Crystal structure of Lon protease: molecular architecture of gated entry to a sequestered degradation chamber

Lon proteases are distributed in all kingdoms of life and are required for survival of cells under stress. Lon is a tandem fusion of an AAA + molecular chaperone and a protease with a serine-lysine catalytic dyad. We report the 2.0-angstrom resolution crystal structure of Thermococcus onnurineus NA1 Lon (TonLon). The structure is a three-tiered hexagonal cylinder with a large sequestered chamber accessible through an axial channel. Conserved loops extending from the AAA + domain combine with an insertion domain containing the membrane anchor to form an apical domain that serves as a gate governing substrate access to an internal unfolding and degradation chamber. Alternating AAA + domains are in tight- and weak-binding nucleotide states with different domain orientations and intersubunit contacts, reflecting intramolecular dynamics during ATP-driven protein unfolding and translocation. The bowl-shaped proteolytic chamber is contiguous with the chaperone chamber allowing internalized proteins direct access to the proteolytic sites without further gating restrictions. The EMBO Journal (2010) 29, 3520-3530. doi:10.1038/emboj.2010.226; Published online 10 September 2010 Subject Categories: proteins; structural biology