Download MendeleyOccurrence and stability of hetero-hexamer associations formed by beta-carboxysome CcmK shell components.
Garcia-Alles, L.F., Root, K., Maveyraud, L., Aubry, N., Lesniewska, E., Mourey, L., Zenobi, R., Truan, G.(2019) PLoS One 14: e0223877-e0223877
- PubMed: 31603944
- DOI: https://doi.org/10.1371/journal.pone.0223877
- Primary Citation of Related Structures:
6SCR - 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.
Organizational Affiliation:
Toulouse Biotechnology Institute (TBI), Université de Toulouse, CNRS, INRA, INSA, Toulouse, France.
