Nicotinic receptors as SARS-CoV-2 spike co-receptors?

Abstract

Nicotinic acetylcholine receptors (nAChRs) play an important role in homeostasis and respiratory diseases. Controversies regarding the association between COVID-19 hospitalizations and smoking suggest that nAChRs may contribute to SARS-CoV-2 respiratory syndrome. We recently detailed the expression and localization of all nAChR subunits in the human lung. Since virus association with nAChRs has been shown in the past, we hypothesize that nAChR subunits act as SARS-CoV-2 Spike co-receptors. Based on sequence alignment analysis, we report domains of high molecular similarities in nAChRs with the binding domain of hACE2 for SARS-CoV-2 Spike protein. This hypothesis supported by in silico pilot data provides a rational for the modelling and the in vitro experimental validation of the interaction between SARS-CoV-2 and the nAChRs.

Keywords: ACE-2, Angiotensin converting enzyme-2; BR, Binding region; COVID-19; COVID-19, Coronavirus disease 2019; ETD, Extracellular topological domain; Lung; Nicotinic receptors; PDB, Protein data bank; RBD, Receptor binding domain; SARS-CoV-2; SARS-CoV-2, Severe acute respiratory syndrome coronavirus 2; hACE2; nAChRs, Nicotinic acetylcholine receptors; vdw, Van der Waals.

Fig. 1

hACE2 binding motifs to SARS-CoV-1 and 2 sequences. (A) Localizations of motifs 1 to 4 on hACE2 sequence (Q9BYF1) are highlighted in orange, blue, purple, and green respectively. Red residues are residues involved in van der Waals contact distance between hACE2 and SARS-CoV-1 and 2. Framed residues correspond to residues that are either interacting with SARS-CoV-2-RBD only (E35) or SARS-CoV-1-RBD only (Q325, E329). The residue highlighted in yellow corresponds to the 24th residue involved in van der Waals contact distance but not in the immediate proximity of other residues involved in the binding, therefore it was not included in the analysis. (B) The crystal structure (Protein Data Bank: 6M0J) shows the 4 motifs highlighted in (A) with similar colour codes. The crystal structure of SARS-CoV-2 spike receptor-binding domain bound with hACE2 (PDB ID: 6M0J [52]) was highlighted and exported from the viewer of the Research Collaboratory for Structural Bioinformatics (RCSB; www.rcsb.org).

Fig. 2

Clustal alignment of nAChRs with hACE2 binding motifs. Data from the UniProt Knowledgebase (UniProtKB, [53]) were used to perform a sequence alignment study of matching residues between hACE2/SARS-CoV-2 binding sites and nAChR protein sequences. The UniProtKB/Swiss-Prot accession numbers of the sequences used for analyzing the similarities are the following: ACE2 (Q9BYF1), CHRNA1 (P02708), CHRNA2 (Q15822), CHRNA3 (P32297), CHRNA4 (P43681), CHRNA5 (P30532), CHRNA6 (Q15825), CHRNA7 (P36544), CHRNA9 (Q9UGM1), CHRNA10 (Q9GZZ6), CHRNB1 (P11230), CHRNB2 (P17787), CHRNB3 (Q05901), CHRNB4 (P30926), CHRNG (P07510), CHRNE (Q04844), CHRND (Q07001). Motifs 1 to 4 were aligned with the 16 nAChR sequences to identify molecular similarities. The nAChR extracellular topological domains’ subunit sequences are represented with the partial alignment obtained with Clustal for the 4 motifs. *, position with a single fully conserved residue; :, position with a residue showing conservation between groups of strongly similar properties (scoring > 0.5 in the Gonnet PAM 250 matrix); ., position with a residue showing conservation between groups of weakly similar properties (scoring =<0.5 in the Gonnet PAM 250 matrix).