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Publication Abstract from PubMed

The catalytic performance of the major CO2-assimilating enzyme, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), restricts photosynthetic productivity. Natural diversity in the catalytic properties of Rubisco indicates possibilities for improvement. Oceanic phytoplankton contain some of the most efficient Rubisco enzymes, and diatoms in particular are responsible for a significant proportion of total marine primary production as well as being a major source of CO2 sequestration in polar cold waters. Until now, the biochemical properties and three-dimensional structures of Rubisco from diatoms were unknown. Here, diatoms from Arctic waters were collected, cultivated and analyzed for their CO2 fixing capability. We characterized the kinetic properties of five, and determined the crystal structures of four Rubiscos selected for their high CO2-fixing efficiency. The DNA sequences of the rbcL and rbcS genes of the selected diatoms were similar, reflecting their close phylogenetic relationship. The Vmax and KM for the oxygenase and carboxylase activities at 25 degrees C and the specificity factors (Sc/o) at 15, 25 and 35 degrees C, were determined. The Sc/o values were high, approaching those of mono- and dicot plants, thus exhibiting good selectivity for CO2 relative to O2 Structurally, diatom Rubiscos belong to Form I C/D, containing small subunits characterised by a short betaA-betaB loop and a carboxy-terminal extension that forms a beta-hairpin structure (betaE-betaF loop). Of note, the diatom Rubiscos featured a number of posttranslational modifications of the large subunit, including 4-hydroxy-proline, betahydroxyleucine, hydroxylated, and nitrosylated cysteine, mono-, and di-hydroxylated lysine, and tri-methylated lysine. Our studies suggest adaptation toward achieving efficient CO2-fixation in Arctic diatom Rubiscos.

Structural and functional analyses of Rubisco from arctic diatom species reveal unusual posttranslational modifications.,Valegard K, Andralojc PJ, Haslam RP, Pearce FG, Eriksen GK, Madgwick PJ, Kristoffersen AK, van Lun M, Klein U, Eilertsen HC, Parry MAJ, Andersson I J Biol Chem. 2018 Jun 20. pii: RA118.003518. doi: 10.1074/jbc.RA118.003518. PMID:29925588^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.