Molecular chaperone functions in plastids

Abstract

Molecular chaperones play essential roles in a wide variety of cellular processes, from de-novo protein folding to protein disaggregation under stress conditions, unfolding and re-folding of misfolded proteins, protein degradation, protein transport and proteome remodeling during development. Almost all cell compartments contain chaperone activity to some extent, hence it is not surprising that a large number of chaperones also play essential roles in the plastid compartment. Here, the focus of chaperone activity is on protein targeting (protein import and assembly of complexes in target membranes) as well as protection from specific chloroplast-derived stresses. Moreover, chaperones play important roles in denovo folding of plastid-encoded proteins, in the folding of soluble proteins after import and processing of the transit peptides, and in protein degradation. The four major groups of molecular chaperones, the chaperonin/Cpn60, Hsp70, Hsp90 and Hsp100 families of chaperones, are all present in plastids but many cofactors and co-chaperones have not yet been identified. Although chaperone function is generally conserved, it seems that plastid-localized chaperones have evolved some specific functions and mechanisms. Current research on plastid-localized chaperones focuses therefore on the specificities of chaperone function in the context of their plastid environment and requirements.