Recombination analysis on the receptor switching event of MERS-CoV and its close relatives: implications for the emergence of MERS-CoV

Background: PlMERS-CoV is a coronavirus known to cause severe disease in humans, taxonomically classified under the subgenus Merbecovirus. Recent findings showed that the close relatives of MERS-CoV infecting vespertillionid bats (family Vespertillionidae), named NeoCoV and PDF-2180, use their hosts’ ACE2 as their entry receptor, unlike the DPP4 receptor usage of MERS-CoV. Previous research suggests that this difference in receptor usage between these related viruses is a result of recombination. However, the precise location of the recombination breakpoints and the details of the recombination event leading to the change of receptor usage remain unclear. Methods: We used maximum likelihood-based phylogenetics and genetic similarity comparisons to characterise the evolutionary history of all complete Merbecovirus genome sequences. Recombination events were detected by multiple computational methods implemented in the recombination detection program. To verify the influence of recombination, we inferred the phylogenetic relation of the merbecovirus genomes excluding recombinant segments and that of the viruses’ receptor binding domains and examined the level of congruency between the phylogenies. Finally, the geographic distribution of the genomes was inspected to identify the possible location where the recombination event occurred. Results: Similarity plot analysis and the recombination-partitioned phylogenetic inference showed that MERS-CoV is highly similar to NeoCoV (and PDF-2180) across its whole genome except for the spike-encoding region. This is confirmed to be due to recombination by confidently detecting a recombination event between the proximal ancestor of MERS-CoV and a currently unsampled merbecovirus clade. Notably, the upstream recombination breakpoint was detected in the N-terminal domain and the downstream breakpoint at the S2 subunit of spike, indicating that the acquired recombined fragment includes the receptor-binding domain. A tanglegram comparison further confirmed that the receptor binding domain-encoding region of MERS-CoV was acquired via recombination. Geographic mapping analysis on sampling sites suggests the possibility that the recombination event occurred in Africa. Conclusion: Together, our results suggest that recombination can lead to receptor switching of merbecoviruses during circulation in bats. These results are useful for future epidemiological assessments and surveillance to understand the spillover risk of bat coronaviruses to the human population

Combining in vitro and in ovo assays to screen for anti-cancer and anti-angiogenic effects of the leaf extracts of Mallotus cumingii Müll.Arg. (Euphorbiaceae)

Cancer treatment is often challenging and various interventions may have detrimental effects. Due to this, the development of less harmful alternatives such as herbal medicine is essential. The present study aims to determine the leaf phytoconstituents present and the bioactivities of Mallotus cumingii Müll.Arg against cancer cells through the utilization of MTT assay and anti-angiogenesis through CAM assay. The leaf extracts obtained three fractions namely, methanolic crude (MCME) extracts, hexane extracts (MCHE), and ethyl acetate extracts (MCEA), and was tested on HCT-116 for in vitro cytotoxicity, and blood vessel density and branching through in ovo CAM assay. Phytochemical analysis showed that the M. cumingii fractions contain phenolic compounds, terpenoids, cardiac glycosides, flavonoids, and saponins. For in vitro set-up, MCME of M. cumingii were separated into MCHE and MCEA partitions and were tested against HCT-116 and obtained an IC50 value of < 30 μg/mL, which is deemed active in cytotoxicity. For in ovo set-up, two concentrations of each extract were applied to the duck eggs. Blood vessel density and number of branching points were measured through the ImageJ analysis. All extracts exhibited antiangiogenic activity, either by decreasing blood vessel density or the number of branching points. Overall, the study demonstrates the potential of M. cumingii as a source of therapeutic agents

Virological characteristics correlating with SARS-CoV-2 spike protein fusogenicity

IntroductionThe severe acute respiratory syndrome coronavirus (SARS-CoV-2) spike (S) protein is essential in mediating membrane fusion of the virus with the target cells. Several reports demonstrated that SARS-CoV-2 S protein fusogenicity is reportedly closely associated with the intrinsic pathogenicity of the virus determined using hamster models. However, the association between S protein fusogenicity and other virological parameters remains elusive.MethodsIn this study, we investigated the virological parameters (e.g., S1/S2 cleavage efficiency, plaque size, pseudoviral infectivity, pseudovirus entry efficiency, and viral replication kinetics) of eleven previous variants of concern (VOCs) and variants of interest (VOIs) correlating with S protein fusogenicity.Results and discussionS protein fusogenicity was found to be strongly correlated with S1/S2 cleavage efficiency and plaque size formed by clinical isolates. However, S protein fusogenicity was less associated with pseudoviral infectivity, pseudovirus entry efficiency, and viral replication kinetics. Taken together, our results suggest that S1/S2 cleavage efficiency and plaque size could be potential indicators to predict the intrinsic pathogenicity and S protein fusogenicity of newly emerged SARS-CoV-2 variants