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

• Published in: Cell Vol. 171; no. 1; pp. 133 - 147.e14
• Main Authors: Mackinder, Luke C.M., Chen, Chris, Leib, Ryan D., Patena, Weronika, Blum, Sean R., Rodman, Matthew, Ramundo, Silvia, Adams, Christopher M., Jonikas, Martin C.
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 21.09.2017
• Subjects: affinity purification mass spectrometry; carbon fixation; CCM; Chlamydomonas reinhardtii; CO2-concentrating mechanism; high-throughput fluorescence protein tagging; photosynthesis; pyrenoid; Rubisco; CO2-concentrating mechanism; photosynthesis; Chlamydomonas reinhardtii; pyrenoid; Rubisco; affinity purification mass spectrometry; CCM; carbon fixation; high-throughput fluorescence protein tagging
• ISSN: 0092-8674; 1097-4172
• DOI: 10.1016/j.cell.2017.08.044

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 undescribed 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. [Display omitted] •Localizations and physical interactions of candidate CO2-concentrating mechanism (CCM) proteins were determined•The data reveal three previously undescribed pyrenoid layers and 89 pyrenoid proteins•Plasma membrane inorganic carbon transporters LCI1 and HLA3 form a complex•Carbonic anhydrase 6 localizes to the flagella, changing the model of the CCM Microscopy and proteomic analyses reveal three previously unknown layers of the pyrenoid, the cellular organelle in algae responsible for one-third of global CO2 fixation