Molecular architecture and the mechanics of Lon, a protease-chaperone machine

Abstract

The ATP-dependent Lon protease, which has orthologs distributed in all kingdoms of life, is essential in bacteria and other microorganisms under stress conditions and is needed for survival of mammalian cells subjected to oxidative damage. Lon consists of a molecular chaperone belonging to the AAA+ family and a protease with a serine-lysine catalytic dyad encoded in tandem in a single polypeptide. Here, we report the 2.0 ?resolution crystal structure of Lon from Thermococcus onnurineus NA14 (TonLon). Six subunits of TonLon assemble into a cylindrical structure with a sequestered internal chamber harboring the proteolytic active sites accessible only through restricted axial channels. Alternating subunits exist in two different nucleotide states displaying different domain orientations and intersubunit contacts indicative of the ATP hydrolysis-coupled motions driving protein unfolding and translocation.