Insertion of plastidic β-barrel proteins into the outer envelopes of plastids involves an intermembrane space intermediate formed with Toc75-V/OEP80

Abstract

The insertion of organellar membrane proteins with the correct topology requires the following: First, the proteins must contain topogenic signals for translocation across and insertion into the membrane. Second, proteinaceous complexes in the cytoplasm, membrane, and lumen of organelles are required to drive this process. Many complexes required for the intracellular distribution of membrane proteins have been described, but the signals and components required for the insertion of plastidic β-barrel-type proteins into the outer membrane are largely unknown. The discovery of common principles is difficult, as only a few plastidic β-barrel proteins exist. Here, we provide evidence that the plastidic outer envelope β-barrel proteins OEP21, OEP24, and OEP37 from pea (Pisum sativum) and Arabidopsis thaliana contain information defining the topology of the protein. The information required for translocation of pea proteins across the outer envelope membrane is present within the six N-terminal β-strands. This process requires the action of TOC (translocon of the outer chloroplast membrane). After translocation into the intermembrane space, β-barrel proteins interact with TOC75-V, as exemplified by OEP37 and P39, and are integrated into the membrane. The membrane insertion of plastidic β-barrel proteins is affected by mutation of the last β-strand, suggesting that this strand contributes to the insertion signal. These findings shed light on the elements and complexes involved in plastidic β-barrel protein import.

The CRL plastid outer envelope protein supports TOC75-V / OEP80 complex formation inArabidopsis

“…OEP80 is involved in the incorporation of plastidic β-barrel proteins into OEM (Gross et al, 2021). Therefore, CRL may participate in this process in conjunction with OEP80.…”

“…The copyright holder for this preprint this version posted March 11, 2023. ; https://doi.org/10.1101/2023.03.07.531578 doi: bioRxiv preprint the OEM by interacting with OEP80 (Gross et al, 2021). It has been hypothesized that additional factors are involved in this process, but none have been identified (Gross et al, 2021).…”

The Biogenesis Process of VDAC – From Early Cytosolic Events to Its Final Membrane Integration

“…In eukaryotes, the presence of β-barrel proteins is restricted to the OM of mitochondria and chloroplasts that were derived from prokaryotic ancestors. The assembly of these proteins into their corresponding OM is in each case facilitated by a dedicated protein complex that contains a highly conserved central β-barrel protein termed BamA/YaeT/Omp85 in Gram-negative bacteria, Tob55/Sam50 in mitochondria, and probably OEP80 in plastids (Ulrich and Rapaport, 2015;Gross et al, 2021). These central components are related to each other and belong to the Omp85 superfamily (Gentle et al, 2005).…”

Functional Organization of Sequence Motifs in Diverse Transit Peptides of Chloroplast Proteins

“…These nuclearencoded chloroplast proteins can be broadly categorized based on their sub-organellar locations. Proteins localized to the outer membrane of chloroplasts are primarily inserted directly into the outer membrane from the cytosol, with a few exceptions (Lee et al, 2014(Lee et al, , 2017Day et al 2019; Gross et al, 2021). However, most chloroplast interior proteins, which are localized to the inner membrane, stroma, or thylakoids, are imported into chloroplasts in a process mediated by the TOC/TIC (translocon at the outer/inner envelope of chloroplasts) translocons (Li and Chiu, 2010;Richardson et al, 2017Richardson et al, , 2018.…”