These differences depend on variances in the three-dimensional structure (3D) of the two enzymes. Comparative homology modeling and crystallography contributed to shed light on ACE2 3D structure (Figure 1). Prabakaran et al. (2004) clarified the major characteristic of ACE2, which is a deep channel on the summit of the protein, hosting the catalytic domain. Specific loops, like the long loop N210-Q221 that is exclusive of ACE2, α helices and a portion of β-sheet are located around the catalytic channel. The negative charge of the channel and the presence of distinct hydrophobic regions contribute to the specificity of the binding site (Prabakaran et al., 2004). The determination of the crystal structure of the extracellular domain to 2.2-3-A resolution from Towler et al. (2004) and the model from Guy et al. (2003) showed that the catalytic domain of ACE and ACE2 are very conserved and have similar mechanisms of action. The main difference stems from the smaller ACE2 pocket, thereby lodging only a single amino acid: the crucial substitution of the Gln281 in ACE binding pocket with Arg273 in ACE2 is likely to be responsible for the steric conflict (Guy et al., 2003; Towler et al., 2004). Another surprise of the ACE2 structure was its C-terminal domain, which—differently from ACE—revealed high homology with collectrin, a renal protein, which is involved in amino acids trafficking through the membrane (Yang et al., 2017).