Cell
Volume 171, Issue 1, 21 September 2017, Pages 133-147.e14
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Article
A Spatial Interactome Reveals the Protein Organization of the Algal CO2-Concentrating Mechanism

https://doi.org/10.1016/j.cell.2017.08.044Get rights and content
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Highlights

  • 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

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 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.

Keywords

CO2-concentrating mechanism
CCM
carbon fixation
Chlamydomonas reinhardtii
photosynthesis
pyrenoid
Rubisco
high-throughput fluorescence protein tagging
affinity purification mass spectrometry

Cited by (0)

6

Present address: Department of Biology, University of York, York YO10 5DD, UK

7

Present address: Department of Biomolecular Engineering, UC Santa Cruz, Santa Cruz, CA 95064, USA

8

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