Inactivation of Natriuretic Peptides by Human Insulin‐Degrading Enzyme Reveals New Insights on Substrate Recognition and Selectivity

Abstract

Atrial, brain, and C‐type natriuretic peptides (ANP, BNP, and CNP) are 3 physiological hormones that regulate blood pressure. Currently, all 3 natriuretic peptides are known to be cleared by 2 accepted processes: 1) receptor‐mediated internalization followed by lysosomal degradation; and 2) enzymatic degradation by neprilysin, a zinc‐dependent protease expressed on the plasma membrane. However, rat insulin‐degrading enzyme (IDE), also a zinc‐dependent protease, can also cleave rat natriuretic peptides. Here, we used human IDE to define the selectivity and sequence of cleavage events for the human natriuretic peptides and the role of IDE in their physiological clearance. Our studies reveal that ANP and CNP are preferred substrates over BNP. Analysis of the cleavage sites shows a preference for basic or hydrophobic residues on the N‐ or C‐terminal side of a peptide bond. In contrast to most of the known substrates of IDE, the cleavage events for natriuretic peptides suggest that their degradation is probabilistic and not sequential. For ANP and BNP, the 1st cleavage site by IDE occurs at the noncyclic portions of the peptides followed by cleavages in the 17‐member ring. Conversely, for CNP, the 1st cleavage by IDE can occur at the noncyclic portion or the 17‐member ring. Cellular studies using HEK‐293 cells show that the degradation of natriuretic peptides by IDE affect the natriuretic peptide‐induced cGMP levels.