Is FURIN gene expression in salivary glands related to SARS-CoV-2 infectivity through saliva?

Unravelling the SARS-CoV- 2 mechanism of entry into host cells is engaging the endeavours of researchers worldwide and, although angiotensin-converting enzyme 2 (ACE2) is recognised as the primary receptor, many issues remain to be investigated.1 Remarkably, the interaction between ACE2 and the spike (S) glycosylated protein of SARS-CoV- 2 necessary for viral entry has been discovered by employing crystallography. S protein presents a receptor binding domain (RBD) and more specifically a receptor binding motif (RBM) which mediates the attachment to two virus-binding hotspots within ACE2 surface. The aminoacidic constitution of SARS-CoV- 2 RBM is highly homologous to that of SARS-CoV but shows some differences, specifically a four-residue motif at 482–485 (Gly-Val- Glu- Gly) that confers more affinity for ACE2 resulting in a tight relation between the two molecules.