Ghrelin proteolysis by insulin-degrading enzyme

Abstract

Here we report proteolysis of synthetic acylated human ghrelin by recombinant human insulin-degrading enzyme (IDE). Kinetic parameters and sites of proteolytic cleavage were evaluated. Ghrelin proteolysis by IDE was inhibited by ethylenediaminetetraacetate (EDTA), a metal chelating agent. Ghrelin proteolysis appears at least somewhat specific to M16 family proteases such as IDE, as the M13 protease neprilysin (NEP) did not exhibit ghrelin proteolysis in this study. A quenched fluorogenic peptide substrate comprising the primary sites of IDE-mediated ghrelin proteolysis (Mca-QRVQQRKESKK(Dnp)-OH; Mca: 7-methoxycoumarin-3-carboxylic acid; Dnp: 2,4-dinitrophenyl) was developed and used to evaluate enzyme specificity and kinetic parameters of proteolysis. Like acyl ghrelin, Mca-QRVQQRKESKK(Dnp)-OH was efficiently cleaved by IDE central to the target sequence. We anticipate that this quenched fluorogenic peptide substrate will be of value to future studies of ghrelin proteolysis by IDE and potentially other peptidases.