9ly8

Structural highlights

Function

CSOSA_HALNC The major shell protein of the carboxysome, a polyhedral inclusion where RuBisCO (ribulose bisphosphate carboxylase, ccbL-ccbS) is sequestered (PubMed:16535117, PubMed:7934888). Assembles into hexamers which make sheets that form the facets of the polyhedral carboxysome (PubMed:17518518). The shell probably limits the diffusion of CO(2) into and out of the carboxysome (Probable). Molecular modeling shows the central pore of this protein is selectively permeable to anions such as HCO(3) rather than CO(2) or O(2) (Probable). There are estimated to be 2970 CsoS1A/CsoS1C proteins per carboxysome (the proteins differ by only 1 residue) (Ref.5).^{[1] [2] [3] [4] [5] [6]} Unlike beta-carboxysomes, alpha-carboxysomes (Cb) can form without cargo protein. CsoS2 is essential for Cb formation and is also capable of targeting foreign proteins to the Cb. The Cb shell assembles with the aid of CsoS2; CsoS1A, CsoS1B and CsoS1C form the majority of the shell while CsoS4A and CsoS4B form vertices. CsoS1D forms pseudohexamers that probably control metabolite flux into and out of the shell.^{[7] [8]}

References

1. ↑ English RS, Jin S, Shively JM. Use of Electroporation To Generate a Thiobacillus neapolitanus Carboxysome Mutant. Appl Environ Microbiol. 1995 Sep;61(9):3256-60. PMID:16535117 doi:10.1128/aem.61.9.3256-3260.1995
2. ↑ Tsai Y, Sawaya MR, Cannon GC, Cai F, Williams EB, Heinhorst S, Kerfeld CA, Yeates TO. Structural analysis of CsoS1A and the protein shell of the Halothiobacillus neapolitanus carboxysome. PLoS Biol. 2007 Jun;5(6):e144. PMID:17518518 doi:10.1371/journal.pbio.0050144
3. ↑ English RS, Lorbach SC, Qin X, Shively JM. Isolation and characterization of a carboxysome shell gene from Thiobacillus neapolitanus. Mol Microbiol. 1994 May;12(4):647-54. PMID:7934888 doi:10.1111/j.1365-2958.1994.tb01052.x
4. ↑ Bonacci W, Teng PK, Afonso B, Niederholtmeyer H, Grob P, Silver PA, Savage DF. Modularity of a carbon-fixing protein organelle. Proc Natl Acad Sci U S A. 2012 Jan 10;109(2):478-83. doi:, 10.1073/pnas.1108557109. Epub 2011 Dec 19. PMID:22184212 doi:http://dx.doi.org/10.1073/pnas.1108557109
5. ↑ Dou Z, Heinhorst S, Williams EB, Murin CD, Shively JM, Cannon GC. CO2 fixation kinetics of Halothiobacillus neapolitanus mutant carboxysomes lacking carbonic anhydrase suggest the shell acts as a diffusional barrier for CO2. J Biol Chem. 2008 Apr 18;283(16):10377-84. PMID:18258595 doi:10.1074/jbc.M709285200
6. ↑ Mahinthichaichan P, Morris DM, Wang Y, Jensen GJ, Tajkhorshid E. Selective Permeability of Carboxysome Shell Pores to Anionic Molecules. J Phys Chem B. 2018 Oct 4;122(39):9110-9118. PMID:30193460 doi:10.1021/acs.jpcb.8b06822
7. ↑ Cai F, Dou Z, Bernstein SL, Leverenz R, Williams EB, Heinhorst S, Shively J, Cannon GC, Kerfeld CA. Advances in Understanding Carboxysome Assembly in Prochlorococcus and Synechococcus Implicate CsoS2 as a Critical Component. Life (Basel). 2015 Mar 27;5(2):1141-71. PMID:25826651 doi:10.3390/life5021141
8. ↑ Li T, Jiang Q, Huang J, Aitchison CM, Huang F, Yang M, Dykes GF, He HL, Wang Q, Sprick RS, Cooper AI, Liu LN. Reprogramming bacterial protein organelles as a nanoreactor for hydrogen production. Nat Commun. 2020 Oct 28;11(1):5448. doi: 10.1038/s41467-020-19280-0. PMID:33116131 doi:http://dx.doi.org/10.1038/s41467-020-19280-0
9. ↑ Li J, Li T, Wang S, Zhang YZ, Liu LN, Wang P. Symmetry-adjusted cryo-EM analysis unveils the detailed linker protein CsoS2 interactions within the α-carboxysome shell. Plant Physiol. 2025 Apr 30;198(1):kiaf165. PMID:40341945 doi:10.1093/plphys/kiaf165