Identification of a carbonic anhydrase–Rubisco complex within the alpha-carboxysome

Journal Article · Fri Oct 20 00:00:00 EDT 2023 · Proceedings of the National Academy of Sciences of the United States of America

DOI:https://doi.org/10.1073/pnas.2308600120· OSTI ID:2203163

Blikstad, Cecilia  ^[1]; Dugan, Eli J.  ^[2]; Laughlin, Thomas G.  ^[2]; Turnšek, Julia B.  ^[2]; Liu, Mira D.  ^[3]; Shoemaker, Sophie R.  ^[2]; Vogiatzi, Nikoleta  ^[4]; Remis, Jonathan P.  ^[5]; Savage, David F.  ^[6]

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1. Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720, Department of Chemistry - Ångström Laboratory, Uppsala University, Uppsala 75120, Sweden
2. Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720
3. Department of Chemistry, University of California, Berkeley, CA 94720
4. Department of Chemistry - Ångström Laboratory, Uppsala University, Uppsala 75120, Sweden
5. California Institute for Quantitative Biosciences, University of California, Berkeley, CA 94720
6. Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720, HHMI, University of California, Berkeley, CA 94720

Carboxysomes are proteinaceous organelles that encapsulate key enzymes of CO ₂ fixation—Rubisco and carbonic anhydrase—and are the centerpiece of the bacterial CO ₂ concentrating mechanism (CCM). In the CCM, actively accumulated cytosolic bicarbonate diffuses into the carboxysome and is converted to CO ₂ by carbonic anhydrase, producing a high CO ₂ concentration near Rubisco and ensuring efficient carboxylation. Self-assembly of the α-carboxysome is orchestrated by the intrinsically disordered scaffolding protein, CsoS2, which interacts with both Rubisco and carboxysomal shell proteins, but it is unknown how the carbonic anhydrase, CsoSCA, is incorporated into the α-carboxysome. Here, we present the structural basis of carbonic anhydrase encapsulation into α-carboxysomes from Halothiobacillus neapolitanus . We find that CsoSCA interacts directly with Rubisco via an intrinsically disordered N-terminal domain. A 1.98 Å single-particle cryoelectron microscopy structure of Rubisco in complex with this peptide reveals that CsoSCA binding is predominantly mediated by a network of hydrogen bonds. CsoSCA's binding site overlaps with that of CsoS2, but the two proteins utilize substantially different motifs and modes of binding, revealing a plasticity of the Rubisco binding site. Our results advance the understanding of carboxysome biogenesis and highlight the importance of Rubisco, not only as an enzyme but also as a central hub for mediating assembly through protein interactions.

• Sponsoring Organization: USDOE
• Grant/Contract Number: SC00016240
• OSTI ID: 2203163
• Journal Information: Proceedings of the National Academy of Sciences of the United States of America, Journal Name: Proceedings of the National Academy of Sciences of the United States of America Vol. 120 Journal Issue: 43; ISSN 0027-8424
• Publisher: Proceedings of the National Academy of Sciences
• Country of Publication: United States
• Language: English