The Mgr2 subunit of the TIM23 complex regulates membrane insertion of marginal stop‐transfer signals in the mitochondrial inner membrane

Abstract

The TIM23 complex mediates membrane insertion of presequence‐containing mitochondrial proteins via a stop‐transfer mechanism. Stop‐transfer signals consist of hydrophobic transmembrane segments and flanking charges. Mgr2 functions as a lateral gatekeeper of the TIM23 complex. However, it remains elusive which features of stop‐transfer signals are discriminated by Mgr2. To determine the effects of Mgr2 on the TIM23‐mediated stop‐transfer pathway, we measured membrane insertion of model transmembrane segments of varied hydrophobicity and flanking charges in Mgr2‐deletion or ‐overexpression yeast strains. We found that upon deletion of Mgr2, the threshold hydrophobicity for membrane insertion, as well as the requirement for matrix‐facing positive charges, is reduced. These results imply that the Mgr2‐mediated gatekeeper function is important for controlling membrane sorting of marginal stop‐transfer signals.

Central role of Tim17 in mitochondrial presequence protein translocation

“…1e–g ), and association with Mgr2 might reduce the contact to the bilayer as much as possible. (3) The translocation at the Tim17 bilayer interface enables the lateral release of a subsequent transmembrane domain/stop-transfer signal of inner membrane-sorted proteins likely by dissociation of Mgr2, in agreement with the report that Mgr2 modulates the threshold hydrophobicity for membrane insertion 55 .

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Interactions of amyloidogenic proteins with mitochondrial protein import machinery in aging-related neurodegenerative diseases

“…Soluble precursor proteins are then translocated completely into the matrix by the TIM23 MOTOR complex, whereby the ATPase activity of mtHsp70, modulated by co-chaperones DnaJC15/19 and Magmas-1/2, pulls the substrate by a Brownian ratchet or active pulling mechanism (Mokranjac et al, 2003a;Mokranjac, 2020;Silva et al, 2003;Mokranjac et al, 2003b;Truscott et al, 2003). By contrast, when a hydrophobic stop-transfer sequence is detected on the substrate, translocation stalls, the complex recruits subunits of the TIM23 SORT complex, and the nonpolar segment partitions laterally into the MIM as an α-helical transmembrane segment in a manner driven by the Δψ m (Gartner et al, 1995;Gruhler et al, 1997) and mediated by the ROMO1 and Tim21 gatekeepers (van der Laan et al, 2006;Mick et al, 2012;Ieva et al, 2014;Richter-Dennerlein et al, 2016;Richter et al, 2019;Lee et al, 2020). Notably, an alternative structure-based model of TIM23 function suggests that instead of forming an aqueous channel, Tim23 and Tim17 together form lipid-exposed cavities that provide a protein translocation pathway (Sim et al, 2023), consistent with evidence that TIM23 precursors are translocated across the MIM at the Tim17-bilayer interface rather than via a channel defined by Tim23 (Fielden et al, 2023).…”

Viaje al centro de la mitocondria: importación de proteínas, sus alteraciones y enfermedades relacionadas

“…En este caso la señal indica que las proteínas deben ser insertadas en la membrana interna mitocondrial en un proceso denominado "transferencia detenida" (en inglés Stop Transfer; Glick et al, 1992;van der Laan et al, 2007). En estos casos, la MTS se expone a la matriz; sin embargo, el cruce transmembranal se retiene en 2021 https://doi.org/10.22201/fesz.23958723e.2021.370 el canal de TIM23 y la proteína es liberada lateralmente con ayuda de la proteína Mgr2 (Ieva et al, 2014;Lee et al, 2020;Matta, Kumar & D'Silva, 2020). Ejemplos de proteínas que siguen esta ruta de importación son los citocromos c 1 y b 2 (Glick et al, 1992).…”