Structure of the SARS-CoV-2 Orf3a - Human HMOX1 complex

Pull-down experiments show a strong interaction between orf3a and the host HMOX1 enzyme [PMID: 32511329]. As [32511329] discusses,  HMOX1 is an oxygenase that cleaves free heme. As such, it has a role in reducing oxidative stress, apoptosis, and specific cytokine signaling [29761622]. It is highly expressed in the lungs, and has been associated with a number of viral and bacterial infections [28566367, 29761622, 22490782]. There is a report that HMOX1 is upregulated in severe covid-19 cases compared with more moderate ones [32479746].

The structure of SARS2 Orf3a has recently been solved. The crystal structure is a dimer, with a helical membrane domain and globular domain. There is a report that the SARS-CoV-1 Orf3a forms a tetrameric ion channel [16894145]. Structures of HMOX1 are also available. Note that the HMOX1 structures do not include a membrane anchor sequence, that may be relevant to formation of the complex. The functional significance of Orf3a binding to HMOX1 is unknown. It is likely experimental work is in progress on the complex, but it is unknown when there may be a structure available. The challenges for the modeling community are first, is there convincing structural evidence of a specific physical interaction between these proteins; second, if so, what can be deduced about the functional significance of the interaction?