A Spatial Interactome Reveals the Protein Organization of the Algal CO2-Concentrating Mechanism

Abstract

SUMMARY Approximately one-third of global CO2 fixation is performed by eukaryotic algae. Nearly all algae enhance their carbon assimilation by operating a CO2-concentrating mechanism (CCM) built around an organelle called the pyrenoid, whose protein composition is largely unknown. Here, we developed tools in the model alga Chlamydomonas reinhardtii to determine the localizations of 135 candidate CCM proteins, and physical interactors of 38 of these proteins. Our data reveal the identity of 89 pyrenoid proteins, including Rubisco-interacting proteins, photosystem I assembly factor candidates and inorganic carbon flux components. We identify three previously un-described protein layers of the pyrenoid: a plate-like layer, a mesh layer and a punctate layer. We find that the carbonic anhydrase CAH6 is in the flagella, not in the stroma that surrounds the pyrenoid as in current models. These results provide an overview of proteins operating in the eukaryotic algal CCM, a key process that drives global carbon fixation.

Light‐dependent N‐terminal phosphorylation of LHCSR3 and LHCB4 are interlinked in Chlamydomonas reinhardtii

“…Two further low CO 2 ‐inducible proteins (LCIB, LCIC) are present in the same cluster. Recent studies revealed that LCIB and LCIC interact with each other and presumably form a chloroplast‐localized complex (Mackinder et al ., ). In addition, several proteins related to general or oxidative stress can be observed in the LHCSR3‐CRX and FNR clusters (ClpB, BIP1, PRX4, HSP70B, HSP70C, HSP90B).…”

The singular properties of photosynthetic cytochrome c550 from the diatom Phaeodactylum tricornutum suggest new alternative functions

“…In addition, PSII activity has been initially described to be restricted to stromal thylakoids (McKay and Gibbs ). However, very recently, the presence of both intrinsic and extrinsic PSII subunits in the pyrenoid of the green alga C. reinhardtii has been reported (Mackinder et al , Zhan et al ), including the localization of the PsbQ extrinsic component of PSII in intrapyrenoid thylakoids (Mackinder et al ). Thus, the presence of the PSII extrinsic PSBV subunit (Cc 550 ) in this compartment could not be totally unexpected.…”

“…Components of the photosystem I (PSI) complex have also been found in pyrenoids, indicating that intrapyrenoid thylakoids could supply ATP to this compartment via cyclic electron transport, thus covering the energetic demands of carbon fixation at the same time as avoiding the evolution of inhibitory O 2 (McKay and Gibbs , Meyer and Griffiths ). Consequently, it was generally accepted that intrapyrenoid thylakoids are enriched in PSI and lack PSII, although in the green alga Chlamydomonas reinhardtii , the presence of PSII components has been recently reported (Mackinder et al ). However, the presence in this space of either the soluble photosynthetic cytochrome c 6 (Cc 6 ) or the Cc 550 , has not been yet addressed.…”

Conversion of NaHCO3 to Na2CO3 with a growth of Arthrospira platensis cells in 660 m2 raceway ponds with a CO2 bicarbonation absorber

“…Therefore, reducing CO 2 flue gas emissions to control global warming is a crucial task (Zhou et al, 2018). Microalgae contributes to approximately one-third of the global CO 2 fixation because of their substantial growth rate (Mackinder et al, 2017;Rosenzweig et al, 2017). Using CO 2 from flue gases as a carbon source to cultivate microalgae is one alternative method for reducing flue gas emissions.…”

“…In the first process, HCO À 3 sequentially passes through the plasma membrane, the chloroplast envelope and then the thylakoid membrane, finally arriving at the thylakoid lumen where it is catalysed to CO 2 . CO 2 is next fixed by the RubisCO enzyme (Amc et al, 2017) and then channelled into the Calvin cycle (Spalding, 2008;Mackinder et al, 2017;Hwangbo et al, 2018). In the second process, HCO À 3 in the periplasmic space is converted by carbonic anhydrase into CO 2 , which then diffuses to the stroma and is captured by RubisCO.…”