bims-mitpro 2025-09-21 papers

Issue of 2025–09–21
two papers selected by
Andreas Kohler, Umeå University

bioRxiv. 2025 Sep 06. pii: 2025.09.05.674599. [Epub ahead of print]

Cryo-EM Reveals Regulatory Mechanisms Governing Substrate Selection and Activation of Human LONP1.

Jeffrey T Mindrebo, Lauren Alexandrescu, Jennifer R Baker, Garret Wang, Gabriel C Lander.

The human AAA+ protease LONP1 plays a central role in maintaining mitochondrial proteostasis. LONP1 processes a vast array of substrates, ranging from damaged or unfolded proteins to specific subunits stably integrated into respiratory complexes. Previous cryo-EM studies of LONP1 uncovered two distinct conformational states corresponding to inactive or active forms of the enzyme. While these states have shed light on the intricacies of LONP1 substrate translocation and proteolytic processing, little is known about the decision-making involved in LONP1 substrate engagement and subsequent initiation of its unfoldase activity. Here, we use cryo-EM to determine a novel ADP-bound, C3-symmetric intermediate state of LONP1 (LONP1C3) with putative substrate "fold-sensing" capabilities. Our biochemical and structural data indicate that LONP1C3 is an on-pathway intermediate and that is stabilized by interaction with folded substrates. Moreover, we identify additional symmetric and asymmetric conformational states, including a two-fold symmetric split-hexamer conformation, that we associate with the transition from LONP1C3 to LONP1ENZ. We propose that the C3-state regulates substrate selection and enables LONP1 to efficiently surveil the matrix proteome to ensure selective removal of damaged and dysfunctional proteins as well as privileged LONP1 substrates. These findings collectively provide further mechanistic insights into LONP1 substrate recruitment and engagement and inform on its diverse roles in maintaining homeostasis within the mitochondria.

DOI: https://doi.org/10.1101/2025.09.05.674599

Proc Natl Acad Sci U S A. 2025 Sep 23. 122(38): e2512430122

Cryo-EM structure of the prohibitin complex in open conformation.

Sixing Hong, Zeyuan Guan, Liying Zhang, Jinjin Zhuang, Ling Yan, Yanjun Liu, Zhu Liu, Qiang Wang, Ping Yin.

Prohibitin 1 (PHB1) and Prohibitin 2 (PHB2), two conserved prohibitin members, are primarily localized to the mitochondrial inner membrane (MIM) to form a nanoscale macromolecular prohibitin complex. This prohibitin complex can facilitate the spatial organization of proteins and lipids, thus maintaining cellular metabolism and homeostasis, but its architecture remains largely unknown. Here, we report the cryo-EM structure of a prohibitin complex at 2.8 Å resolution, which contains 11 PHB1-PHB2 heterodimers. This complex displays a bell-like cage, consisting of a lid and a wall, which creates an intermembrane space-facing compartment for the MIM. The lid of the cage is stably assembled, and it is responsible for the prohibitin complex formation. In contrast, the wall of the cage is flexible and exhibits lateral openings, providing a channel for intramembrane exchange of proteins and lipids. These findings provide a structural basis for understanding the scaffold role of the prohibitin complex in organizing intramembrane proteins and lipids.

Keywords: cryo-EM; membrane microdomain; mitochondria; prohibitin complex; scaffold

DOI: https://doi.org/10.1073/pnas.2512430122