Download Different sorting of nearly similar membrane proteins to the plasma

Different sorting of nearly similar membrane proteins to the plasma membrane and to the mitochondria membrane Charlotte von Chappuis1, Jörg Balss1, Tobias Meckel1, Anna Moroni2, Gerhard Thiel1 1
Inst. Botany, Technische Universität Darmstadt, Schnittspahnstrasse 3, D-­‐64287 Darmstadt, Germany, Department of Biology and CNR Istitutio di Biofisica, Università degli Studi di Milano, Via Celoria 26, 20133 Milano, Italy 2
K+ channels can be found in the plasma membrane but also in the membrane of organelles such as mitochondria.The mechanism of protein synthesis and the targeting of these similar K+ channel proteins to the different sites of action are mostly unknown. The general believe is that membrane proteins are synthesized in a co-­‐translational manner for sorting to the plasma membrane and that the membrane proteins of mitochondria are sorted in a posttranslational manner.I am trying to understand the pathways and the mechanism of sorting of similar membrane proteins to the plasma membrane and into the mitochondria membrane. The tools are two small and very similar viral K+ channels. One of these channels, Kcv from virus PBCV1 can be expressed heterologously in several systems including mammalian cells, xenoupusoocytes and yeast. In these cells the channel is sorted into the secretory pathway and finally to the plasma membrane where its activity can be measured. The second channel, Kesv from virus ESV-­‐1, is structurally very similar to Kcv. Nonetheless its sorting is entirely different; the protein Kesv is imported in a voltage dependent manner via the canonical TOM/TIM complex into the mitochondria (Balss et al. 2008). A pathway for the differential sorting could be provided by the mitochondria associated membranes (MAMs). These sub domains of the endoplasmatic reticulum (ER) are in a direct physical contact with the mitochondria. MAMs can act as a sorting station for proteins from the ER both into the secretory pathway (SP) and the mitochondria. The viral membrane protein “UL37 exon 1 protein” (pUL37x1) from the human cytomegalovirus for example is sorted in this manner (Bozidis et.al; 2007). Analysis of confocal images with specific labeled MAMs and RFP labeled Kesv in HEK293 cells show that the channel is not sorted via MAMs to the mitochondria. Currently I am creating chimeras of both K+channels and follow their sorting. The general message is that Kesv can be easily redirected from the mitochondria to the secretory pathway only by exchanging parts of TMD1 of Kesv with that of Kcv. A titration of the TMD length required for this switch in sorting shows that the downstream half of TMD1 from Kcv is sufficient as a targeting signal into the SP. Jörg Balss, Panagiotis Papatheodorou, Mario Mehmel, Dirk Baumeister, Brigitte Hertel, Nicolas Delaroque, Franck C. Chatelain, Daniel L. Minor, Jr., James L. Van Etten, Joachim Rassow, Anna Moroni, and Gerhard Thiel +
(2008):Transmembranedomain length of viral K channels is a signal for mitochondria targeting doi:10.1073/pnas.0805709105 PetrosBozidis, Chad D. Williamson, and Anamaris M. Colberg-­‐Poley (2007):Mitochondrial and secretory human cytomegalovirus UL37 proteins traffic into mitochondrion-­‐associated membranes of human cells doi:10.1128/JVI.02456-­‐07