The L. major virulence factor lipophosphoglycan defends against pore-forming toxins made by bacterial competitors, while the GP63 metalloproteinase activates pro-aerolysin like furin to protect L. major from aerolysin cytotoxicity.
ABSTRACT The pathogenic yeast Cryptococcus neoformans causes life-threatening meningoencephalitis in individuals with compromised immune systems. The ability of the fungus to cause disease depends on key cell-surface features, such as a polysaccharide capsule that protects it from the mammalian immune system. However, the mechanisms by which C. neoformans traffics polysaccharide capsule, melanin, and other materials to the cell surface are poorly understood. In this study, we employed mutants lacking specific subunits of the adaptor protein complex 1 (AP-1) to investigate its role in the elaboration of virulence-related materials at the cell surface. Importantly, the mutants displayed multiple defects, including alterations in capsule size and cell morphology, and defects in melanin production and urease secretion. Together, these results support the key observation that the AP-1 complex is required for C. neoformans survival in phagocytic cells. Together, our findings provide insights into the endomembrane trafficking machinery required for fungal pathogenesis.
Eddy Sánchez-León, Kabir Bhalla, Victoria French et al.· Infection and Immunity· 1 citation
ABSTRACT Cryptococcal meningoencephalitis is among the most prevalent invasive fungal diseases, posing a threat to immunocompromised individuals and representing a growing global health concern. The mechanisms of cryptococcal trafficking of virulence factors during disease are incompletely understood. Adaptor protein (AP) complexes play crucial roles in intracellular trafficking by orchestrating the sorting of macromolecular cargo and serving as essential components of the endocytic and secretory pathways. In a recent study, we demonstrated that Cryptococcus neoformans cells lacking the AP-1 complex subunits exhibit impaired elaboration of virulence factors and fail to survive in the harsh conditions of the macrophage phagolysosome. Although we characterized the phenotypes of AP-1 deficient cells in vitro, the contribution of this complex to pathogenesis remains unexplored. In this study, we show that mutants deficient in AP-1 complex subunits are either avirulent or exhibit attenuated virulence in a murine inhalational model. Loss of the small subunit resulted in the formation of granuloma-like lesions in mouse lungs with early containment of infection but eventual mortality, whereas mutants lacking the large subunits were rapidly cleared by mice. The delayed onset of disease in mice caused by mutants lacking the small subunit was marked by delayed weight loss and increased respiration rate, yet the mutant exhibited enhanced dissemination during late-stage infection, coinciding with waning immune responses and elevated collagen deposition. These findings demonstrate that deficiencies in the AP-1 complex impair C. neoformans virulence, reveal distinct roles for individual subunits, and identify the complex as a potential target for therapeutic intervention in cryptococcosis.
Kabir Bhalla, Eddy Sánchez-León, Yu-Hsuan Huang et al.· Infection and Immunity· 0 citations
TpeX is identified as a bactericidal, colicin-like pore-forming T6SS effector whose membrane activity is controlled by a cognate immunity protein, thereby expanding the repertoire of membrane-targeting weapons used by P. aeruginosa in interbacterial competition.
Chantal Soscia, Sébastien Reig, D. Lefebvre et al.· bioRxiv· 0 citations
The global rise of multidrug-resistant bacteria is a major health threat, with Klebsiella pneumoniae identified by the WHO as a critical priority pathogen. Phage-derived depolymerases have emerged as promising countermeasures because they can degrade the capsular polysaccharide (CPS) that shields bacteria from the immune system, thereby increasing their susceptibility to antibiotics and host defences. However, the limited understanding of how they recognise specific CPS structures remains a major obstacle to developing effective depolymerase-based therapeutics. In this study, we provide a comprehensive NMR and mutational analysis to characterise the mechanism of action of a miniaturised depolymerase, here mKP34gp57, targeting the clinically relevant K63 CPS. We show by NMR that mKP34gp57 hydrolyses CPS with high efficiency through an endoglycosidase-retaining mechanism. During substrate recognition, our data demonstrate that the enzyme interacts predominantly with the galactose and fucose moieties, which serve as the critical recognition features and thus the principal determinants of CPS specificity. Computational studies provide structural clues for the roles of the catalytic residues E266/E300 and D151. Finally, we prove that the hexasaccharide produced upon CPS hydrolysis stimulates dendritic cell maturation and T-helper-driven lymphocyte proliferation. Identifying the binding determinants that govern CPS recognition by mKP34gp57, and using this information to generate immunogenic fragments, deepens our understanding of how minidepolymerases can be rationally engineered to achieve tailored serotype specificity, and improved therapeutic and diagnostic potential.
Ferran Nieto-Fabregat, Mario Privitera, Angela Marseglia et al.· International Journal of Bio...· 0 citations
Unexpectedly, cytosolic extracts of both WT- and α”SLO-infected macrophages contained all histone proteins, suggesting that nucleosomal complexes are released into the cytosol during GAS infection.
Cheryl Y. M. Okumura, A. Quezada, Kevin Lord et al.· Journal of Immunology· 0 citations
Innate immune cells sense pathogenic bacteria like Legionella pneumophila through patterns such as the protein flagellin, a critical component of the bacterial motility apparatus. Recognition of cytosolic flagellin in mouse immune cells is well understood and mediated by the receptors, neuronal apoptosis inhibitory protein (Naip) 5 or Naip6, which activate the Nlrc4 inflammasome multi-protein complex for initiating cell death or interleukin-1 family cytokine release. However, the role of human NAIP as a cytosolic flagellin sensor remains controversial. Using a multipronged approach, we demonstrate that in a reconstituted cell system human NLRC4 engaged Legionella FlaA flagellin directly (i.e. without the need for hNAIP), whereas human NAIP did not interact with FlaA. Ectopic cytosolic FlaA expression also induced NLRC4 oligomerization, a prerequisite for inflammasome activation, in the absence of NAIP. Unexpectedly, the presence of NAIP diminished the binding of NLRC4 to flagellins and subsequent interleukin-1β release. Interestingly, in resting THP-1 cells, NAIP stably interacted with NLRC4, and during infection or stimulation with FlaA pro-inflammatory responses in THP-1 cells were predominantly NLRC4-dependent. Our data highlight NLRC4 as a putative direct sensor of cytosolic flagellins in the human system and NAIP as a potential negative regulator of flagellin sensing.
Gaopeng Li, Kenyatta Doumanas, Xiao Liu et al.· bioRxiv· 0 citations
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