Porcine Deltacoronavirus Utilizes Sialic Acid as an Attachment Receptor and Trypsin Can Influence the Binding Activity

Abstract

Porcine deltacoronavirus (PDCoV) is a novel coronavirus that causes diarrhea in nursing piglets. Studies showed that PDCoV uses porcine aminopeptidase N (pAPN) as an entry receptor, but the infection of pAPN-knockout cells or pigs with PDCoV revealed that pAPN might be not a critical functional receptor, implying there exists an unidentified receptor involved in PDCoV infection. Herein, we report that sialic acid (SA) can act as an attachment receptor for PDCoV invasion and facilitate its infection. We first demonstrated that the carbohydrates destroyed on the cell membrane using NaIO4 can alleviate the susceptibility of cells to PDCoV. Further study showed that the removal of SA, a typical cell-surface carbohydrate, could influence the PDCoV infectivity to the cells significantly, suggesting that SA was involved in the infection. The results of plaque assay and Western blotting revealed that SA promoted PDCoV infection by increasing the number of viruses binding to SA on the cell surface during the adsorption phase, which was also confirmed by atomic force microscopy at the microscopic level. In in vivo experiments, we found that the distribution levels of PDCoV and SA were closely relevant in the swine intestine, which contains huge amount of trypsin. We further confirmed that SA-binding capacity to PDCoV is related to the pre-treatment of PDCoV with trypsin. In conclusion, SA is a novel attachment receptor for PDCoV infection to enhance its attachment to cells, which is dependent on the pre-treatment of trypsin on PDCoV. This study paves the way for dissecting the mechanisms of PDCoV–host interactions and provides new strategies to control PDCoV infection.

Exploration of PDCoV-induced apoptosis through mitochondrial dynamics imbalance and the antagonistic effect of SeNPs

“…Trypsin has been demonstrated to increase viral infectivity in cells ( 36 ). In a similar vein, after 24 h of incubation on ST cells without trypsin, no cells were infected with PDCoV by immunofluorescence, and when 4 μg/mL of trypsin was added, virus replication increased 70.4 times that of the non-addition group, which could be because trypsin promotes PDCoV attachment to cells ( 37 ) cleaving and activating the PDCoV S protein, allowing the virus to enter cells ( 38 ). Trypsin has also been proposed to promote viral replication by provoking the fusion of infected cells’ intercellular membranes ( 39 ).…”

Porcine Deltacoronaviruses: Origin, Evolution, Cross-Species Transmission and Zoonotic Potential

“…Furthermore, CD163 and pAPN double-gene-knockout pigs exhibited decreased susceptibility to PDCoV [92]. A recent study reported that sialic acids serve as a binding receptor of PDCoV [93]; however, whether sialic acids are PDCoV receptors or just attachment factors is still unknown. Additionally, lung fibroblast-like cells, derived from the pAPN knockout porcine alveolar macrophage (PAM) cultures, still supported PDCoV replication to high levels [94].…”

Swine Enteric Coronavirus: Diverse Pathogen–Host Interactions

“…SA can promote the adhesion ability of PDCoV, relating to the intestinal tissue tropism of PDCoV. These results suggest that SA may be a cofactor of PDCoV infection [ 71 ].…”

“…As an extracellular protease, trypsin activates the PDCoV S protein to induce intercellular fusion. Trypsin is needed in the culture and passage of SeCoV, which promotes the fusion of virus and cells and increases the yield of virus [ 71 , 77 , 78 , 79 ] ( Figure 3 ).…”