Photosynthesis (carbon)
Abs #
232: Identification of an amino acid residue involved in the species specificity of Rubisco Activase
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Presenter: |
Li, Cishan , cishanli@uiuc.edu |
Authors | Li, Cishan (A) Portis, Archie R (A) (B) | | Affiliations: |
(A): University of Illinois at Urbana-Champaign, Department of Plant Biology
(B): USDA/ARS Photosynthesis Research Unit, Urbana,IL
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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.
