Human coronaviruses (hCoVs) have
become a threat to global health
and society, as evident from the SARS outbreak in 2002 caused by SARS-CoV-1
and the most recent COVID-19 pandemic caused by SARS-CoV-2. Despite
a high sequence similarity between SARS-CoV-1 and -2, each strain
has a distinctive virulence. A better understanding of the basic molecular
mechanisms mediating changes in virulence is needed. Here, we profile
the virus-host protein–protein interactions of two hCoV nonstructural
proteins (nsps) that are critical for virus replication. We use tandem
mass tag-multiplexed quantitative proteomics to sensitively compare
and contrast the interactomes of nsp2 and nsp4 from three betacoronavirus
strains: SARS-CoV-1, SARS-CoV-2, and hCoV-OC43—an endemic strain
associated with the common cold. This approach enables the identification
of both unique and shared host cell protein binding partners and the
ability to further compare the enrichment of common interactions across
homologues from related strains. We identify common nsp2 interactors
involved in endoplasmic reticulum (ER) Ca
2+
signaling and
mitochondria biogenesis. We also identify nsp4 interactors unique
to each strain, such as E3 ubiquitin ligase complexes for SARS-CoV-1
and ER homeostasis factors for SARS-CoV-2. Common nsp4 interactors
include
N
-linked glycosylation machinery, unfolded
protein response associated proteins, and antiviral innate immune
signaling factors. Both nsp2 and nsp4 interactors are strongly enriched
in proteins localized at mitochondria-associated ER membranes suggesting
a new functional role for modulating host processes, such as calcium
homeostasis, at these organelle contact sites. Our results shed light
on the role these hCoV proteins play in the infection cycle, as well
as host factors that may mediate the divergent pathogenesis of OC43
from SARS strains. Our mass spectrometry workflow enables rapid and
robust comparisons of multiple bait proteins, which can be applied
to additional viral proteins. Furthermore, the identified common interactions
may present new targets for exploration by host-directed antiviral
therapeutics.