The functional importance of the N-terminal region of human prolylcarboxypeptidase

The renin-angiotensin-system cascade pathway generates the vasopressor and prothrombotic hormones, angiotensin II (Ang II) and angiotensin III (Ang III) from angiotensinogen. One of the key enzymes for the generation of angiotensin 1-7 (Ang 1-7) and angiotensin 2-7 (Ang 2-7) from Ang II and III, respectively, is prolylcarboxypeptidase (PRCP). To understand the contribution of the N-terminal region to catalysis, an N-terminal truncated form, lacking 179 N-terminal residues of PRCP (rPRCP40) was constructed. The circular dichroism (CD) spectrum of rPRCP40 illustrated that it was structured with significant helical content as indicated by local minima at ∼220 and 208 nm. The main products of Ang III metabolized by rPRCP40 were Ang 2-7 plus phenylalanine as determined by LC-MS. Angiotensin I (Ang I) blocked the metabolism of Ang III by rPRCP40. These investigations showed that the C-terminal region of the rPRCP40 contributes to PRCP's catalytic function, and provided additional experimental evidence for this suggestion.