6SMH

Cryo-electron microscopy structure of a RbcL-Raf1 supercomplex from Synechococcus elongatus PCC 7942

Summary for 6SMH

• Entry DOI: 10.2210/pdb6smh/pdb
• EMDB information: 10235
• Descriptor: Ribulose bisphosphate carboxylase large chain, Rubisco accumulation factor 1 (RAF1) peptide (2 entities in total)
• Functional Keywords: rubisco, rubisco accumulation factor1, raf1, synechococcus elongatus 7942, cyanobacteria, photosynthesis
• Biological source: Synechococcus elongatus (strain PCC 7942 / FACHB-805); More
• Total number of polymer chains: 16
• Total formula weight: 570542.24

Authors

Huang, F.,Kong, W.-W.,Sun, Y.,Chen, T.,Dykes, G.F.,Jiang, Y.L.,Liu, L.N. (deposition date: 2019-08-21, release date: 2020-07-08, Last modification date: 2024-05-15)

Primary citation

Huang, F.,Kong, W.W.,Sun, Y.,Chen, T.,Dykes, G.F.,Jiang, Y.L.,Liu, L.N.
Rubisco accumulation factor 1 (Raf1) plays essential roles in mediating Rubisco assembly and carboxysome biogenesis.
Proc.Natl.Acad.Sci.USA, 117:17418-17428, 2020

PubMed Abstract: Carboxysomes are membrane-free organelles for carbon assimilation in cyanobacteria. The carboxysome consists of a proteinaceous shell that structurally resembles virus capsids and internal enzymes including ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco), the primary carbon-fixing enzyme in photosynthesis. The formation of carboxysomes requires hierarchical self-assembly of thousands of protein subunits, initiated from Rubisco assembly and packaging to shell encapsulation. Here we study the role of Rubisco assembly factor 1 (Raf1) in Rubisco assembly and carboxysome formation in a model cyanobacterium, PCC7942 (Syn7942). Cryo-electron microscopy reveals that Raf1 facilitates Rubisco assembly by mediating RbcL dimer formation and dimer-dimer interactions. Syn7942 cells lacking Raf1 are unable to form canonical intact carboxysomes but generate a large number of intermediate assemblies comprising Rubisco, CcaA, CcmM, and CcmN without shell encapsulation and a low abundance of carboxysome-like structures with reduced dimensions and irregular shell shapes and internal organization. As a consequence, the Raf1-depleted cells exhibit reduced Rubisco content, CO-fixing activity, and cell growth. Our results provide mechanistic insight into the chaperone-assisted Rubisco assembly and biogenesis of carboxysomes. Advanced understanding of the biogenesis and stepwise formation process of the biogeochemically important organelle may inform strategies for heterologous engineering of functional CO-fixing modules to improve photosynthesis.

PubMed: 32636267
DOI: 10.1073/pnas.2007990117

Experimental method

ELECTRON MICROSCOPY (4.3 Å)