Sigal Lechno-Yossef

  • Feb 26, 2018

Date & Location: February 26, 2018, at 4p; Room 101 Biochemistry Building

Subject: Characterization of cyanobacterial RubisCO activase in Fremyella diplosiphon

About the Speaker

University: Michigan State University

Seminar Summary: Ribulose bisphosphate Carboxylase/Oxygenase (RubisCO) is a major enzyme responsible for primary productivity on earth. It catalyzes the first step in photosynthetic assimilation of CO2 in plants, cyanobacteria and photosynthetic bacteria.  RubisCO performs two competing reactions, carboxylation, which results in carbon assimilation and sugar formation, and oxygenation, which leads to photorespiration. Additionally, in plants, RubisCO might be inhibited by different sugar phosphate molecules, such as the substrate Ribulose 1,5 bisphosphate (RuBP). Removal of the inhibitory sugar is required for activation of the enzyme and is carried out by the enzyme RubisCO activase (Rca). RubisCO activase is an ATPase associated with various cellular activities (AAA+) protein. Plant Rca is the subject of intensive research because it is believed that it is involved in modulation of the thermotolerance of photosynthesis and coordinating the rate of light reaction and carbon fixation.

In cyanobacteria, RubisCO is segregated into a specialized organelle called the carboxysome. The carboxysome allows localized increased concentrations of the RubisCO, as well as increased CO2 concentrations, and lower O2 concentrations. This results in increased carboxylation reaction and decreased photorespiration.  The requirement for RubisCO activation in cyanobacteria has not been established. With the increase in available cyanobacterial genomes in the databases, it became clear that many genomes of beta-cyanobacteria contain a gene for Rca. Very little is known about this gene product, its regulation or function in cyanobacteria. By gene deletion, over-expression and fluorescent labeling, we are investigating the role and cellular localization of Rca in the model cyanobacterium Fremyella diplosiphon. F. diplosiphon undergoes complementary chromatic acclimation (CCA). Although the main effect of CCA is altering the phycobilin composition in the photosynthetic antenna, some effects on carboxysome number and size have been observed during the process. We show a connection between the CCA and Rca in this organism.