8wxb
Cryo-EM structure of the alpha-carboxysome shell vertex from Prochlorococcus MED4
Structural highlights
FunctionCSS4A_PROMP 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 (By similarity). Has not been identified in purified carboxysomes; it is expected to be present in very low amounts (Probable).[UniProtKB:O85043][1] Publication Abstract from PubMedCarboxysomes are bacterial microcompartments that encapsulate the enzymes RuBisCO and carbonic anhydrase in a proteinaceous shell to enhance the efficiency of photosynthetic carbon fixation. The self-assembly principles of the intact carboxysome remain elusive. Here we purified alpha-carboxysomes from Prochlorococcus and examined their intact structures using single-particle cryo-electron microscopy to solve the basic principles of their shell construction and internal RuBisCO organization. The 4.2 A icosahedral-like shell structure reveals 24 CsoS1 hexamers on each facet and one CsoS4A pentamer at each vertex. RuBisCOs are organized into three concentric layers within the shell, consisting of 72, 32 and up to 4 RuBisCOs at the outer, middle and inner layers, respectively. We uniquely show how full-length and shorter forms of the scaffolding protein CsoS2 bind to the inner surface of the shell via repetitive motifs in the middle and C-terminal regions. Combined with previous reports, we propose a concomitant 'outside-in' assembly principle of alpha-carboxysomes: the inner surface of the self-assembled shell is reinforced by the middle and C-terminal motifs of the scaffolding protein, while the free N-terminal motifs cluster to recruit RuBisCO in concentric, three-layered spherical arrangements. These new insights into the coordinated assembly of alpha-carboxysomes may guide the rational design and repurposing of carboxysome structures for improving plant photosynthetic efficiency. Structure and assembly of the alpha-carboxysome in the marine cyanobacterium Prochlorococcus.,Zhou RQ, Jiang YL, Li H, Hou P, Kong WW, Deng JX, Chen Y, Zhou CZ, Zeng Q Nat Plants. 2024 Apr;10(4):661-672. doi: 10.1038/s41477-024-01660-9. Epub 2024 , Apr 8. PMID:38589484[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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