Archaeal Chaperonins: A Cornucopia of Information and Tools to Understand the Human Chaperoning System and Its Diseases

Abstract

The chaperoning system in organisms across Archaea, Bacteria, and Eukarya encompasses a wide range of complexities. This range extends from the very simple, consisting of a few genes-proteins in the most primitive archaea to the extremely complex like the one in humans (made of many chaperones, co-chaperones, and chaperone cofactors and close interactors/receptors) and including various degrees of complexity in between. Diseases caused by defects in the chaperoning system, named chaperonopathies, are important because many are widespread and frequent and can be life threatening. Chaperonopathies are genetic or acquired. The former are caused by mutations of chaperone genes, whereas the acquired chaperonopathies are typically caused by posttranslational modifications of the chaperone proteins. In both instances, the affected chaperones are nonfunctional, or function incorrectly (e.g., gain of function), or their levels/functioning is increased or decreased. Little is known on the impact of mutations or posttranslational modifications on the properties of the chaperone molecule or on its chaperoning functions. Studies are hindered by the extreme complexity of the chaperoning machines and networks in humans and by the scarcity of experimental models. Here, we report on some archaeal chaperoning systems, focusing on the chaperonins only, which are suitable for standardizing experimental models mimicking the human situations observed in chaperonopathies. We discuss archaeal chaperonins that are similar to those of humans and present an illustrative example of the use of one of these archaeal chaperonins to elucidate the molecular abnormalities generated by a pathogenic mutation in a human chaperonin subunit that causes neuropathy.