Beta-Secretase (beta-SEC) is responsible for the intramembrane cleavage of amyloid precursor protein, an event intimately linked to Alzheimer's disease (AD). Beta-SEC is an aspartic protease composed by presenilin, nicastrin (NCT), APH-1, and PEN-2.Beta-SEC appears to have a very broad specificity; however, no quantitative data is available to support this assumption. NCT subunit is a type 1 membrane protein whose ectodomain (NCT ECD) actively participates in the substrate binding. NCT-substrate interaction is an essential step in the beta-SEC mechanism.The characterization of this interaction is important to better understand the secretase specificity, but also because it represents an attractive point for the design of inhibitors.The project objectives are: determine structure-functional relationships (SFRs) to reveal the key functionalities in the molecular structure of the substrates that are responsible for recognition by NCT and therefore for beta-SEC activity or inhibition; evaluate the contribution of NCT on the complex specificity; generate and evaluate a entirely new class of beta-SEC inhibitors.The NCT ECD is reminiscent of aminopeptidase structures and the NCT-E333 function suggests a common binding mechanism. Taking advantage of this similarity, we will build a model for the NCT ECD to define and explore a putative binding pocket.BIAcore technology and isotermal titration microcalorimetry will be used to characterize the interaction between NCT ECD (wt or mutant) and the substrate ectodomains.To gain further insight into which functional groups are significant for substrate recognition we will use a set of compounds to investigate the effects on constants affinities, with special interest in inhibitory activities.In conclusion, we will generate quantitative data about the specificity (related to NCT) of the beta-SEC. The experimentally determined SFRs will shed light on the possibility to design novel and more selective inhibitors for the AD's amyloid cascade.