Sigal Lechno-Yossef

  • Oct 9, 2018

Date & Location: October 9, 2018, at 12p; Room 168 Plant Biology Building

Subject: RubisCO activase-like protein in the cyanobacterium Fremyella diplosiphon

Abstract: The highly abundant protein Ribulose bisphosphate Carboxylase/Oxygenase (RubisCO) is the key enzyme of global carbon fixation. RubisCO is inhibited by various sugar phosphate molecules, the removal of which requires the chaperone RubisCO activase. Cyanobacterial RubisCO is segregated in proteinaceous organelles, carboxysomes. It exhibits different catalytic properties than plant RubisCO and has been reported to be less sensitive to inhibition. This latter observation led to the wide-spread impression that most cyanobacteria other than the heterocyst-forming do not employ a RubisCO activase.

Here, we report the presence of a widespread Activase-Like Cyanobacterial protein (ALC), which exhibits the hallmark sequence features of plant RubisCO activase, with the distinctive fusion of a C-terminal domain that resembles the small-subunit of RubisCO (SSLD). Notably, we find a general correlation between the phylogenies of ALCs and the large subunit of RubisCO (RbcL) for cyanobacterial species, which suggests co-evolution of these proteins. We show that the ALC in the freshwater model cyanobacterium Fremyella diplosiphon (FdALC) localizes to carboxysomes and shows ATPase activity. Moreover, although a Δalc deletion mutant does not exhibit an obvious growth phenotype under various experimental growth conditions, there is a strong ultrastructural phenotype in enriched CO2 that is consistent with an increased stress response and impaired regulation of carboxysome biogenesis. The finding of the ALC in the vicinity of RubisCO in the carboxysome, the presence of an SSLD, and structural modeling collectively suggest that the ALC interacts with RubisCO potentially to regulate its activity in many cyanobacteria.

Speaker Lab: Dr. Cheryl Kerfeld