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Mehlhorn DG, Asseck LY, Grefen C. Looking for a safe haven: tail-anchored proteins and their membrane insertion pathways. Plant Physiol 2021; 187:1916-1928. [PMID: 35235667 PMCID: PMC8644595 DOI: 10.1093/plphys/kiab298] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/15/2021] [Accepted: 06/05/2021] [Indexed: 06/14/2023]
Abstract
Insertion of membrane proteins into the lipid bilayer is a crucial step during their biosynthesis. Eukaryotic cells face many challenges in directing these proteins to their predestined target membrane. The hydrophobic signal peptide or transmembrane domain (TMD) of the nascent protein must be shielded from the aqueous cytosol and its target membrane identified followed by transport and insertion. Components that evolved to deal with each of these challenging steps range from chaperones to receptors, insertases, and sophisticated translocation complexes. One prominent translocation pathway for most proteins is the signal recognition particle (SRP)-dependent pathway which mediates co-translational translocation of proteins across or into the endoplasmic reticulum (ER) membrane. This textbook example of protein insertion is stretched to its limits when faced with secretory or membrane proteins that lack an amino-terminal signal sequence or TMD. Particularly, a large group of so-called tail-anchored (TA) proteins that harbor a single carboxy-terminal TMD require an alternative, post-translational insertion route into the ER membrane. In this review, we summarize the current research in TA protein insertion with a special focus on plants, address challenges, and highlight future research avenues.
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Affiliation(s)
- Dietmar G Mehlhorn
- Faculty of Biology and Biotechnology, Molecular and Cellular Botany, University of Bochum, Universitätsstraße 150, 44780 Bochum, Germany
| | - Lisa Y Asseck
- Faculty of Biology and Biotechnology, Molecular and Cellular Botany, University of Bochum, Universitätsstraße 150, 44780 Bochum, Germany
| | - Christopher Grefen
- Faculty of Biology and Biotechnology, Molecular and Cellular Botany, University of Bochum, Universitätsstraße 150, 44780 Bochum, Germany
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Denninger P, Reichelt A, Schmidt VAF, Mehlhorn DG, Asseck LY, Stanley CE, Keinath NF, Evers JF, Grefen C, Grossmann G. Distinct RopGEFs Successively Drive Polarization and Outgrowth of Root Hairs. Curr Biol 2019; 29:1854-1865.e5. [PMID: 31104938 DOI: 10.1016/j.cub.2019.04.059] [Citation(s) in RCA: 57] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2019] [Revised: 04/01/2019] [Accepted: 04/23/2019] [Indexed: 11/24/2022]
Abstract
Root hairs are tubular protrusions of the root epidermis that significantly enlarge the exploitable soil volume in the rhizosphere. Trichoblasts, the cell type responsible for root hair formation, switch from cell elongation to tip growth through polarization of the growth machinery to a predefined root hair initiation domain (RHID) at the plasma membrane. The emergence of this polar domain resembles the establishment of cell polarity in other eukaryotic systems [1-3]. Rho-type GTPases of plants (ROPs) are among the first molecular determinants of the RHID [4, 5], and later play a central role in polar growth [6]. Numerous studies have elucidated mechanisms that position the RHID in the cell [7-9] or regulate ROP activity [10-18]. The molecular players that target ROPs to the RHID and initiate outgrowth, however, have not been identified. We dissected the timing of the growth machinery assembly in polarizing hair cells and found that positioning of molecular players and outgrowth are temporally separate processes that are each controlled by specific ROP guanine nucleotide exchange factors (GEFs). A functional analysis of trichoblast-specific GEFs revealed GEF3 to be required for normal ROP polarization and thus efficient root hair emergence, whereas GEF4 predominantly regulates subsequent tip growth. Ectopic expression of GEF3 induced the formation of spatially confined, ROP-recruiting domains in other cell types, demonstrating the role of GEF3 to serve as a membrane landmark during cell polarization.
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Affiliation(s)
- Philipp Denninger
- Centre for Organismal Studies (COS), Heidelberg University, Im Neuenheimer Feld 230, 69120 Heidelberg, Germany
| | - Anna Reichelt
- Centre for Organismal Studies (COS), Heidelberg University, Im Neuenheimer Feld 230, 69120 Heidelberg, Germany
| | - Vanessa A F Schmidt
- Centre for Organismal Studies (COS), Heidelberg University, Im Neuenheimer Feld 230, 69120 Heidelberg, Germany
| | - Dietmar G Mehlhorn
- Center for Plant Molecular Biology, Developmental Genetics, University of Tübingen, Auf der Morgenstelle 32, 72076 Tübingen, Germany
| | - Lisa Y Asseck
- Center for Plant Molecular Biology, Developmental Genetics, University of Tübingen, Auf der Morgenstelle 32, 72076 Tübingen, Germany
| | - Claire E Stanley
- Institute for Chemical and Bioengineering, ETH Zürich, Vladimir-Prelog-Weg 1, 8093 Zürich, Switzerland; Agroecology and Environment Research Division, Agroscope, Reckenholzstrasse 191, 8046 Zürich, Switzerland
| | - Nana F Keinath
- Centre for Organismal Studies (COS), Heidelberg University, Im Neuenheimer Feld 230, 69120 Heidelberg, Germany
| | - Jan-Felix Evers
- Centre for Organismal Studies (COS), Heidelberg University, Im Neuenheimer Feld 230, 69120 Heidelberg, Germany
| | - Christopher Grefen
- Center for Plant Molecular Biology, Developmental Genetics, University of Tübingen, Auf der Morgenstelle 32, 72076 Tübingen, Germany
| | - Guido Grossmann
- Centre for Organismal Studies (COS), Heidelberg University, Im Neuenheimer Feld 230, 69120 Heidelberg, Germany; Excellence Cluster CellNetworks, Heidelberg University, Im Neuenheimer Feld 267, 69120 Heidelberg, Germany.
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Abstract
Protein-protein interactions (PPIs) play vital roles in all subcellular processes and a number of tools have been developed for their detection and analysis. Each method has its unique set of benefits and drawbacks that need to be considered prior to their application. In fact, researchers are spoilt for choice when it comes to deciding which method to use for the initial detection of a PPI, and which to corroborate the findings. With constant improvements in microscope development, the possibilities of techniques to study PPIs in vivo, and in real time, are continuously enhanced, and expanded. Here, we describe three common approaches, their recent improvements incorporating a 2in1-cloning approach, and their application in plant cell biology: ratiometric Bimolecular Fluorescence Complementation (rBiFC), FRET Acceptor Photobleaching (FRET-AB), and Fluorescent Lifetime Imaging (FRET-FLIM), using Nicotiana benthamiana leaves and Arabidopsis thaliana cell culture protoplasts as transient expression systems.
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Affiliation(s)
- Dietmar G Mehlhorn
- Centre for Plant Molecular Biology, University of Tübingen, Auf der Morgenstelle 32, 72076, Tübingen, Germany
| | - Niklas Wallmeroth
- Centre for Plant Molecular Biology, Developmental Genetics, University of Tübingen, Auf der Morgenstelle 32, 72076, Tübingen, Germany
| | - Kenneth W Berendzen
- Centre for Plant Molecular Biology, University of Tübingen, Auf der Morgenstelle 32, 72076, Tübingen, Germany
| | - Christopher Grefen
- Centre for Plant Molecular Biology, Developmental Genetics, University of Tübingen, Auf der Morgenstelle 32, 72076, Tübingen, Germany.
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Vitali DG, Sinzel M, Bulthuis EP, Kolb A, Zabel S, Mehlhorn DG, Costa BF, Farkas Á, Clancy A, Schuldiner M, Grefen C, Schwappach B, Borgese N, Rapaport D. The GET pathway can increase the risk of mitochondrial outer membrane proteins to be mistargeted to the ER. J Cell Sci 2018; 131:jcs.211110. [DOI: 10.1242/jcs.211110] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2017] [Accepted: 04/10/2018] [Indexed: 01/23/2023] Open
Abstract
Tail-anchored (TA) proteins are anchored to their corresponding membrane via a single transmembrane segment (TMS) at their C-terminus. In yeast, the targeting of TA proteins to the endoplasmic reticulum (ER) can be mediated by the guided entry of TA proteins (GET) pathway, whereas it is not yet clear how mitochondrial TA proteins are targeted to their destination. It is widely observed that some mitochondrial outer membrane (OM) proteins are mistargeted to the ER when overexpressed or when their targeting signal is masked. However, the mechanism of this erroneous sorting is currently unknown. In this study, we demonstrate the involvement of the GET machinery in mistargeting of non-optimal mitochondrial OM proteins to the ER. These findings suggest that the GET machinery can, in principle, recognize and guide mitochondrial and non-canonical TA proteins. Hence, under normal conditions, an active mitochondrial targeting pathway must exist that dominates the kinetic competition against other pathways.
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Affiliation(s)
- Daniela G. Vitali
- Interfaculty Institute of Biochemistry, University of Tübingen, 72076 Tübingen, Germany
| | - Monika Sinzel
- Interfaculty Institute of Biochemistry, University of Tübingen, 72076 Tübingen, Germany
| | - Elianne P. Bulthuis
- Interfaculty Institute of Biochemistry, University of Tübingen, 72076 Tübingen, Germany
| | - Antonia Kolb
- Interfaculty Institute of Biochemistry, University of Tübingen, 72076 Tübingen, Germany
| | - Susanne Zabel
- Interfaculty Institute of Biochemistry, University of Tübingen, 72076 Tübingen, Germany
| | - Dietmar G. Mehlhorn
- Centre for Plant Molecular Biology, Developmental Genetics, University of Tübingen, Tübingen, Germany
| | | | - Ákos Farkas
- Department of Molecular Biology, Universitätsmedizin Göttingen, Göttingen 37073, Germany
| | - Anne Clancy
- Department of Molecular Biology, Universitätsmedizin Göttingen, Göttingen 37073, Germany
| | - Maya Schuldiner
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Christopher Grefen
- Centre for Plant Molecular Biology, Developmental Genetics, University of Tübingen, Tübingen, Germany
| | - Blanche Schwappach
- Department of Molecular Biology, Universitätsmedizin Göttingen, Göttingen 37073, Germany
| | - Nica Borgese
- Consiglio Nazionale delle Ricerche Institute of Neuroscience, Milan, Italy
| | - Doron Rapaport
- Interfaculty Institute of Biochemistry, University of Tübingen, 72076 Tübingen, Germany
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