Membrane contact site detection (MCS-DETECT) reveals dual control of rough mitochondria-ER contacts

Abstract

The identification and morphological analysis of mitochondria-ER contacts (MERCs) by fluores-cent microscopy is limited by sub-pixel resolution inter-organelle distances. Here, application of a novel Membrane Contact Site (MCS) detection algorithm, MCS-DETECT, to 3D STED super-resolution images reconstructs sub-resolution organelle interactions, identifying diverse MERCs. By EM, elongated ribosome-studded riboMERCs are present in HT-1080 but not COS-7 cells and, correspondingly, MCS-DETECT identifies extended large MERCs selectively in HT-1080. These are morphologically distinct from smaller smooth contacts in COS-7 cells and larger contacts in-duced in COS-7 cells by expression of an mitochondria-ER linker. Large riboMERC expression is reduced in Gp78 knockout HT-1080 cells and their induction by Gp78 in COS-7 cells is dependent on Gp78 ubiquitin ligase activity. Gp78-dependent riboMERCs present complex tubular shapes that intercalate between and contact multiple mitochondria. MCS-DETECT of whole cell super res-olution 3D image volumes therefore identifies a novel convoluted tubular morphology for ribo-MERCs whose formation is dependent on Gp78 ubiquitin ligase activity.

Ribosome-binding protein 1, RRBP1, maintains peroxisomal biogenesis

“…RRBP1 was originally identified as a ribosome receptor for the ER (Savitz and Meyer, 1990); it was also proposed to interact with microtubules (Ogawa-Goto et al, 2007) and microtubule-dependent motor protein, kinesin (Diefenbach et al, 2004). Recent studies suggest that RRBP1 plays a role in tethering ER with mitochondria (Anastasia et al, 2021; Cardoen et al, 2024; Hung et al, 2017) and regulates mitophagy (Killackey et al, 2023). However, RRBP1 has never been linked to peroxisomal function before.…”

“…RRBP1 was previously shown to be involved in contact between ER and mitochondria (Anastasia et al, 2021; Cardoen et al, 2024; Hung et al, 2017). Thus, the fraction of mitochondria associated with wrapped by curved sheets of rough ER was enriched in RRBP1 protein compared to the ER control fraction.…”