Abstract
BackgroundProtein translocation across the membrane of the Endoplasmic Reticulum (ER) is the first step in the biogenesis of secretory and membrane proteins. Proteins enter the ER by the Sec61 translocon, a proteinaceous channel composed of three subunits, α, β and γ. While it is known that Sec61α forms the actual channel, the function of the other two subunits remains to be characterized.ResultsIn the present study we have investigated the function of Sec61β in Drosophila melanogaster. We describe its role in the plasma membrane traffic of Gurken, the ligand for the Epidermal Growth Factor (EGF) receptor in the oocyte. Germline clones of the mutant allele of Sec61β show normal translocation of Gurken into the ER and transport to the Golgi complex, but further traffic to the plasma membrane is impeded. The defect in plasma membrane traffic due to absence of Sec61β is specific for Gurken and is not due to a general trafficking defect.ConclusionBased on our study we conclude that Sec61β, which is part of the ER protein translocation channel affects a post-ER step during Gurken trafficking to the plasma membrane. We propose an additional role of Sec61β beyond protein translocation into the ER.
Highlights
Protein translocation across the membrane of the Endoplasmic Reticulum (ER) is the first step in the biogenesis of secretory and membrane proteins
In order to characterise the allele in greater detail we generated an antibody against the N-terminus of Sec61
Germline clones of sec61 P1 allele show reduced levels of Gurken protein at the plasma membrane of the oocyte Since the mRNA localization of Gurken was not affected by lack of Sec61, we investigated whether lack of Sec61 affects the translation of Gurken mRNA or events in the transport of Gurken protein to the plasma membrane
Summary
Protein translocation across the membrane of the Endoplasmic Reticulum (ER) is the first step in the biogenesis of secretory and membrane proteins. Proteins enter the ER by the Sec translocon, a proteinaceous channel composed of three subunits, , and. The nascent polypeptide chains of these proteins enter the ER via a proteinaceous channel called the Sec61p complex and gain access to the secretory pathway. If the mature protein does not possess specific signals for retention in the ER the protein exits the ER and is transported to the Golgi complex. From the trans-Golgi region the protein is either transported to endocytic organelles or to the plasma membrane. BMC Cell Biology 2009, 10:11 http://www.biomedcentral.com/1471-2121/10/11 in-vitro experiments using liposomes reconstituted with individual components of the Sec61p channel indicate that Sec and are necessary for the protein translocation per-se [2]. In accordance with the in-vitro data, in S. cerevisiae mutating and subunits of Sec61p is lethal whereas mutating Sec results only in a mild temperature sensitive phenotype [3,4]
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