Cryo-EM structure of the FtsH periplasmic domain reveals functional dynamics

FtsH, an essential AAA+ metalloprotease, 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 conformational flexibility. Initial 2D class averages suggested three distinct orientations, right-handed and left-handed maps of FtsH-PD, and a map with a different conformation. The 4.9Å structure of FtsH-PD exhibits the conserved α+β fold, while the 7.3Å map with the different conformation displays a 20° 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 and potentially facilitate 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 points out novel perspectives on how conformational changes in the periplasmic domain contribute to FtsH substrate degradation mechanisms.