Insulin degrading enzyme (IDE) is a protease which cleaves insulin and other bioactive peptides such as amyloid-β. Knock-out and genetic studies have linked IDE to Alzheimer's disease and type-2 diabetes. As the major insulin degrading protease, IDE is a candidate drug target in diabetes. Here we use kinetic Target-Guided Synthesis to design the first catalytic site inhibitor of IDE suitable for in vivo studies (BDM44768). Crystallographic and SAXS analyses shows that it locks IDE in a closed conformation. Amongst a panel of metalloproteases, BDM44768 selectively inhibits IDE. Acute treatment of mice with BDM44768 increases insulin signaling and surprisingly impairs glucose tolerance in an IDE-dependent manner. These results confirm that IDE is involved in pathways that modulate short-term glucose homeostasis, but casts doubt on the general usefulness of the inhibition of IDE catalytic activity to treat diabetes.

Insulin-degrading enzyme (IDE) selectively degrades the monomer of amyloidogenic peptides and contributes to clearance of amyloid β (Aβ). Thus, IDE retards the progression of Alzheimer's disease. IDE possesses an enclosed catalytic chamber that engulfs and degrades its peptide substrates; however, the molecular mechanism of IDE function, including substrate access to the chamber and recognition, remains elusive. Here, we captured a unique IDE conformation by using a synthetic antibody fragment as a crystallization chaperone. An unexpected displacement of a door subdomain creates an ∼18-Å opening to the chamber. This swinging-door mechanism permits the entry of short peptides into the catalytic chamber and disrupts the catalytic site within IDE door subdomain. Given the propensity of amyloidogenic peptides to convert into β-strands for their polymerization into amyloid fibrils, they also use such β-strands to stabilize the disrupted catalytic site resided at IDE door subdomain for their degradation by IDE. Thus, action of the swinging door allows IDE to recognize amyloidogenicity by substrate-induced stabilization of the IDE catalytic cleft. Small angle X-ray scattering (SAXS) analysis revealed that IDE exists as a mixture of closed and open states. These open states, which are distinct from the swinging door state, permit entry of larger substrates (e.g., Aβ, insulin) to the chamber and are preferred in solution. Mutational studies confirmed the critical roles of the door subdomain and hinge loop joining the N-and C-terminal halves of IDE for catalysis. Together, our data provide insights into the conformational changes of IDE that govern the selective destruction of amyloidogenic peptides.M16 metalloprotease | X-ray crystallography | substrate recognition P roteins in living organisms face acute and chronic challenges to their integrity, which necessitate proteostatic processes to protect their functions (1). Protein-protease networks play a key role in proteostasis by ensuring proper protein function through protein turnovers (2). Amyloidogenic peptides, such as amyloid β (Aβ) and amylin, present a major challenge to proteostasis, because they can form toxic aggregates that impair diverse physiological functions and contribute to human diseases (3, 4). Insulin-degrading enzyme (IDE), a Zn 2+ -metalloprotease, prefers to degrade amyloidogenic peptides to prevent the formation of amyloid fibrils (3). Exemplary substrates of IDE are insulin and Aβ, which are critical for the development of type 2 diabetes mellitus (DM2) and Alzheimer's disease (AD), respectively. Genetic analyses strongly support functional roles of IDE in the clearance of insulin and Aβ (2, 3). In humans, several single nucleotide polymorphisms at the IDE locus on human chromosome 10q are associated with DM2 and late-onset AD (5, 6).Structural analyses have provided significant insights to substrate recognition and catalysis by IDE. IDE has two ∼50-kDa αβαβα N-terminal (IDE-N) and C-terminal (IDE-C) halves, which are linked by a short hinge loop...

CC chemokine ligand 5 (CCL5) and CCL3 are critical for immune surveillance and inflammation. Consequently, they are linked to the pathogenesis of many inflammatory conditions and are therapeutic targets. Oligomerization and glycosaminoglycan (GAG) binding of CCL5 and CCL3 are vital for the functions of these chemokines. Our structural and biophysical analyses of human CCL5 reveal that CCL5 oligomerization is a polymerization process in which CCL5 forms rod-shaped, double-helical oligomers. This CCL5 structure explains mutational data and offers a unified mechanism for CCL3, CCL4, and CCL5 assembly into high-molecular-weight, polydisperse oligomers. A conserved, positively charged BBXB motif is key for the binding of CC chemokines to GAG. However, this motif is partially buried when CCL3, CCL4, and CCL5 are oligomerized; thus, the mechanism by which GAG binds these chemokine oligomers has been elusive. Our structures of GAG-bound CCL5 and CCL3 oligomers reveal that these chemokine oligomers have distinct GAG-binding mechanisms. The CCL5 oligomer uses another positively charged and fully exposed motif, KKWVR, in GAG binding. However, residues from two partially buried BBXB motifs along with other residues combine to form a GAG-binding groove in the CCL3 oligomer. The N termini of CC chemokines are shown to be involved in receptor binding and oligomerization. We also report an alternative CCL3 oligomer structure that reveals how conformational changes in CCL3 N termini profoundly alter its surface properties and dimer-dimer interactions to affect GAG binding and oligomerization. Such complexity in oligomerization and GAG binding enables intricate, physiologically relevant regulation of CC chemokine functions.signal transduction | CC chemokine | protein oligomerization | glycosaminoglycan | X-ray crystallography T he CC chemokines are a 28-member family of 8-to 14-kDa small-molecular-weight (MW) chemotactic cytokines with crucial roles in inflammation and infection (1, 2). Chemokine oligomerization and their interaction with glycosaminoglycans (GAGs), polysaccharides that are either free or attached to proteoglycans mostly on cell surface or in the extracellular matrix, is a coupled process that play key roles in chemokine functions (3-8). These include, but are not limited to, protection from proteolysis, regulation of chemotactic/haptatactic gradients to guide cell migration, transcytosis of chemokines across cells, and presentation to surface receptors of target cells, particularly under flow conditions. Most CC chemokines readily dimerize by themselves and form higher-MW complexes in the presence of GAGs (4). CC chemokine ligand 3 (CCL3) (MIP-1α), CCL4 (MIP-1β), and CCL5 (RANTES) are CCR5 ligands that are involved in diverse proinflammatory responses and are targeted for therapeutic innovations for human diseases including cancer, cardiovascular diseases, and HIV infection (9-12). Unlike other CC chemokines, these chemokines reversibly self-assemble into high-MW oligomers, up to >600 kDa in size (13,14). The pre...

Summary Human Presequence Protease (hPreP) is an M16 metalloprotease localized in mitochondria. There, hPreP facilitates proteostasis by utilizing a ∼13,300Å3 catalytic chamber to degrade a diverse array of potentially toxic peptides, including mitochondrial presequences and amyloid-β (Aβ), the latter of which contributes to Alzheimer's disease pathogenesis. Here we report crystal structures for hPreP alone and in complex with Aβ, which show that hPreP uses size-exclusion and charge complementation for substrate recognition. These structures also reveal hPreP-specific features that permit a diverse array of peptides, with distinct distributions of charged and hydrophobic residues, to be specifically captured, cleaved, and their amyloidogenic features destroyed. SAXS analysis demonstrates that hPreP in solution exists in dynamic equilibrium between closed and open states, with the former being preferred. Furthermore, Aβ binding induces the closed state and hPreP dimerization. Together, these data reveal the molecular basis for flexible yet specific substrate recognition and degradation by hPreP.