9IV3

Crystal structure of CcmS-CcmK1 complex from Synechocystis sp. PCC 6803

Summary for 9IV3

• Entry DOI: 10.2210/pdb9iv3/pdb
• Descriptor: Carboxysome shell protein CcmK1, Slr1911 protein (3 entities in total)
• Functional Keywords: cyanobacteria, co2-concentrating mechanism, carboxysome assembly, shell proteins, chaperone
• Biological source: Synechocystis sp. PCC 6803 substr. Kazusa; More
• Total number of polymer chains: 8
• Total formula weight: 112345.76

Authors

Li, J.,Deng, J.X.,Jiang, Y.L.,Zhou, C.Z. (deposition date: 2024-07-22, release date: 2025-03-12, Last modification date: 2025-08-06)

Primary citation

Li, J.,Deng, J.X.,Chen, X.,Li, B.,Li, B.R.,Zhu, Z.L.,Liu, J.,Chen, Y.,Mi, H.,Zhou, C.Z.,Jiang, Y.L.
Assembly mechanism of the beta-carboxysome shell mediated by the chaperone CcmS.
New Phytol., 246:1676-1690, 2025

PubMed Abstract: Carboxysomes are self-assembled bacterial microcompartments (BMCs) that encapsulate the enzymes RuBisCO and carbonic anhydrase into a proteinaceous shell, enhancing the efficiency of photosynthetic carbon fixation. The chaperone CcmS was reported to participate in the assembly of β-carboxysomes; however, the underlying molecular mechanism remains elusive. We report the crystal structure of CcmS from Synechocystis sp. PCC 6803, revealing a monomer of α/β fold. Moreover, its complex structures with two types of BMC hexamers, CcmK1 homohexamer and CcmK1-CcmK2 heterohexamer, reveal a same pattern of CcmS binding to the featured C-terminal segment of CcmK1. Upon binding to CcmS, this C-terminal segment of CcmK1 is folded into an amphipathic α-helix protruding outward that might function as a hinge to crosslink adjacent BMC-H hexamers, thereby facilitating concerted and precise assembly of the β-carboxysome shell. Deletion of the ccmS gene or the 8-residue C-terminal coding region of ccmK1 resulted in the formation of aberrant and fewer carboxysomes, suppressed photosynthetic capacity in Synechocystis sp. PCC 6803. These findings enable us to propose a putative model for the chaperone-assisted assembly of β-carboxysome shell and provide clues for the design and engineering of efficient carbon fixation machinery.

PubMed: 40125605
DOI: 10.1111/nph.70086

Experimental method

X-RAY DIFFRACTION (2.95 Å)