Difference in the ACE2 utilization by SARS-CoV and SARS-CoV-2
We transfected the HeLa cells with the 20 plasmids expressing different
ACE2s individually or empty vector as a control. At 48 h post
transfection, the cells were infected with SARS-CoV-BJ01, SARS-CoV-2 or
Pangolin CoV pseudovirus. After 48 h of infection, the cells were lysed
and subjected to luciferase assay to evaluate the cell-entry efficiency
of the pseudoviruses mediated by different ACE2s. As shown inFigure 2 , little luminescence signals could be observed in
samples from HeLa cells transfected with empty vector and infected by
any of the three pseudoviruses, indicating that native HeLa without ACE2
could not mediate the pseudovirus entry. Luminescence signals from cells
expressing crucian, crocodile or viper snake ACE2 were also low,
indicating that fish and reptilian ACE2s could barely mediate the
pseudovirus entry. Cells expressing chicken or mouse ACE2 showed a
strong luminescence signal when infected by the SARS-CoV-BJ01
pseudovirus but not by the SARS-CoV-2 pseudovirus, indicating that
SARS-CoV-BJ01 could use chicken or mouse ACE2 for cell entry but
SARS-CoV-2 could not. Pangolin CoV was capable of utilizing both chicken
and mouse ACE2s, but its utilizing efficiency of chicken ACE2 was much
lower than SARS-CoV-BJ01. On the contrary, SARS-CoV-2 pseudovirus
ignited a stronger luminescence than SARS-CoV-BJ01 or Pangolin CoV
pseudovirus in cells expressing bat ACE2, indicating the highest
utilizing capability of bat ACE2 by SARS-CoV-2. For the other ACE2s,
infection of all the three pseudoviruses led to strong luminescence
signals, implying that all the three SARSr-CoV were capable of utilizing
a broad range of ACE2s.
A broad host range is supposed to lead to effective interspecies
transmission of virus and more potential to cause a pandemic. The
COVID-19 pandemic caused by SARS-CoV-2 is the most severe worldwide
pandemic in the recent years, surpassing the SARS pandemic in 2003, so
it is likely to speculate that SARS-CoV-2 has a broader host range.
Surprisingly, our cell-entry result showed that SARS-CoV-2 had a smaller
range of ACE2 utilization than SARS-CoV. SARS-CoV-2 could not utilize
mouse or chicken ACE2 which could be used by SARS-CoV, indicating a
narrower host range of SARS-CoV-2, especially in murine and birds. The
reason is probably that the host range of SARS-CoV-2 is broad enough to
support its transmission from bats to humans, and lack of infection to
some kinds of animals does not affect such transmission due to redundant
routes. Thus, it is not suggested to over-interpret the determination of
the host range on the possibility of a virus to cause pandemics,
especially for the viruses with broad host ranges.
Notably, SARS-CoV-2 has a better utilization of bat ACE2 than SARS-CoV.
Though SARS-CoV originate from bat-SARSr-CoV, the utilization of bat
ACE2 by SARS-CoV is quite limited which is supported by the previous
reports (Ren, Qu et al. 2008, Ge, Li et al. 2013). According our current
results, SARS-CoV-2 utilizes Chinese horseshoe bat ACE2 much better than
SARS-CoV, indicating a higher homology between SARS-CoV-2 and its
ancestor. This speculation is supported by the phylogenetic analysis of
viral genomes in the previous study (Zhou, Yang et al. 2020).
Our cell-entry result showed that SARS-CoV and SARS-CoV-2 could use a
wide variety of mammalian ACE2s, which is further supported by the
reports about the susceptibility of various mammals to SARS-CoV-2
infection (Shi, Wen et al. 2020). However, the utilization of fish and
reptilian ACE2s was quite poor for both SARS-CoV and SARS-CoV-2. This
can be explained by the remote phylogenetic relationship between
fish/reptilian ACE2s and mammalian ACE2s. By comparison, bird ACE2s have
closer phylogenetic relationship with mammalian ACE2s, and thus, bird
ACE2s could be used by some but not all SARSr-CoVs, such as SARS-CoV.
This indicates that SARSr-CoVs are more likely to be transmitted by
mammals and birds but not fish and reptiles, and more attention should
be paid to domestic mammals and birds to prevent CoV pandemic.