Abstract
BackgroundProtein secretion is a universal cellular process involving vesicles which bud and fuse between organelles to bring proteins to their final destination. Vesicle budding is mediated by protein coats; vesicle targeting and fusion depend on Rab GTPase, tethering factors and SNARE complexes. The Génolevures II sequencing project made available entire genome sequences of four hemiascomycetous yeasts, Yarrowia lipolytica, Debaryomyces hansenii, Kluyveromyces lactis and Candida glabrata. Y. lipolytica is a dimorphic yeast and has good capacities to secrete proteins. The translocation of nascent protein through the endoplasmic reticulum membrane was well studied in Y. lipolytica and is largely co-translational as in the mammalian protein secretion pathway.ResultsWe identified S. cerevisiae proteins involved in vesicular secretion and these protein sequences were used for the BLAST searches against Génolevures protein database (Y. lipolytica, C. glabrata, K. lactis and D. hansenii). These proteins are well conserved between these yeasts and Saccharomyces cerevisiae. We note several specificities of Y. lipolytica which may be related to its good protein secretion capacities and to its dimorphic aspect. An expansion of the Y. lipolytica Rab protein family was observed with autoBLAST and the Rab2- and Rab4-related members were identified with BLAST against NCBI protein database. An expansion of this family is also found in filamentous fungi and may reflect the greater complexity of the Y. lipolytica secretion pathway. The Rab4p-related protein may play a role in membrane recycling as rab4 deleted strain shows a modification of colony morphology, dimorphic transition and permeability. Similarly, we find three copies of the gene (SSO) encoding the plasma membrane SNARE protein. Quantification of the percentages of proteins with the greatest homology between S. cerevisiae, Y. lipolytica and animal homologues involved in vesicular transport shows that 40% of Y. lipolytica proteins are closer to animal ones, whereas they are only 13% in the case of S. cerevisiae.ConclusionThese results provide further support for the idea, previously noted about the endoplasmic reticulum translocation pathway, that Y. lipolytica is more representative of vesicular secretion of animals and other fungi than is S. cerevisiae.
Highlights
Protein secretion is a universal cellular process involving vesicles which bud and fuse between organelles to bring proteins to their final destination
Vesicle-mediated protein transport pathways The only membrane that a secretory protein must traverse is the membrane of the endoplasmic reticulum, the transport of the protein to its final destination continues through vesicles which bud and fuse between organelles [for reviews: [18,19]]
The sequencing of four hemiascomycetous yeasts has allowed us to search for proteins involved in vesicular transport by comparison with proteins identified in S. cerevisiae
Summary
Protein secretion is a universal cellular process involving vesicles which bud and fuse between organelles to bring proteins to their final destination. Y. lipolytica is a dimorphic yeast and has good capacities to secrete proteins. The translocation of nascent protein through the endoplasmic reticulum membrane was well studied in Y. lipolytica and is largely co-translational as in the mammalian protein secretion pathway. Its good protein secretion capacities have allowed the engineering of powerful heterologous protein expression systems [reviewed in [2]]. We focused on the early steps of protein translocation in the endoplasmic reticulum [4,5,6,7,8], on the quality control of protein folding [9] and on the glycosylation pathway [10]. Several genes involved in these steps were cloned and analysed
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