An Aerolysin-like Pore-Forming Protein Complex Targets Viral Envelope to Inactivate Herpes Simplex Virus Type 1

Abstract

Because most of animal viruses are enveloped, cytoplasmic entry of these viruses via fusion with cellular membrane initiates their invasion. However, the strategies in which host cells counteract cytoplasmic entry of such viruses are incompletely understood. Pore-forming toxin aerolysin-like proteins (ALPs) exist throughout the animal kingdom, but their functions are mostly unknown. In this study, we report that bg-crystallin fused aerolysin-like protein and trefoil factor complex (bg-CAT), an ALP and trefoil factor complex from the frog Bombina maxima, directly blocks enveloped virus invasion by interfering with cytoplasmic entry. bg-CAT targeted acidic glycosphingolipids on the HSV type 1 (HSV-1) envelope to induce pore formation, as indicated by the oligomer formation of protein and potassium and calcium ion efflux. Meanwhile, bg-CAT formed ring-like oligomers of ~10 nm in diameter on the liposomes and induced dye release from liposomes that mimic viral envelope. Unexpectedly, transmission electron microscopy analysis showed that the bg-CATtreated HSV-1 was visibly as intact as the vehicle-treated HSV-1, indicating that bg-CAT did not lyse the viral envelope. However, the cytoplasmic entry of the bg-CATtreated HSV-1 into HeLa cells was totally hindered. In vivo, topical application of bg-CAT attenuated the HSV-1 corneal infection in mice. Collectively, these results uncovered that bg-CAT possesses the capacity to counteract enveloped virus invasion with its featured antiviral-acting manner. Our findings will also largely help to illustrate the putative antiviral activity of animal ALPs.

Pore-forming protein βγ-CAT promptly responses to fasting with capacity to deliver macromolecular nutrients

“…This phenomenon was also observed in βγ-CAT-mediated water maintaining in toad urinary bladders (Zhao et al, 2021). βγ-CAT is a PFP protein, and it forms membrane channels with a preference for cations, including Na + , K + , and Ca 2+ (Liu et al, 2021; Zhao et al, 2021). The presence of βγ-CAT channels in endolysosomes leads to a rapid flux of Na + (Zhao et al, 2021).…”

“…BmALP1 interacts with the trefoil factor (TFF) BmTFF3 to form a βγ-crystallin-fused af-PFP and TFF complex, named βγ-CAT for its domain composition. This protein complex can form membrane pores (channels) with a functional diameter of approximately 1.5-2.0 nm (Liu et al, 2008;Liu et al, 2021).…”

“…The complex acts on endocytic and exocytic systems to form channels in endolysosomes, which promotes cell material import and export through endolysosomal pathways (Zhang et al, 2021). These cellular effects have been shown to be involved in immune defense and tissue repair (Xiang et al, 2014;Li et al, 2017;Gao et al, 2019;Deng et al, 2020;Liu et al, 2021) as well as in toad water maintaining by driving macropinocytosis under osmotic stress (Zhao et al, 2021).…”

“…BmALP1 interacts with the trefoil factor (TFF) BmTFF3 to form a βγ-crystallin-fused af-PFP and TFF complex, named βγ-CAT for its domain composition. This protein complex can form membrane pores (channels) with a functional diameter of approximately 1.5–2.0 nm (Liu et al, 2008; Liu et al, 2021). BmALP3, a paralog of BmALP1, lacks the membrane pore-forming capacity, but it acts as a negative regulator of the assembly of the βγ-CAT complex via redox changes depending on environmental cues (Wang et al, 2020).…”

“…The complex acts on endocytic and exocytic systems to form channels in endolysosomes, which promotes cell material import and export through endolysosomal pathways (Zhang et al, 2021). These cellular effects have been shown to be involved in immune defense and tissue repair (Xiang et al, 2014; Li et al, 2017; Gao et al, 2019; Deng et al, 2020; Liu et al, 2021) as well as in toad water maintaining by driving macropinocytosis under osmotic stress (Zhao et al, 2021). Acting as a secretory endolysosome channel (SELC) protein, βγ-CAT and its regulatory network (βγ-CAT-pathway) act as a novel PFP-mediated cell vesicular delivery and transport system, playing multiple roles in the adaptation of toads to diverse environmental conditions (Zhang et al, 2021).…”