Deletion analysis of yeast Sec65p reveals a central domain that is sufficient for function in vivo

The Role of Secretory Pathways in Candida albicans Pathogenesis

Candida albicans is a fungus that is a commensal organism and a member of the normal human microbiota. It has the ability to transition into an opportunistic invasive pathogen. Attributes that support pathogenesis include secretion of virulence-associated proteins, hyphal formation, and biofilm formation. These processes are supported by secretion, as defined in the broad context of membrane trafficking. In this review, we examine the role of secretory pathways in Candida virulence, with a focus on the model opportunistic fungal pathogen, Candida albicans.

The Candida albicans Kar2 protein is essential and functions during the translocation of proteins into the endoplasmic reticulum

Since the secretory pathway is essential for Candida albicans to transition from a commensal organism to a pathogen, an understanding of how this pathway functions may be beneficial for identifying novel drug targets to prevent candidiasis. We have cloned the C. albicans KAR2 gene, which performs many roles during the translocation of proteins into the endoplasmic reticulum (ER) during the first committed step of the secretory pathway in many eukaryotes. Our results show that C. albicans KAR2 is essential, and that the encoded protein rescues a temperature-sensitive growth defect found in a Saccharomyces cerevisiae strain harboring a mutant form of the Kar2 protein. Additionally, S. cerevisiae containing CaKAR2 as the sole copy of this essential gene are viable, and ER microsomes prepared from this strain exhibit wild-type levels of post-translational translocation during in vitro translocation assays. Finally, ER microsomes isolated from a C. albicans strain expressing reduced amounts of KAR2 mRNA are defective for in vitro translocation of a secreted substrate protein, establishing a new method to study ER translocation in this organism. Together, these results suggest that C. albicans Kar2p functions during the translocation of proteins into the ER during the first step of the secretory pathway.

Protein A-tagging for purification of native macromolecular complexes from Candida albicans

Protein A-tagging has become an important tool in characterization of protein-protein interactions in many systems, allowing purification of multicomponent complexes under native conditions. Here we provide a set of vectors that allow protein A-tagging in Candida albicans, through addition of the tag to open reading frames. These vectors were successfully used to generate stably tagged proteins that were functional, shown to be localized appropriately or assembled into complexes. These new vectors comprise a useful addition to the C. albicans molecular toolbox.

The URA5 gene encoding orotate-phosphoribosyl transferase of the yeast Kluyveromyces lactis: cloning, sequencing and use as a selectable marker

A pair of degenerate primers was used for amplification and cloning of an internal fragment of the K. lactis URA5 gene. Primers were designed on the basis of highly conserved motifs within protein sequences predicted for URA5 genes from several microorganisms. Using the amplified fragment as a probe, we finally cloned and sequenced a 1.9 kb chromosomal fragment containing the orotate-phosphoribosyltransferase-encoding URA5 gene and an incomplete open reading frame strikingly similar to SEC65 of Saccharomyces cerevisiae and other yeasts, in which the gene encodes a subunit of the signal recognition particle. Uracil-requiring mutants of K. lactis CBS 683 were selected on media containing 5-fluoro-orotic acid and used as recipients in transformation experiments using K. lactis URA5 as the selectable marker, thereby proving functionality of the cloned gene.