Biochemical controls: how algae fix CO2 (Introduction)

by David Turell , Monday, March 04, 2024, 18:42 (55 days ago) @ David Turell

Mechanism described:

https://www.sciencedaily.com/releases/2024/03/240301134736.htm

"Plants and algae fix carbon through photosynthesis, which converts CO2 to organic carbon. This biological process is catalyzed by the Rubisco enzyme, the most abundant protein on Earth. In many algae, Rubisco is densely packed into a microcompartment called the pyrenoid, which plays an important role in the CO2 accumulation in aquatic environments. Notably, approximately one-third of global carbon fixation is estimated to occur within algal pyrenoids. Apart from Rubisco, the primary component of pyrenoids, the pyrenoid-associated proteins in most algae remain unclarified.

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"Interestingly, various pyrenoid-associated proteins have been reported among the algae studied to date, suggesting that CO2-fixing organelles evolved independently in each algal group.

"This is an example of convergent evolution at the molecular level.

From the original article: https://www.pnas.org/doi/10.1073/pnas.2318542121#supplementary-materials

"Abstract:
Pyrenoids are microcompartments that are universally found in the photosynthetic plastids of various eukaryotic algae. They contain ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and play a pivotal role in facilitating CO2 assimilation via CO2-concentrating mechanisms (CCMs). Recent investigations involving model algae have revealed that pyrenoid-associated proteins participate in pyrenoid biogenesis and CCMs. However, these organisms represent only a small part of algal lineages, which limits our comprehensive understanding of the diversity and evolution of pyrenoid-based CCMs. Here we report a pyrenoid proteome of the chlorarachniophyte alga Amorphochlora amoebiformis, which possesses complex plastids acquired through secondary endosymbiosis with green algae. Proteomic analysis using mass spectrometry resulted in the identification of 154 potential pyrenoid components. Subsequent localization experiments demonstrated the specific targeting of eight proteins to pyrenoids. These included a putative Rubisco-binding linker, carbonic anhydrase, membrane transporter, and uncharacterized GTPase proteins. Notably, most of these proteins were unique to this algal lineage. We suggest a plausible scenario in which pyrenoids in chlorarachniophytes have evolved independently, as their components are not inherited from green algal pyrenoids." (my bold)

Comment: no surprise pyrenoids ae so complex. More evidence for design. CO2 must be fixed to be chemically useful, just as Nitrogen gas must be fixed.