6SCR

Structure of CcmK4 from Synechocystis sp. PCC6803

Summary for 6SCR

• Entry DOI: 10.2210/pdb6scr/pdb
• Descriptor: Carbon dioxide-concentrating mechanism protein CcmK homolog 4, 1,2-ETHANEDIOL (3 entities in total)
• Functional Keywords: bacterial micro-compartment, carboxysome, ccmk4, 2d assembly, structural protein
• Biological source: Synechocystis sp. (strain PCC 6803 / Kazusa)
• Total number of polymer chains: 2
• Total formula weight: 27789.58

Authors

Maveyraud, L.,Garcia-Alles, L.F.,Mourey, L. (deposition date: 2019-07-25, release date: 2019-10-23, Last modification date: 2024-01-24)

Primary citation

Garcia-Alles, L.F.,Root, K.,Maveyraud, L.,Aubry, N.,Lesniewska, E.,Mourey, L.,Zenobi, R.,Truan, G.
Occurrence and stability of hetero-hexamer associations formed by beta-carboxysome CcmK shell components.
Plos One, 14:e0223877-e0223877, 2019

PubMed Abstract: The carboxysome is a bacterial micro-compartment (BMC) subtype that encapsulates enzymatic activities necessary for carbon fixation. Carboxysome shells are composed of a relatively complex cocktail of proteins, their precise number and identity being species dependent. Shell components can be classified in two structural families, the most abundant class associating as hexamers (BMC-H) that are supposed to be major players for regulating shell permeability. Up to recently, these proteins were proposed to associate as homo-oligomers. Genomic data, however, demonstrated the existence of paralogs coding for multiple shell subunits. Here, we studied cross-association compatibilities among BMC-H CcmK proteins of Synechocystis sp. PCC6803. Co-expression in Escherichia coli proved a consistent formation of hetero-hexamers combining CcmK1 and CcmK2 or, remarkably, CcmK3 and CcmK4 subunits. Unlike CcmK1/K2 hetero-hexamers, the stoichiometry of incorporation of CcmK3 in associations with CcmK4 was low. Cross-interactions implicating other combinations were weak, highlighting a structural segregation of the two groups that could relate to gene organization. Sequence analysis and structural models permitted the localization of interactions that would favor formation of CcmK3/K4 hetero-hexamers. The crystallization of these CcmK3/K4 associations conducted to the elucidation of a structure corresponding to the CcmK4 homo-hexamer. Yet, subunit exchange could not be demonstrated in vitro. Biophysical measurements showed that hetero-hexamers are thermally less stable than homo-hexamers, and impeded in forming larger assemblies. These novel findings are discussed within the context of reported data to propose a functional scenario in which minor CcmK3/K4 incorporation in shells would introduce sufficient local disorder as to allow shell remodeling necessary to adapt rapidly to environmental changes.

PubMed: 31603944
DOI: 10.1371/journal.pone.0223877

Experimental method

X-RAY DIFFRACTION (1.8 Å)