ACE2 is a multiform protein (Feng et al., 2010, 2011). As discussed above (section Structure of ACE2) its C-terminal domain is similar to collectrin, a kidney protein involved in amino acids trafficking and insulin secretion (Kuba et al., 2013). Alterations in ACE2 have been demonstrated in Hartnup’s disease due to a disturbance in amino acids homeostasis. Indeed, ACE2 has been proposed to modulate amino acid transport in bowel and gut microbiome (Hashimoto et al., 2012).