The outer membrane form of the mitochondrial protein Mcr1 follows a TOM‐independent membrane insertion pathway

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149

141

Tail-anchored proteins form a distinct class of membrane proteins that are found in all intracellular membranes exposed to the cytosol. These proteins have a single membrane insertion sequence at their C-terminus and display a large N-terminal portion to the cytosol. Despite their importance for various cellular processes, the mechanisms by which these proteins are recognized at and inserted into their corresponding target membrane remained largely unclear. Here we address this issue and investigate the biogenesis of tail-anchored proteins residing in the mitochondrial outer membrane. To that goal we developed a highly specific assay to monitor the membrane insertion of the model tail-anchored protein Fis1. Using this assay, we show that in contrast to all other import pathways in yeast mitochondria, none of the import components at the outer membrane is involved in the insertion process of Fis1. Both the steady-state levels of Fis1 and its in vitro insertion into isolated mitochondria were unaffected when mitochondria mutated in known import factors were analyzed. Fis1 was inserted into lipid vesicles, and importantly, elevated ergosterol contents in these vesicles inhibited this insertion. Collectively, these results suggest that Fis1 is inserted into mitochondria in a novel pathway where the unique lipid composition of the mitochondrial outer membrane contributes to the selectivity of the process. Thus, this work demonstrates a novel role for lipids in the biogenesis of mitochondrial protein.

Section: Resultsmentioning

confidence: 99%

Integration of tail-anchored proteins into the mitochondrial outer membrane does not require any known import components

Kemper

Habib

Engl

et al. 2008

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149

141

“…Conceptually, this could be a simple process that requires no additional protein factors and involves the spontaneous partitioning of newly synthesised proteins into the lipid bilayer. Although there is some data to suggest that such completely unassisted biogenesis of tail-anchored proteins might occur at the mitochondrial outer membrane Meineke et al, 2008;Setoguchi et al, 2006), most studies suggest that the biogenesis of tail-anchored proteins at the ER involves one or more cytosolic factors (Abell et al, 2007;Colombo et al, 2009;Favaloro et al, 2008;Rabu et al, 2008;Yabal et al, 2003) (Fig. 1).…”

Section: Introductionmentioning

confidence: 99%

Biogenesis of tail-anchored proteins: the beginning for the end?

Rabu

Schmid

Schwappach

et al. 2009

114

147

Tail-anchored proteins are a distinct class of integral membrane proteins located in several eukaryotic organelles, where they perform a diverse range of functions. These proteins have in common the C-terminal location of their transmembrane anchor and the resulting post-translational nature of their membrane insertion, which, unlike the co-translational membrane insertion of most other proteins, is not coupled to ongoing protein synthesis. The study of tail-anchored proteins has provided a paradigm for understanding the components and pathways that mediate post-translational biogenesis of membrane proteins at the endoplasmic reticulum. In this Commentary, we review recent studies that have converged at a consensus regarding the molecular mechanisms that underlie this process – namely, that multiple pathways underlie the biogenesis of tail-anchored proteins at the endoplasmic reticulum.

“…Some evidence exists that tail-and signal-anchored proteins insert into the MOM without participation of a dedicated insertion machinery (Setoguchi et al, 2006;Kemper et al, 2008;Meineke et al, 2008). Other reports suggest a partial overlap in insertion pathways of polytopic and TA proteins (Rojo et al, 2002;Otera et al, 2007).…”

Section: Introductionmentioning

confidence: 99%

A crucial role of Mim2 in the biogenesis of mitochondrial outer membrane proteins

Dimmer

Papić

Schumann

et al. 2012

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SummaryMost of the mitochondrial outer membrane (MOM) proteins contain helical transmembrane domains. Some of the single-span proteins and all known multiple-span proteins are inserted into the membrane in a pathway that depends on the MOM protein Mitochondrial Import 1 (Mim1). So far it has been unknown whether additional proteins are required for this process. Here, we describe the identification and characterization of Mim2, a novel protein of the MOM that has a crucial role in the biogenesis of MOM helical proteins. Mim2 physically and genetically interacts with Mim1, and both proteins form the MIM complex. Cells lacking Mim2 exhibit a severely reduced growth rate and lower steady-state levels of helical MOM proteins. In addition, absence of Mim2 leads to compromised assembly of the translocase of the outer mitochondrial membrane (TOM complex), hampered mitochondrial protein import, and defects in mitochondrial morphology. In summary, the current study demonstrates that Mim2 is a novel central player in the biogenesis of MOM proteins.