Editing Pyrenoid (section)

=== Molecular components ===

In ''Chlamydomonas'', specifically the model alga ''[[Chlamydomonas reinhardtii]]'':
* Mutagenic work has shown that the RuBisCO small subunit is important for pyrenoid matrix assembly,<ref>Genkov, T., Meyer, M., Griffiths, H., & Spreitzer, R. J. (2010). Functional hybrid rubisco enzymes with plant small subunits and algal large subunits engineered ''RBCS'' cDNA for expression in ''Chlamydomonas''. ''Journal of Biological Chemistry'',285(26), 19833-19841 {{PMID|20424165}}</ref> and that two solvent exposed alpha-helices of the RuBisCO small subunit are key to the process.<ref>Meyer, M. T., Genkov, T., Skepper, J. N., Jouhet, J., Mitchell, M. C., Spreitzer, R. J., & Griffiths, H. (2012). RuBisCO small-subunit α-helices control pyrenoid formation in ''Chlamydomonas''. ''Proceedings of the National Academy of Sciences'', 109(47), 19474-19479. {{PMID|23112177}}</ref>
* Assembly of RuBisCO into a pyrenoid was shown to require the intrinsically disordered RuBisCO-binding repeat protein EPYC1, which was proposed to "link" multiple RuBisCO holoenzymes together to form the pyrenoid matrix.<ref>{{Cite journal|last1=Mackinder|first1=Luke C. M.|last2=Meyer|first2=Moritz T.|last3=Mettler-Altmann|first3=Tabea|last4=Chen|first4=Vivian K.|last5=Mitchell|first5=Madeline C.|last6=Caspari|first6=Oliver|last7=Rosenzweig|first7=Elizabeth S. Freeman|last8=Pallesen|first8=Leif|last9=Reeves|first9=Gregory|last10=Itakura|first10=Alan|last11=Roth|first11=Robyn|last12=Sommer|first12=Frederik|last13=Geimer|first13=Stefan|last14=Mühlhaus|first14=Timo|last15=Schroda|first15=Michael|last16=Goodenough|first16=Ursula|last17=Stitt|first17=Mark|last18=Griffiths|first18=Howard|last19=Martin C.|first19=Jonikas|date=2016-05-24|title=A repeat protein links Rubisco to form the eukaryotic carbon-concentrating organelle|journal=Proceedings of the National Academy of Sciences|language=en|volume=113|issue=21|pages=5958–5963|doi=10.1073/pnas.1522866113|issn=0027-8424|pmc=4889370|pmid=27166422|doi-access=free|bibcode=2016PNAS..113.5958M }}</ref> EPYC1 and Rubisco together were shown to be sufficient to reconstitute phase-separated droplets that show similar properties to ''C. reinhardtii'' pyrenoids in vivo, further supporting a "linker" role for EPYC1.<ref>{{Cite journal|last1=Wunder|first1=Tobias|last2=Cheng|first2=Steven Le Hung|last3=Lai|first3=Soak-Kuan|last4=Li|first4=Hoi-Yeung|last5=Mueller-Cajar|first5=Oliver|date=2018-11-29|title=The phase separation underlying the pyrenoid-based microalgal Rubisco supercharger|url=https://www.nature.com/articles/s41467-018-07624-w|journal=Nature Communications|language=en|volume=9|issue=1|pages=5076|doi=10.1038/s41467-018-07624-w|issn=2041-1723|pmc=6265248|pmid=30498228|bibcode=2018NatCo...9.5076W}}</ref>
* SAGA1 and MITH1 are each necessary for the appearance of matrix-traversing membranes in the pyrenoid; combined they are sufficient for such membranes to appear, even when introduced into the model "higher" land plant ''[[Arabidopsis thaliana]]''. Without those matrix-traversing membrane "tubules", there would be no way for {{CO2}} to enter the pyrenoid.<ref>{{cite journal |last1=Hennacy |first1=Jessica H. |last2=Atkinson |first2=Nicky |last3=Kayser-Browne |first3=Angelo |last4=Ergun |first4=Sabrina L. |last5=Franklin |first5=Eric |last6=Wang |first6=Lianyong |last7=Eicke |first7=Simona |last8=Kazachkova |first8=Yana |last9=Kafri |first9=Moshe |last10=Fauser |first10=Friedrich |last11=Vilarrasa-Blasi |first11=Josep |last12=Jinkerson |first12=Robert E. |last13=Zeeman |first13=Samuel C. |last14=McCormick |first14=Alistair J. |last15=Jonikas |first15=Martin C. |title=SAGA1 and MITH1 produce matrix-traversing membranes in the CO2-fixing pyrenoid |journal=Nature Plants |date=15 November 2024 |doi=10.1038/s41477-024-01847-0 |doi-access=free|pmc=11649565}}</ref>

The proteome of the ''Chlamydomonas'' pyrenoid has been characterized,<ref>{{Cite journal|last1=Zhan|first1=Yu|last2=Marchand|first2=Christophe H.|last3=Maes|first3=Alexandre|last4=Mauries|first4=Adeline|last5=Sun|first5=Yi|last6=Dhaliwal|first6=James S.|last7=Uniacke|first7=James|last8=Arragain|first8=Simon|last9=Jiang|first9=Heng|last10=Gold|first10=Nicholas D.|last11=Martin|first11=Vincent J. J.|date=2018-02-26|title=Pyrenoid functions revealed by proteomics in Chlamydomonas reinhardtii|journal=PLOS ONE|language=en|volume=13|issue=2|pages=e0185039|doi=10.1371/journal.pone.0185039|issn=1932-6203|pmc=5826530|pmid=29481573|doi-access=free|bibcode=2018PLoSO..1385039Z }}</ref> and the localizations and protein-protein interactions of dozens of pyrenoid-associated proteins were systematically determined.<ref>{{Cite journal|last1=Mackinder|first1=Luke C. M.|last2=Chen|first2=Chris|last3=Leib|first3=Ryan D.|last4=Patena|first4=Weronika|last5=Blum|first5=Sean R.|last6=Rodman|first6=Matthew|last7=Ramundo|first7=Silvia|last8=Adams|first8=Christopher M.|last9=Jonikas|first9=Martin C.|date=2017-09-21|title=A Spatial Interactome Reveals the Protein Organization of the Algal CO2-Concentrating Mechanism|journal=Cell|language=English|volume=171|issue=1|pages=133–147.e14|doi=10.1016/j.cell.2017.08.044|issn=0092-8674|pmid=28938113|pmc=5616186|doi-access=free}}</ref> Proteins localized to the pyrenoid include RuBisCO activase,<ref>McKay, R. M. L., Gibbs, S. P., & Vaughn, K. C. (1991). RuBisCo activase is present in the pyrenoid of green algae. Protoplasma, 162(1), 38-45.</ref> nitrate reductase<ref>Lopez-Ruiz, A., Verbelen, J. P., Roldan, J. M., & Diez, J. (1985). Nitrate reductase of green algae is located in the pyrenoid. ''Plant Physiology'', 79(4), 1006-1010.</ref> and nitrite reductase.<ref>López-Ruiz, A., Verbelen, J. P., Bocanegra, J. A., & Diez, J. (1991). Immunocytochemical localization of nitrite reductase in green algae. ''Plant Physiology'', 96(3), 699-704.</ref>

In ''Chlamydomonas'', a high-molecular weight complex of two proteins (LCIB/LCIC) forms an additional concentric layer around the pyrenoid, outside the starch sheath, and this is currently hypothesised to act as a barrier to CO<sub>2</sub>-leakage or to recapture CO<sub>2</sub> that escapes from the pyrenoid.<ref>Yamano, T., Tsujikawa, T., Hatano, K., Ozawa, S. I., Takahashi, Y., & Fukuzawa, H. (2010). Light and low-CO<sub>2</sub>-dependent LCIB–LCIC complex localization in the chloroplast supports the carbon-concentrating mechanism in ''Chlamydomonas reinhardtii''. Plant and Cell Physiology, 51(9), 1453-1468.{{PMID|20660228}}</ref>