The ER Protein Translocation Channel Subunit Sbh1 Controls Virulence of Cryptococcus neoformans.

Area of Science:

• Microbiology
• Molecular Biology
• Pathogenesis

Background:

• Cryptococcus neoformans possesses a critical polysaccharide capsule for virulence, with biogenesis dependent on the secretory pathway.
• Protein secretion involves translocation across the endoplasmic reticulum (ER) membrane via the conserved Sec61, Sbh1, and Sss1 channel.
• Sbh1, a divergent protein in the translocation channel, has phosphorylation sites suggesting regulatory roles in protein secretion.

Purpose of the Study:

• To investigate the role of Sbh1 in regulating protein secretion and its impact on Cryptococcus neoformans virulence.
• To determine if Sbh1 controls the entry of specific proteins into the secretory pathway, particularly under host-mimicking conditions.

Main Methods:

• Comparative analysis of wild-type and Δsbh1 mutant Cryptococcus neoformans strains.
• Proteomic analysis of protein secretion under conditions mimicking the mammalian host environment (tissue culture medium, 37°C, 5% CO2).
• Assessment of fungal cell-wall integrity and virulence in a mouse infection model.

Main Results:

• Absence of SBH1 leads to cell-wall defects in both C. neoformans and Saccharomyces cerevisiae.
• Proteomic analysis revealed that Sbh1 absence prevents the upregulation of specific secretory and transmembrane proteins under host-mimicking conditions.
• Sbh1-dependent proteins exhibit unique ER targeting sequences affecting their transit efficiency; many are involved in cell-wall biogenesis or are known virulence factors.
• The C. neoformans Δsbh1 mutant is avirulent in a mouse infection model.

Conclusions:

• Sbh1 is essential for controlling the entry of specific virulence factors into the secretory pathway of C. neoformans during host infection.
• Sbh1 regulates fungal pathogenicity by modulating the secretion of proteins critical for cell-wall integrity and virulence.
• The findings highlight Sbh1 as a key regulator of Cryptococcus neoformans pathogenesis, impacting virulence factor expression in response to host conditions.