The Vacuolar Morphogenesis Protein Vam6-Like Protein Vlp1 Is Required for Pathogenicity of Cryptococcus neoformans

Abstract

Cryptococcus neoformans is an encapsulated yeast pathogen that infects immunocompromised patients to cause fungal meningitis, resulting in hundreds of thousands of deaths each year. F-box protein Fbp1, the key component of the E3 ubiquitin ligase, plays a critical role in fungal development and virulence in fungal pathogens. In this study, we identified a potential substrate of Fbp1, the vacuolar morphogenesis protein Vam6-like protein Vlp1, and evaluated its role in virulence in C. neoformans. Deletion or overexpression of the VLP1 gene results in abnormal capsule formation and melanin production of C. neoformans. Stress tolerance assay showed that the vlp1Δ mutant was sensitive to SDS and NaCl but not to CFW or Congo red, indicating that Vlp1 might regulate the cell membrane integrity in C. neoformans. Fungal virulence assay showed that Vlp1 was essential for the pathogenicity of C. neoformans, as vlp1Δ mutants are avirulent in the mouse systematic infection model of cryptococcosis. The progression of fungal infection revealed that the vlp1Δ mutants were gradually eliminated from the lungs of the mice after infection. Moreover, the vlp1Δ mutants showed a proliferation defect inside macrophages and a viability defect in the host complement system, which likely contributes to the virulence attenuation of the vlp1Δ mutants. In summary, our results revealed that the vacuolar morphogenesis protein Vam6-like protein Vlp1 is essential for the pathogenicity of C. neoformans.

Vam6/Vps39/ TRAP1 ‐domain proteins influence vacuolar morphology, iron acquisition and virulence in Cryptococcus neoformans

“…Bar = 5 μm marked reduced capsule formation in defined LIM, indicating a distinct role. In general, our findings for the role of Vam6 are similar to those of Fan and Liu (2021) with regard to sensitivity to salt stress and capsule formation. The impact of the vam6Δ mutation on Rim101 trafficking may also be due to impaired acidification in endocytic compartments (Raymond et al, 1992;Solinger & Spang, 2013).…”

“…A further analysis using PANTHER classified the CNAG_07328 protein as vacuolar protein sorting-associated protein 3 with HMM E value score of 4.2e-258 indicating likely correct family assignment (Mi et al, 2021). An examination of the C. neoformans genome database revealed one other protein with a Vam6/Vps39/ TRAP1 domain (CNAG_05395); this protein was previously designated Vam6 or Vlp1 and was shown to contribute to C. neoformans pathogenesis (Fan & Liu, 2021;Lee et al, 2010;O. W. Liu et al, 2008;Tseng et al, 2012).…”

“…Here, we report that this approach identified a protein, Vps3, in the Vam6/Vps39/TRAP1 family that was distinct from a known member of this protein family in C. neoformans, the predicted HOPS complex protein Vam6/Vlp1. The latter protein was recently demonstrated to play a role in pathogenesis and the response to stress (Fan & Liu, 2021;Lee et al, 2010;O. W. Liu et al, 2008;Tseng et al, 2012).…”

More Than Just Cleaning: Ubiquitin-Mediated Proteolysis in Fungal Pathogenesis

“…The vaccine protection is effective even in mice depleted of CD4 + T cells, a condition mimics HIV/AIDS-induced immune deficiency ( Wang Y. et al., 2019 ). Several potential substrates of Fbp1 have been identified in C. neoformans ( Liu et al., 2011 ; Liu and Xue, 2014 ; Han et al., 2020 ; Fan and Liu, 2021 ). One of them, a Cdk-related kinase Crk1, has been found to be involved in meiosis regulation ( Liu et al., 2011 ; Liu and Shen, 2011 ).…”

“…Several additional Fbp1 interacting proteins, including mannoprotein Cmp1 and vacuolar morphogenesis protein Vlp1, has also been considered as potential substrates of Fbp1 based on protein pull-down assays, although their functional verification remains missing. Both proteins are required for pathogenicity of C. neoformans , as the vlp1 Δ mutant is avirulent and the cmp1 Δ mutant or the CMP1 overexpression strain shows virulence attenuation in a murine infection model of systemic cryptococcosis ( Han et al., 2020 ; Fan and Liu, 2021 ). Besides Fbp1, there are 19 additional F-box proteins in C. neoformans that remain to be studied.…”