InterPro domain: IPR036385

RuBisCO (ribulose-1,5-bisphosphate carboxylase/oxygenase) is a bifunctional enzyme that catalyses both the carboxylation and oxygenation of ribulose-1,5-bisphosphate (RuBP), thus fixing carbon dioxide as the first step of the Calvin cycle. RuBisCO is the major protein in the stroma of chloroplasts, and in higher plants exists as a complex of 8 large and 8 small subunits. The small subunits induce conformational changes in the large subunits enhancing its catalytic rate. Studies in Oryza sativa demonstrate that the availability of the small subunit upregulates the transcript levels of the large subunit [ 1 ]. While the large subunit is coded for by a single gene, the small subunit is coded for by several different genes, which are distributed in a tissue specific manner. They are transcriptionally regulated by light receptor phytochrome [ 2 ], which results in RuBisCO being more abundant during the day when it is required.

The RuBisCo small subunit consists of a central four-stranded beta-sheet, with two helices packed against it [ 3 ].

1. Availability of Rubisco small subunit up-regulates the transcript levels of large subunit for stoichiometric assembly of its holoenzyme in rice. Plant Physiol. 160, 533-40
2. The genes encoding the small subunit of ribulose-1,5-bisphosphate carboxylase are expressed differentially in petunia leaves. Nucleic Acids Res. 14, 3325-42
3. Crystal structure of the unactivated form of ribulose-1,5-bisphosphate carboxylase/oxygenase from tobacco refined at 2.0-A resolution. J. Biol. Chem. 267, 16980-9