A fluorescent peptide substrate facilitates investigation of ghrelin recognition and acylation by ghrelin O-acyltransferase

Ghrelin is a peptide hormone involved in regulation of appetite, glucose homeostasis, and a range of other physiological processes. Ghrelin requires a unique posttranslational modification, octanoylation of a serine side chain, to bind its cognate receptor to activate signaling. The enzyme that catalyzes this modification, ghrelin O-acyltransferase (GOAT), is receiving increased interest as a potential drug target for the treatment of obesity, diabetes, and other diseases proposed to be linked to ghrelin signaling. In this study, we report the development of a novel fluorescence-based assay for GOAT activity and the use of this assay to investigate GOAT inhibition and interactions underlying human GOAT (hGOAT) substrate selectivity. Using a series of mutations and chemical modifications of our fluorescent peptide substrate, we have identified specific groups on the first two amino acids of ghrelin that potentially contribute to ghrelin recognition by hGOAT. These data provide the first molecular-level information regarding interactions within the ghrelin–hGOAT complex. Defining the interactions used by hGOAT to bind and recognize ghrelin will provide insight into the structure of the hGOAT active site, aid in the design and optimization of targeted hGOAT inhibitors, and help to assess the possibility of novel hGOAT substrates beyond ghrelin.