Functional analysis of the Sec62 C-terminal domain in membrane protein biogenesis

Abstract

About 30 % of proteome in yeast are targeted to the endoplasmic reticulum (ER) membrane either by the signal recognition particle (SRP)-dependent pathway or the SRP-independent pathway. In the SRP-independent pathway, an essential protein Sec62p cooperates with Sec61p, a main protein conducting channel for the ER targeted membrane and secretory proteins. However, the molecular mechanism of Sec62p in this process has not been elucidated in detail. The cytosolic C-terminal domain of Sec62p has been proposed as an acceptor site for N-terminal signal sequences of secretory proteins. To further study the role of the C-terminus of Sec62p in membrane protein biogenesis, C-terminal mutants of Sec62p were prepared and the membrane insertion of model membrane proteins was examined. We found that P219A mutation reduced the C-terminal translocation of model membrane proteins, suggesting that the C-terminus of Sec62p may function on the insertion of membrane proteins into the ER membrane. In addition, we probe for the site of physical interaction between Sec62p and the substrate proteins using a site-specific cross-linking approach.