Abstact

FtsH, an AAA + metalloprotease that is essential in bacteria and eukaryotic organelles, maintains cellular homeostasis by degrading misfolded and membrane-associated proteins. Here, we report cryo-EM structures of the Escherichia coli FtsH periplasmic domain (FtsH-PD) revealing insights into its intrinsic conformational flexibility. Our analysis resolved two distinct states: a 4.9 A structure exhibiting the conserved alpha + beta fold and a 7.3 A map representing distinct rotated-helix conformation characterized by 20 degrees clockwise rotation of two alpha helices. These findings support a model where conformational changes are present not only in the FtsH cytosolic domain but also in the periplasmic domain. This flexibility potentially facilitates substrate translocation through a combination of mechanisms involving both the FtsH-PD and the HflKC complexed with FtsH, along with lipid-scramblase activity, to assist in membrane protein extraction. This study offers new perspectives on how conformational changes in the periplasmic domain contribute to FtsH substrate degradation mechanisms.