About this Research Topic
These discoveries led to general recognition of Type I chaperonins as important protein Nano machines that play a key role in protein folding or assembly, in bacteria mitochondria, and chloroplasts. In vitro reconstitution of their protein folding activity using denatured dimeric RubisCO as model system opened the door to a new field of research, which focused on mechanistic aspects of chaperonin function. The friendly nature of the Escherichia coli chaperonins, in particular the profound stability of the protein oligomers, enabled their extensive investigation, which established them as the prototype chaperonin model system. In the ensuing years, further investigation of chaperonins from chloroplasts, mitochondria and numerous additional bacterial strains, revealed a wide range of divergence from the E. coli paradigm. In the case of chloroplast chaperonins, the most striking observation was that these chaperonins assemble into hetero-oligomeric tetradecamers that are composed of several homologous subunits, in contrast to the homooligomeric nature of bacterial chaperonins. One of them, Cpn20, is unique in that it is composed of two Hsp10 (Cpn10) like domains fused together and was implicated in numerous additional roles in the chloroplast such as activation of FeSOD or abscisic acid signaling. With regard to mitochondrial chaperonins, these were also found to exhibit unique structural properties and retain unexpected extra-organellar moonlighting functions. As such, they were found to function in a variety of processes, including signal transduction events that may regulate immunity and inflammation. The aforementioned research indicates that variations among Type one chaperonins may reflect adaptation to unique cellular environment.
This Research Topic aims at highlighting various central aspects of Type I chaperonins, including mechanistic aspects of its folding cycle, structural and functional divergences from the classic GroEL model and how they relate to moonlighting functions.
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