Sergio A. Cadamuro

Macrocyclic statine-based inhibitors of BACE-1

Minimal sequence requirements for binding of substrate‐derived statine peptides to the aspartyl enzyme were established on the basis of the X‐ray cocrystal structure of the hydroxyethylene‐octapeptide OM00‐3 in complexation with BACE‐1. With this information to hand, macrocyclic compounds that conformationally restrict and preorganize the peptide backbone for an entropically favoured binding to the enzyme active site cleft were designed. By means of a side chain‐to‐side chain ring closure between two aspartyl residues in the P2 and P3′ positions through phenylene‐1,3‐dimethanamine, a 23‐membered ring structure was obtained; this structure retained an extended conformation of the peptide backbone, including the transition state analogue statine for tight interactions with the two aspartyl residues of the active centre. The conformational preorganization of the inhibitor molecule was verified by NMR structural analysis and was then confirmed by the crystal structure of the BACE‐1/inhibitor complex. Detailed insights into the binding mode of this macrocyclic inhibitor explained its moderate binding affinity in cell‐free assays (Ki=2.5 μM) and yielded precious information for possible structural optimization in view of the lack of steric clashes of the macrocycle with the flap domain of the enzyme.

Homotrimeric Collagen Peptides As Model Systems For Cell Adhesion Studies

Introduction Collagen model peptides with high triple-helix propensity can self-associate into the suprahelical structure, but folding/unfolding of such systems is strongly concentration-dependent. Cross-bridging of the three collagenous chains with synthetic templates as well as with native collagen-type or with artificial cystine knots has been successfully applied to overcome the shortcomings of self-assembled triple helices [1]. Aim of the present study was to analyze the conformational properties of a disulfide-crosslinked trimeric collagen model peptide (2 in Figure 1) containing the specific collagen type I motif recognized by the α1β1 and α2β1 integrins, i.e. the hexapeptide sequence portion GFOGER of the α1 chain [2]. Embedding this adhesion epitope into the triple helical collagenous peptide 3 (Figure 1) allowed X-ray structural analysis of the complex with the α2-I domain, which provides within the α2β1 integrin the principal binding site for collagen [3].