Contributions of human ACE2 and TMPRSS2 in determining host-pathogen interaction of COVID-19

Abstract

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection is at present an emerging global public health crisis. Angiotensin converting enzyme 2 (ACE2) and trans-membrane protease serine 2 (TMPRSS2) are the two major host factors that contribute to the virulence of SARS-CoV-2 and pathogenesis of coronavirus disease-19 (COVID-19). Transmission of SARS-CoV-2 from animal to human is considered a rare event that necessarily requires strong evolutionary adaptations. Till date no other human cellular receptors are identified beside ACE2 for SARS-CoV-2 entry inside the human cell. Proteolytic cleavage of viral spike (S)-protein and ACE2 by TMPRSS2 began the entire host-pathogen interaction initiated with the physical binding of ACE2 to S-protein. SARS-CoV-2 S-protein binds to ACE2 with much higher affinity and stability than that of SARS-CoVs. Molecular interactions between ACE2-S and TMPRSS2-S are crucial and preciously mediated by specific residues. Structural stability, binding affinity and level of expression of these three interacting proteins are key susceptibility factors for COVID-19. Specific protein-protein interactions (PPI) are being identified that explains uniqueness of SARS-CoV-2 infection. Amino acid substitutions due to naturally occurring genetic polymorphisms potentially alter these PPIs and poses further clinical heterogeneity of COVID-19. Repurposing of several phytochemicals and approved drugs against ACE2, TMPRSS2 and S-protein have been proposed that could inhibit PPI between them. We have also identified some novel lead phytochemicals present in Azadirachta indica and Aloe barbadensis which could be utilized for further in vitro and in vivo anti-COVID-19 drug discovery. Uncovering details of ACE2-S and TMPRSS2-S interactions would further contribute to future research on COVID-19.

Figure 1

Schematic diagram of SARS-CoV-2 viral particle and its genomic organization.

Figure 2

The phylogenetic analysis of the (a) whole genome of human coronaviruses (HCoV) with bat coronavirus (Bat-CoV-RaTG13); (b) S (spike) protein of HCoV with bat coronavirus (Bat-CoV-RaTG13). Virus species and sequence ids: HCoV-229E (NP_073551.1); HCoV-OC43 (YP_009555241.1); HCoV-NL63 (YP_003767.1); HCoV-HKU1 (YP_173238.1); SARS-CoV (NP_828851.1); MERS-CoV (YP_007188579.1); SARS-CoV-2 (YP_009724390.1); Bat-CoV-RaTG13 (EPI_ISL_402131).

Figure 3

Schematic diagram depicting the cellular entry and replication mechanism of SARS-CoV-2 in a human cell. SARS-CoV-2 enters cell through aerosol transmission and binds to ACE2 receptor (also present in bat and other species) which is widely present in alveolar cells of human lungs and fuses with membrane, this requires the two domains S1 and S2 of spike (S) protein to be cleaved using TMPRSS2 (serine protease). The positive sense single-stranded RNA (+ssRNA) genome translates two ORFs (1a and 1b) which can further transcribe and replicate into structural (S, M, E, N) and nonstructural proteins (NSPs). The virion proteins are translated and processed through rough endoplasmic reticulum (RER), Golgi and endoplasmic reticulum Golgi intermediate compartment (ERGIC) and inside endosomal vesicles they assemble and then through exocytosis the virocells are released. The viruses are ingested by antigen presenting cell (APCs) which presents viral S peptides to T helper cells which activates B cell and cytotoxic T cells.

Figure 4

Docking pose and surface structure of lead phytochemicals present in A. indica and A. barbadensis against Human TMPRSS2 proteins using molecular docking study. (a) Docking pose of lead phytochemicals at TMPRSS2 protein. (red, 10-hydroxyaloin A; cyan, CHEMBL518845; yellow, vepaol; green, nimbochalcin; megenta, melianin B; blue, camostat mesylate) (b) and (c) surface structure of A. barbadensis (10-hydroxyaloin A) and A. indica (nimbochalcin) phytochemical interacted with TMPRSS2 protein respectively. The lime green and orange colour in surface structure represents amino acids involved in hydrogen and hydrophobic bond formation, respectively. The selected phytochemical ligands for the study were downloaded from Indian Medicinal Plants, Phytochemistry and Therapeutics (IMPPAT) database (https://cb.imsc.res.in/imppat/basicsearch). The TMPRSS2 protein was modeled through Swiss-model server (https://swissmodel.expasy.org/). AutoDock and PyMol tools were used to perform the molecular docking study and visualization, respectively (Gupta et al. 2020a, b).

Figure 5.

In silico identification of human TMPRSS2 protein natural lead inhibitors present in A. indica and A. barbadensis.