Experimental Active-Site Mapping by Fragments: Hot Spots Remote from the Catalytic Center of Endothiapepsin

Successful optimization of a given lead scaffold requires thorough binding-site mapping of the target protein particular in regions remote from the catalytic center where high conservation across protein families is given. We screened a 361-entry fragment library for binding to the aspartic protease endothiapepsin by crystallography. This enzyme is frequently used as a surrogate for the design of renin and β-secretase inhibitors. A hit rate of 20% was achieved, providing 71 crystal structures. Here, we discuss 45 binding poses of fragments accommodated in pockets remote from the catalytic dyad. Three major hot spots are discovered in remote binding areas: Asp81, Asp119, and Phe291. Compared to the dyad binders, bulkier fragments occupy these regions. Many of the discovered fragments suggest an optimization concept on how to grow them into larger ligands occupying adjacent binding pockets that will possibly endow them with the desired selectivity for one given member of a protein family.