7ckb
Simplified Alpha-Carboxysome, T=3
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 PubMedBacterial microcompartments are proteinaceous shells that encase specialized metabolic processes in bacteria. Recent advances in simplification of these intricate shells have encouraged bioengineering efforts. Here, we construct minimal shells derived from the Halothiobacillus neapolitanus alpha-carboxysome, which we term Cso-shell. Using cryogenic electron microscopy, the atomic-level structures of two shell forms were obtained, reinforcing notions of evolutionarily conserved features in bacterial microcompartment shell architecture. Encapsulation peptide sequences that facilitate loading of heterologous protein cargo within the shells were identified. We further provide a first demonstration in utilizing minimal bacterial microcompartment-derived shells for hosting heterologous enzymes. Cso-shells were found to stabilize enzymatic activities against heat shock, presence of methanol co-solvent, consecutive freeze-thawing, and alkaline environments. This study yields insights into alpha-carboxysome assembly and advances the utility of synthetic bacterial microcompartments as nanoreactors capable of stabilizing enzymes with varied properties and reaction chemistries. Structure of a Minimal alpha-Carboxysome-Derived Shell and Its Utility in Enzyme Stabilization.,Tan YQ, Ali S, Xue B, Teo WZ, Ling LH, Go MK, Lv H, Robinson RC, Narita A, Yew WS Biomacromolecules. 2021 Aug 12. doi: 10.1021/acs.biomac.1c00533. PMID:34384019[4] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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