A promising series of soluble γ-secretase modulators (SGSMs) has been discovered in our lab at UCSD in collaboration with MGH which inhibit the formation of the aggregation prone Aβ42 peptide in favor of shorter less pathogenic Aβ isoforms. Despite the development of numerous potent SGSMs, the molecular target and the mechanism of action remain unknown. We propose the synthesis of three distinct clickable SGSM-photoprobes for cross-linking studies to demonstrate the binding site of these ligands within the γ-secretase enzyme. Additional experiments will be conducted using novel Aβ substrates in order to evaluate the mechanism by which SGSMs affect the processivity of γ-secretase. This research will identify the critical sites of interaction between the SGSMs and their molecular target, as well as provide valuable information toward the development of more potent and selective compounds. In addition, evaluating the processivity of γ-secretase will enable a critical understanding of the mechanism by which the SGSMs selectively attenuate the production of the pathogenic Aβ42 peptide and enrich our fundamental understanding of this enigmatic enzyme. A subset of these studies will directly test the processivity model of γ-secretase activity. Collectively, these studies serve to identify the target and mode of action of our novel SGSMs with the goal of discovering potential therapeutic agents for the treatment of Alzheimer’s disease (AD).