Biogenesis and Metabolic Maintenance of Rubisco

Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) mediates the fixation of atmospheric CO2 in photosynthesis by catalyzing the carboxylation of the 5-carbon sugar ribulose-1,5-bisphosphate (RuBP). Rubisco is a remarkably inefficient enzyme, fixing only 2-10 CO2 molecules per second. Efforts to increase crop yields by bioengineering Rubisco remain unsuccessful, owing in part to the complex cellular machinery required for Rubisco biogenesis and metabolic maintenance. The large subunit of Rubisco requires the chaperonin system for folding, and recent studies have shown that assembly of hexadecameric Rubisco is mediated by specific assembly chaperones. Moreover, Rubisco function can be inhibited by a range of sugar-phosphate ligands, including RuBP. Metabolic repair depends on remodeling of Rubisco by the ATP-dependent Rubisco activase and hydrolysis of inhibitory sugar phosphates by specific phosphatases. Here, we review our present understanding of the structure and function of these auxiliary factors and their utilization in efforts to engineer more catalytically efficient Rubisco enzyme

Sequence alignment of RbcX-II from green algae.

<p>Amino acid sequences of selected RbcX-II homologs from green algae, mosses and plants were aligned using Clustal-Ω. Note that for the green algae <i>Coccomyxa subellipsoidea</i>, <i>Chlorella variabilis</i>, <i>Volvox carteri</i>, <i>Ostreococcus tauri</i> and <i>Micromonas pusilla</i> only one RbcX-II sequence is shown. For comparison, RbcX-I from <i>A</i>. <i>thaliana</i>, <i>Synechococcus</i> sp. PCC7002 and <i>Anabaena sp</i>. CA are also aligned. All sequence numbering is based on the open reading frames. Secondary structure elements are indicated above the sequences. In the alignment, similar residues are shown in red and identical residues in white using bold lettering on red background. Blue frames indicate homologous regions. The consensus sequence is shown at the bottom. The forward arrow designates the beginning of the mature RbcX-II proteins. The diamond symbol at the end of the CrRbcX-IIb sequence indicates that the sequence continues with 130 amino acids not displayed. Asterisks denote residues known to be essential for RbcX function.</p