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Cryo-EM structure of carboxysomal midi-shell: icosahedral assembly from CsoS4A/4B/1A/1B/1C/1D and CsoS2 C-terminal co-expression (T = 16)Cryo-EM structure of carboxysomal midi-shell: icosahedral assembly from CsoS4A/4B/1A/1B/1C/1D and CsoS2 C-terminal co-expression (T = 16)
Structural highlights
FunctionCSS4A_HALNC Probably forms vertices in the carboxysome, a polyhedral inclusion where RuBisCO (ribulose bisphosphate carboxylase, cbbL-cbbS) is sequestered. Has been modeled to induce curvature upon insertion into an otherwise flat hexagonal layer of major carboxysome subunits (Probable). A minor shell protein, only 12 pentamers of CsoS4A/CsoS4B are calculated to be present in each carboxysome. The 2 CsoS4 proteins contribute to the impermeability of the carboxysome to CO(2) (PubMed:19844578).[1] [2] 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.[3] Publication Abstract from PubMedIntracellular compartmentalization enhances biological reactions, crucial for cellular function and survival. An example is the carboxysome, a bacterial microcompartment for CO(2) fixation. The carboxysome uses a polyhedral protein shell made of hexamers, pentamers, and trimers to encapsulate Rubisco, increasing CO(2) levels near Rubisco to enhance carboxylation. Despite their role in the global carbon cycle, the molecular mechanisms behind carboxysome shell assembly remain unclear. Here, we present a structural characterization of alpha-carboxysome shells generated from recombinant systems, which contain all shell proteins and the scaffolding protein CsoS2. Atomic-resolution cryo-electron microscopy of the shell assemblies, with a maximal size of 54 nm, unveil diverse assembly interfaces between shell proteins, detailed interactions of CsoS2 with shell proteins to drive shell assembly, and the formation of heterohexamers and heteropentamers by different shell protein paralogs, facilitating the assembly of larger empty shells. Our findings provide mechanistic insights into the construction principles of alpha-carboxysome shells and the role of CsoS2 in governing alpha-carboxysome assembly and functionality. Molecular principles of the assembly and construction of a carboxysome shell.,Wang P, Li J, Li T, Li K, Ng PC, Wang S, Chriscoli V, Basle A, Marles-Wright J, Zhang YZ, Liu LN Sci Adv. 2024 Nov 29;10(48):eadr4227. doi: 10.1126/sciadv.adr4227. Epub 2024 Nov , 29. PMID:39612341[4] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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