[초청강연] Biogenesis of secretory and membrane proteins in the eukaryotic cell

Approximately 30-40% of the eukaryotic proteome are localized in subcellular
organelles of the secretory pathway or secreted. It has been thought that protein targeting
and translocation to the endoplasmic reticulum (ER) occur via two distinct pathways: signal
recognition particle (SRP) dependent co-translational or SRP independent, Sec62/Sec63
dependent post-translational translocation pathway. However, recent studies suggest that
the ER protein targeting and the Sec62/Sec63 dependent translocation are more intricate
than earlier thought. Current understanding of the roles of the Sec62/Sec63 complex-
mediated translocation and membrane insertion of proteins in the ER will be discussed. The
ER-targeted proteins contain a signal sequence (SS) which functions in opening of the
translocation channel. Some SSs are cleaved by signal peptidase while others are not and
become membrane anchored. Underlying mechanisms of how signal peptidase selects
substrates remain elusive. Our recent data suggest the involvement of Spc1/Spc2, non-
catalytic subunits of the signal peptidase complex in these processes. Implication of our data
and possible mechanisms of signal peptidase will be discussed.