Human Recombinant Angiotensin-Converting Enzyme 2 (ACE2) Protein, aa18-740, is expressed in HEK293 cells. ACE2 activity results in vasodilation by degrading vasoconstrictor angiotensin II to produce vasodilator angiotensin. Decreased expression of this enzyme is associated with cardiovascular disease and possibly also glomerular injury in diabetic nephropathy. ACE2 contains a peptidase domain at the N-terminus and a single transmembrane helix. ACE2 is also the primary human receptor for the surface spike glycoprotein of SARS-CoV-2 and SARS-CoV. This receptor is expressed in human lung and small intestine epithelia as well as the heart, kidney, and testes. The peptidase domain of ACE2 binds to the protein-binding domain of the S1 protein subunit of the spike protein; this binding results in a cleavage site becoming exposed. Cleavage, or ‘protein priming’, is done by TMPRSS2, a cellular serine protease, and by cathepsins. This cleavage activates the S2 subunit of the spike protein, allowing the fusion of the viral membrane to the host cell membrane. At the carboxy terminus, Human Recombinant ACE2 Protein contains a TEV site and a human IgG1 Fc tag.