Use of an Intramolecular Quenched Fluorescence (IQF) Cleavage Assay for Assessing Enzyme Kinetics of Gamma-Secretase in Human Skin Fibroblasts and Keratinocytes

This study describes an intramolecular quenching assay to evaluate gamma-secretase (GS) enzyme activity in human dermal cells. The method utilizes a fluorogenic peptide substrate, mimicking a fragment of amyloid precursor protein (APP), in which a quencher suppresses the fluorescence of a fluorophore until enzymatic cleavage occurs, resulting in a measurable increase in fluorescence. This real-time, direct measurement of GS activity allows for precise kinetic analysis using Michaelis-Menten modeling to define Kd and Vmax. The assay is designed to quantify GS activity in human dermal fibroblasts and keratinocytes, enabling comparison between samples derived from hidradenitis suppurativa (HS) patients and healthy controls, as well as investigating the effects of subunit knockdown, such as nicastrin, on GS function. The method offers several advantages, including simplicity, cost-effectiveness, and adaptability for high-throughput screening for GS enzyme inhibitors.