8b12

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cryo-EM structure of carboxysomal mini-shell: icosahedral assembly from CsoS4A/1A and CsoS2 co-expression (T = 9)cryo-EM structure of carboxysomal mini-shell: icosahedral assembly from CsoS4A/1A and CsoS2 co-expression (T = 9)

Structural highlights

8b12 is a 10 chain structure with sequence from Halothiobacillus neapolitanus. Full crystallographic information is available from OCA. For a guided tour on the structure components use FirstGlance.
Method:Electron Microscopy, Resolution 1.86Å
Resources:FirstGlance, OCA, PDBe, RCSB, PDBsum, ProSAT

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]

Publication Abstract from PubMed

Carboxysomes are a paradigm of self-assembling proteinaceous organelles found in nature, offering compartmentalisation of enzymes and pathways to enhance carbon fixation. In alpha-carboxysomes, the disordered linker protein CsoS2 plays an essential role in carboxysome assembly and Rubisco encapsulation. Its mechanism of action, however, is not fully understood. Here we synthetically engineer alpha-carboxysome shells using minimal shell components and determine cryoEM structures of these to decipher the principle of shell assembly and encapsulation. The structures reveal that the intrinsically disordered CsoS2 C-terminus is well-structured and acts as a universal "molecular thread" stitching through multiple shell protein interfaces. We further uncover in CsoS2 a highly conserved repetitive key interaction motif, [IV]TG, which is critical to the shell assembly and architecture. Our study provides a general mechanism for the CsoS2-governed carboxysome shell assembly and cargo encapsulation and further advances synthetic engineering of carboxysomes for diverse biotechnological applications.

Intrinsically disordered CsoS2 acts as a general molecular thread for alpha-carboxysome shell assembly.,Ni T, Jiang Q, Ng PC, Shen J, Dou H, Zhu Y, Radecke J, Dykes GF, Huang F, Liu LN, Zhang P Nat Commun. 2023 Sep 7;14(1):5512. doi: 10.1038/s41467-023-41211-y. PMID:37679318[9]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.

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. ↑ Ni T, Jiang Q, Ng PC, Shen J, Dou H, Zhu Y, Radecke J, Dykes GF, Huang F, Liu LN, Zhang P. Intrinsically disordered CsoS2 acts as a general molecular thread for α-carboxysome shell assembly. Nat Commun. 2023 Sep 7;14(1):5512. PMID:37679318 doi:10.1038/s41467-023-41211-y

8b12, resolution 1.86Å

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