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Title: New insights into the targeting of a sub-set of tail-anchored proteins to the outer mitochondrial membrane

item MARTY, NAOMI - University Of Guelph
item TERESINSKI, HOWARD J - University Of Guelph
item TING HWANG, YEEN - University Of Guelph
item CLENDENING, ERIC - University Of Guelph
item GIDDA, SATINDER - University Of Guelph
item ZHANG, DAIYUAN - Del Mar College
item Miernyk, Jan
item BRITO, GLAUBER - Universidad De Sao Paulo
item ANDREWS, DAVID - University Of Toronto
item Dyer, John
item MULLEN, ROBERT - University Of Guelph

Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/11/2014
Publication Date: 9/4/2014
Citation: Marty, N.J., Teresinski, H., Ting Hwang, Y., Clendening, E.A., Gidda, S.K., Zhang, D., Miernyk, J.A., Brito, G.C., Andrews, D.W., Dyer, J.M., Mullen, R.T. 2014. New insights into the targeting of a sub-set of tail-anchored proteins to the outer mitochondrial membrane. Frontiers in Plant Science. 5:426. doi: 10.3389/fpls.2014.00426.

Interpretive Summary: The agricultural yield of oilseed crops is largely determined by the efficient organization of the cellular contents of developing seeds. Individual parts must be made in the right place and at the right time to work effectively. After many years of study, most of the components that are necessary for oil production have been identified. There is, however, much less information about how and where the components are put together. In this study, scientists from the Agricultural Research Service in Columbia, MO, and Maricopa, AZ, in collaboration with scientists from other Institutes and Universities, identified and characterized the biochemical information, referred to as a “targeting motif,” that is responsible for organizing part of the cell. Using this information to search for the “targeting motif” in the genes of all other proteins in the reference plant Arabidopsis, some previously unknown components were identified. The results from this study greatly increase our understanding of how oil-related parts of cells are organized in seeds. This information will be of greatest interest to other scientists who study cellular organization in crop plants, and will help to identify specific targets for modification by both breeders and molecular biologists.

Technical Abstract: Tail-anchored (TA) proteins are a unique class of functionally diverse membrane proteins that are defined by their single C-terminal membrane-spanning domain and their ability to insert post-translationally into specific organelles with an Nout-Cin orientation. The molecular mechanisms by which TA proteins sort to the proper organelles, however, are not well understood. Here we present results indicating that a dibasic targeting signal 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 b5, also exists in many other outer mitochondrial membrane (OMM)-TA proteins in A. thaliana. 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 efficiently exchanged. We also present 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 allowed the identification of several other novel 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 define a consensus targeting signal motif that is utilized by at least a subset of these proteins.