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Structure of CsoS4B from Halothiobacillus neapolitanus
Structural highlights
FunctionCSS4B_HALNC Probably forms vertices in the carboxysome. 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). Its central pore is probably too small to allow passage of metabolites; its function might be to anchor different proteins or metabolites to the carboxysome (Probable).[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 PubMedCarboxysome, encapsulating an enzymatic core within an icosahedral-shaped semipermeable protein shell, could enhance CO2 fixation under low CO2 conditions in the environment. The shell of Halothiobacillus neapolitanus alpha-carboxysome possesses two 38% sequence-identical pentameric proteins, namely CsoS4A and CsoS4B. However, the functions of two paralogous pentameric proteins in alpha-carboxysome assembly remain unknown. Here we report the crystal structure of CsoS4B at 2.15A resolution. It displays as a stable pentamer, each subunit of which consists of a beta-barrel core domain, in addition to an insertion of helix alpha1 that forms the central pore. Structural comparisons and multiple-sequence alignment strongly indicate that CsoS4A and CsoS4B differ from each other in interacting with various components of alpha-carboxysome, despite they share a similar overall structure. These findings provide the structural basis for further investigations on the self-assembly process of carboxysome. Crystal structure of pentameric shell protein CsoS4B of Halothiobacillus neapolitanus alpha-carboxysome.,Zhao YY, Jiang YL, Chen Y, Zhou CZ, Li Q Biochem Biophys Res Commun. 2019 Jul 30;515(3):510-515. doi:, 10.1016/j.bbrc.2019.05.047. Epub 2019 Jun 3. PMID:31171360[4] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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