We utilised molecular modelling to ascertain the location of the RGD motif in the structure of ACE2 to investigate the apparent functional redundancy of this motif in integrin binding. Examination of the ACE2 structure in silico [30] revealed that the motif was on the protein surface ( Figure 3A ). However, the space filling model revealed that the aspartate residue of the RGD motif faces into the active site cleft ( Figure 3B and 3C) and is, therefore, inaccessible for protein-protein interactions. The RSM sequence in tACE superimposes in exactly the same position as the RGD sequence in ACE2 and is therefore also inaccessible for proteinprotein interactions ( Figure 3D ). The similarity between the two proteins is illustrated by the close proximity of the outline trace and the degree of overlap. Variations in amino acid sequences are illustrated by the slight offset in the a-helical loops.