Biology subjects

Lu, M.-A.

Publications and source records attributed to Lu, M.-A..

3 recordsLinked to original sources

bioRxiv2025

Structural basis for prohibitin-mediated regulation of mitochondrial m-AAA protease

Mitochondrial function critically dependents on protein quality control systems, with the m-AAA protease plays a key role at the inner mitochondrial membrane (IMM). The evolutionarily conserved prohibitins (PHBs) are essential modulators of this protease across species, yet the molecular mechanisms remain unclear. Here, we present the Cryo-EM structure of the Chaetomium thermophilum PHB (CtPHB) complex, revealing a cage-like assembly composed of 11 copies of PHB1/PHB2 heterodimers. Electron microscopic and biochemical analyses suggest that m-AAA proteases are enclosed within the PHB complex through interactions mediated by their SPFH-interacting motif (SIM) exposed in the intermembrane space. Further in situ cryo-ET directly visualizes these cage-protease assemblies in native mitochondria. Disruption of their interface leads to elevated m-AAA protease activity and diminished mitochondrial stress resistance. These data establish PHB complexes as spatial organizers that compartmentalize m-AAA proteases in membrane microdomains to fine tune proteolytic homeostasis. Our findings reveal the critical role of the PHB complex in maintaining mitochondrial proteostasis, providing a unified mechanistic model to explain and reconcile the pleiotropic, and often contradictive phenotypes of PHBs and m-AAA protease in mitochondrial physiology and various disease conditions.

molecular biology↗

bioRxiv2024

Calcium Homeostasis Modulator 2 Constitutes an ATP-regulation Pore in Mitochondria

Recent structural analyses showed that the calcium homeostasis modulator-2 (CALHM2) forms a mega channel, but its cellular location and endogenous function are yet unknown. We found that native CALHM2 resides on the mitochondrial inner membrane and constitutes an ATP-regulated ATP release channel. CALHM2 knockdown/knockout decreases cytosolic ATP concentration, and thereby compromises energy-sensitive processes, such as intracellular Ca2+ handling. However, CALHM2 loss-of-function elevates ATP concentration in the mitochondrial matrix, dephosphorylates key enzymes in the mammalian target of rapamycin (mTOR) pathway, and promotes longevity in CALHM2 knockout mice. These findings reveal that CALHM2 constitutes a novel regulator of mitochondrial metabolism, which may have important implications in aging and diseases.

cell biology↗

bioRxiv2024

Molecular mechanism of the flotillin complex in membrane microdomain organization

Flotillin-1 and flotillin-2 form hetero-oligomers to create flotillin membrane microdomains essential for endocytosis and protein sorting. However, the mechanisms of flotillin oligomerization and microdomain organization remain incompletely understood. Here, we present the cryo-EM structure of human flotillin complex, showing that flotillin-1 and -2 form a 44-mer, membrane attached, and dome-shaped structure that defines a 30-nm circular membrane domain. The cryo-ET data demonstrates that while attached to the cytoplasmic leaflet in situ, flotillin complexes possess intrinsic structural plasticity on the native membrane. Each flotillin complex may represent a fundamental unit of membrane microdomains, with their clustering enabling the formation of larger and more elaborate domains. We further reveal that phosphorylation at residues Y160 (flotillin-1) and Y163 (flotillin-2) may act as a molecular switch to modulate complex assembly, potentially regulating its function in endocytosis. These findings demonstrate the molecular mechanism of flotillin-mediated membrane segregation and microdomain formation, and suggest a previously unrecognized role of flotillin in sequestrating membrane proteins.

biochemistry↗