Characterizations of angiotensin-converting enzyme-2 (ACE2) peptidase activity

Angiotensin (Ang) II (1-8) is a potent vasoconstrictor known for its role in hypertension. Angiotensin-converting enzyme (ACE2) converts Ang II (1-8) to a vasodilator Ang (1-7) by removing the carboxy-terminal Phe. ACE2 more recently gained attention as the receptor for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that caused the coronavirus disease 2019 (COVID-19) pandemic. Given the pathophysiological importance of ACE2, the present study examined the mechanism of ACE2 catalytic activity by comparing the ability of angiotensin molecules of various lengths to compete with the artificial fluorogenic substrate. The Fluorimetric SensoLyte 390 ACE2 Activity Assay uses an Mca/Dnp fluorescence resonance energy transfer peptide as the substrate. Results showed that the natural substrate Ang II (1-8) competed with the fluorogenic substrate, reducing the fluorescence signals. Deletion of C-terminal Phe resulted in the loss of the ability to compete with the artificial substrate, as shown by the actions of Ang (1-7), Ang (2-7), and Ang (5-7). By contrast, the loss of N-terminal Asp potentiated the ability to compete with the substrate as seen by the action of Ang III (2-8). However, the loss of two amino acids (Asp-Arg) from the N-terminus reduced the ability to compete with the substrate as observed by the actions of Ang IV (3-8) and Ang (5-8). Ang I (1-10) and Ang (1-9) did not strongly compete with the substrate. Interestingly, shorter peptides Ang (1-5) and Ang (1-4) potentiated the ACE2 activity. These results suggest that Ang II and Ang III are the best natural substrates for ACE2.