The GPI anchor signal sequence dictates the folding and functionality of the Als5 adhesin from Candida albicans

Unveiling the structure of GPI-anchored protein of Malassezia globosa and its pathogenic role in pityriasis versicolor

Glycosylphosphatidylinositols (GPI)-anchored proteins (GpiPs) are related to the cell wall biogenesis, adhesion, interactions, protease activity, mating, etc. These proteins have been identified in many organisms, including fungi such as Neurospora crassa, Candida albicans, Saccharomyces cerevisiae, and Fusarium graminearum. MGL-3153 gene of Malassezia globosa (M. globosa) encodes a protein which is homologous of the M. restricta, M. sympodialis, M. Pachydermatis, and U. maydis GpiPs. Real-time PCR assay showed that the expression of MGL_3153 gene was significantly up-regulated among M. globosa isolated from patients with pityriasis versicolor (PV) compared to a healthy individual, suggesting the contribution of this gene in the virulence of M. globosa. Accordingly, the sequence of this protein was analyzed by bioinformatics tools to evaluate the structure of that. The conservation analysis of MGL-3153 protein showed that the C-terminal region of this protein, which is responsible for GPI-anchor ligation, was highly conserved during evolution while the N-terminal region just conserved in Malassezia species. Moreover, the predicted tertiary structure of this protein by homology modeling showed that this protein almost has alpha helix structure and represented a stable structure during 150 ns of molecular dynamic simulation. Our results revealed that this protein potentially belongs to GPI-anchored proteins and may contribute to the virulence of M. globosa which warrants further investigations in this area.

Saccharomyces cerevisiae Ras2 restores filamentation but cannot activate the first step of GPI anchor biosynthesis in Candida albicans

Ras proteins are highly conserved small GTPases in eukaryotes. GTP-bound Ras binds to effectors to trigger signaling cascades. In order to understand how extensive is the functional homology between the highly homologous proteins, S. cerevisiae Ras2 and C. albicans Ras1, we examined whether ScRas2 could functionally complement CaRas1 in activating hyphal morphogenesis as well as GPI anchor biosynthesis. We show that ScRas2 functionally complements CaRas1 in rescuing growth as well as activating hyphal growth, a process that involves plasma membrane localized Ras activating cAMP/PKA signaling via Cyr1. However, ScRas2 is unable to activate the GPI-N-acetylglucosaminyl transferase (GPI-GnT) which catalyzes the first step of GPI biosynthesis. That CaRas1 alone activates GPI-GnT and not ScRas2 suggests that this process is cAMP independent. Interestingly, CaRas1 transcriptionally activates CaGPI2, encoding a GPI-GnT subunit that has been shown to interact with CaRas1 physically. In turn, CaGPI2 downregulates CaGPI19, encoding another GPI-GnT subunit. This has direct consequences for expression of CaERG11, encoding the target of azole antifungals. This effect too is specific to CaRas1 and ScRas2 is unable to replicate it.

Ras signaling activates glycosylphosphatidylinositol (GPI) anchor biosynthesis via the GPI-N-acetylglucosaminyltransferase (GPI-GnT) in Candida albicans

The ability of Candida albicans to switch between yeast to hyphal form is a property that is primarily associated with the invasion and virulence of this human pathogenic fungus. Several glycosylphosphatidylinositol (GPI)-anchored proteins are expressed only during hyphal morphogenesis. One of the major pathways that controls hyphal morphogenesis is the Ras-signaling pathway. We examine the cross-talk between GPI anchor biosynthesis and Ras signaling in C. albicans. We show that the first step of GPI biosynthesis is activated by Ras in C. albicans This is diametrically opposite to what is reported in Saccharomyces cerevisiae Of the two C. albicans Ras proteins, CaRas1 alone activates GPI-GnT activity; activity is further stimulated by constitutively activated CaRas1. CaRas1 localized to the cytoplasm or endoplasmic reticulum (ER) is sufficient for GPI-GnT activation. Of the six subunits of the GPI-N-acetylglucosaminyltransferase (GPI-GnT) that catalyze the first step of GPI biosynthesis, CaGpi2 is the key player involved in activating Ras signaling and hyphal morphogenesis. Activation of Ras signaling is independent of the catalytic competence of GPI-GnT. This too is unlike what is observed in S. cerevisiae where multiple subunits were identified as inhibiting Ras2. Fluorescence resonance energy transfer (FRET) studies indicate a specific physical interaction between CaRas1 and CaGpi2 in the ER, which would explain the ability of CaRas1 to activate GPI-GnT. CaGpi2, in turn, promotes activation of the Ras-signaling pathway and hyphal morphogenesis. The Cagpi2 mutant is also more susceptible to macrophage-mediated killing, and macrophage cells show better survival when co-cultured with Cagpi2.

Fungal Biofilms: Inside Out

We focus this article on turning a biofilm inside out. The "inside" of the biofilm comprises the individual biofilm-related phenotypes, their environmental drivers and genetic determinants, and the coordination of gene functions through transcriptional regulators. Investigators have viewed the inside of the biofilm through diverse approaches, and this article will attempt to capture the essence of many. The ultimate goal is to connect the inside to the "outside," which we view as biofilm structure, development, pharmacological attributes, and medical impact.

Fungal Biofilms: Inside Out

We focus this article on turning a biofilm inside out. The "inside" of the biofilm comprises the individual biofilm-related phenotypes, their environmental drivers and genetic determinants, and the coordination of gene functions through transcriptional regulators. Investigators have viewed the inside of the biofilm through diverse approaches, and this article will attempt to capture the essence of many. The ultimate goal is to connect the inside to the "outside," which we view as biofilm structure, development, pharmacological attributes, and medical impact.

Peptide detection of fungal functional amyloids in infected tissue

Many fungal cell adhesion proteins form functional amyloid patches on the surface of adhering cells. The Candida albicansAgglutinin-like sequence (Als) adhesins are exemplars for this phenomenon, and have amyloid forming sequences that are conserved between family members. The Als5p amyloid sequence mediates amyloid fibril formation and is critical for cell adhesion and biofilm formation, and is also present in the related adhesins Als1p and Als3p. We have developed a fluorescent peptide probe containing the conserved Als amyloid-forming sequence. This peptide bound specifically to yeast expressing Als5p, but not to cells lacking the adhesin. The probe bound to both yeast and hyphal forms of C. albicans. Δals1/Δals3 single and double deletion strains exhibited reduced fluorescence, indicating that probe binding required expression of these proteins. Additionally, the Als peptide specifically stained fungal cells in abscesses in autopsy sections. Counterstaining with calcofluor white showed colocalization with the amyloid peptide. In addition, fungi in autopsy sections derived from the gastrointestinal tract showed colocalization of the amyloid-specific dye thioflavin T and the fluorescent peptide. Collectively, our data demonstrate that we can exploit amyloid sequence specificity for detection of functional amyloids in situ.