title: New insights into the targeting of a subset of tail-anchored proteins to the outer mitochondrial membrane.
abstract: Tail-anchored (TA) proteins are a unique class of functionally diverse membrane proteins defined by their single C-terminal membrane-spanning domain and their ability to insert post-translationally into specific organelles with an Ncytoplasm-Corganelle interior orientation. The molecular mechanisms by which TA proteins are sorted to the proper organelles are not well-understood. Herein we present results indicating that a dibasic targeting motif (i.e., -R-R/K/H-X({X≠E})) identified previously in the C terminus of the mitochondrial isoform of the TA protein cytochrome b 5, also exists in many other A. thaliana outer mitochondrial membrane (OMM)-TA proteins. This motif is conspicuously absent, however, in all but one of the TA protein subunits of the translocon at the outer membrane of mitochondria (TOM), suggesting that these two groups of proteins utilize distinct biogenetic pathways. Consistent with this premise, we show that the TA sequences of the dibasic-containing proteins are both necessary and sufficient for targeting to mitochondria, and are interchangeable, while the TA regions of TOM proteins lacking a dibasic motif are necessary, but not sufficient for localization, and cannot be functionally exchanged. We also present results from a comprehensive mutational analysis of the dibasic motif and surrounding sequences that not only greatly expands the functional definition and context-dependent properties of this targeting signal, but also led to the identification of other novel putative OMM-TA proteins. Collectively, these results provide important insight to the complexity of the targeting pathways involved in the biogenesis of OMM-TA proteins and help define a consensus targeting motif that is utilized by at least a subset of these proteins.
authors.affiliation: Department of Molecular and Cellular Biology, University of Guelph Guelph, ON, Canada.
authors.forename: Naomi J
authors.initials: NJ
authors.lastname: Marty
authors.affiliation: Department of Molecular and Cellular Biology, University of Guelph Guelph, ON, Canada.
authors.forename: Howard J
authors.initials: HJ
authors.lastname: Teresinski
authors.affiliation: Department of Molecular and Cellular Biology, University of Guelph Guelph, ON, Canada.
authors.forename: Yeen Ting
authors.initials: YT
authors.lastname: Hwang
authors.affiliation: Department of Molecular and Cellular Biology, University of Guelph Guelph, ON, Canada.
authors.forename: Eric A
authors.initials: EA
authors.lastname: Clendening
authors.affiliation: Department of Molecular and Cellular Biology, University of Guelph Guelph, ON, Canada.
authors.forename: Satinder K
authors.initials: SK
authors.lastname: Gidda
authors.affiliation: Department of Molecular and Cellular Biology, University of Guelph Guelph, ON, Canada ; Department of Plant Genetics, Physiology and Biotechnology, University of Technology and Life Sciences in Bydgoszcz Bydgoszcz, Poland.
authors.forename: Elwira
authors.initials: E
authors.lastname: Sliwinska
authors.affiliation: United States Department of Agriculture, Agricultural Research Service, US Arid-Land Agricultural Research Center Maricopa, AZ, USA.
authors.forename: Daiyuan
authors.initials: D
authors.lastname: Zhang
authors.affiliation: United States Department of Agriculture, Agricultural Research Service, Plant Genetics Research Unit, University of Missouri Columbia, MO, USA.
authors.forename: Ján A
authors.initials: JA
authors.lastname: Miernyk
authors.affiliation: Instituto do Cancer do Estado de Sao Paulo, Fundacao Faculdade de Medicina, Universidade de Sao Paulo Sao Paulo, Brazil.
authors.forename: Glauber C
authors.initials: GC
authors.lastname: Brito
authors.affiliation: Sunnybrook Research Institute and Department of Biochemistry, University of Toronto Toronto, ON, Canada.
authors.forename: David W
authors.initials: DW
authors.lastname: Andrews
authors.affiliation: United States Department of Agriculture, Agricultural Research Service, US Arid-Land Agricultural Research Center Maricopa, AZ, USA.
authors.forename: John M
authors.initials: JM
authors.lastname: Dyer
authors.affiliation: Department of Molecular and Cellular Biology, University of Guelph Guelph, ON, Canada.
authors.forename: Robert T
authors.initials: RT
authors.lastname: Mullen
keywords: A. thaliana; dibasic motif; mitochondria; outer mitochondrial membrane; tail anchored; targeting signal