Catalytic cycling of human mitochondrial Lon protease

Structure. 2022 Sep 1;30(9):1254-1268.e7. doi: 10.1016/j.str.2022.06.006. Epub 2022 Jul 22.


The mitochondrial Lon protease (LonP1) regulates mitochondrial health by removing redundant proteins from the mitochondrial matrix. We determined LonP1 in eight nucleotide-dependent conformational states by cryoelectron microscopy (cryo-EM). The flexible assembly of N-terminal domains had 3-fold symmetry, and its orientation depended on the conformational state. We show that a conserved structural motif around T803 with a high similarity to the trypsin catalytic triad is essential for proteolysis. We show that LonP1 is not regulated by redox potential, despite the presence of two conserved cysteines at disulfide-bonding distance in its unfoldase core. Our data indicate how sequential ATP hydrolysis controls substrate protein translocation in a 6-fold binding change mechanism. Substrate protein translocation, rather than ATP hydrolysis, is a rate-limiting step, suggesting that LonP1 is a Brownian ratchet with ATP hydrolysis preventing translocation reversal. 3-fold rocking motions of the flexible N-domain assembly may assist thermal unfolding of the substrate protein.

Keywords: AAA+ protein; chaperone; molecular motor; proteolysis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • ATP-Dependent Proteases / genetics
  • ATP-Dependent Proteases / metabolism
  • Adenosine Triphosphate / metabolism
  • Cryoelectron Microscopy
  • Humans
  • Mitochondria / metabolism
  • Mitochondrial Proteins / metabolism
  • Protease La* / genetics
  • Protease La* / metabolism


  • Mitochondrial Proteins
  • Adenosine Triphosphate
  • ATP-Dependent Proteases
  • LONP1 protein, human
  • Protease La