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♦ See referenced article, J. Biol. Chem. 2012, 287, 20471–20481
The chaperonin system, which helps proteins take on their native structures, in chloroplasts is an oddity. In chloroplasts, the chaperonin cofactors are encoded by multiple genes; those found in bacteria and mitochondria are encoded by single genes for each component. Not much is known about how these chloroplast chaperonin cofactors come together. In this Paper of the Week, Manajit Hayer-Hartl at the Max Planck Institute of Biochemistry and colleagues characterized the interactions of three chaperonin cofactor proteins in a green alga with the well characterized Escherichia coli chaperonin, GroEL. The investigators demonstrated that the chaperonin cofactors formed hetero-oligomeric complexes of seven 10-kDa modules. The heptamers interacted with GroEL to encapsulate proteins. Because the cofactors will modify the chemical environment of the chaperonin folding cage, the investigators suggest that the various configurations of the chaperonin cofactors may give the chaperonin system differing capabilities to help specific proteins fold.