The membrane-bound glycoprotein dipeptidyl peptidase IV (DP IV, CD26) is a unique multifunctional protein, acting as receptor, binding and proteolytic molecule. We have determined the sequence and 1.8 Å crystal structure of native DP IV prepared from porcine kidney. The crystal structure reveals a 2-2-2 symmetric tetrameric assembly which depends on the natively glycosylated ␤-propeller blade IV. The crystal structure indicates that tetramerization of DP IV is a key mechanism to regulate its interaction with other components. Each subunit comprises two structural domains, the N-terminal eight-bladed ␤-propeller with open Velcro topology and the C-terminal ␣͞␤-hydrolase domain. Analogy with the structurally related POP and tricorn protease suggests that substrates access the buried active site through the ␤-propeller tunnel while products leave the active site through a separate side exit. A dipeptide mimicking inhibitor complexed to the active site discloses key determinants for substrate recognition, including a Glu-Glu motif that distinguishes DP IV as an aminopeptidase and an oxyanion trap that binds and activates the P 2-carbonyl oxygen necessary for efficient postproline cleavage. We discuss active and nonactive site-directed inhibition strategies of this pharmaceutical target protein.serine protease ͉ oxyanion hole ͉ substrate channeling ͉ drug design ͉ diabetes mellitus

Acute and chronic inflammatory disorders are characterized by detrimental cytokine and chemokine expression. Frequently, the chemotactic activity of cytokines depends on a modified N-terminus of the polypeptide. Among those, the N-terminus of monocyte chemoattractant protein 1 (CCL2 and MCP-1) is modified to a pyroglutamate (pE-) residue protecting against degradation in vivo. Here, we show that the N-terminal pE-formation depends on glutaminyl cyclase activity. The pE-residue increases stability against N-terminal degradation by aminopeptidases and improves receptor activation and signal transduction in vitro. Genetic ablation of the glutaminyl cyclase iso-enzymes QC (QPCT) or isoQC (QPCTL) revealed a major role of isoQC for pE1-CCL2 formation and monocyte infiltration. Consistently, administration of QC-inhibitors in inflammatory models, such as thioglycollate-induced peritonitis reduced monocyte infiltration. The pharmacologic efficacy of QC/isoQC-inhibition was assessed in accelerated atherosclerosis in ApoE3*Leiden mice, showing attenuated atherosclerotic pathology following chronic oral treatment. Current strategies targeting CCL2 are mainly based on antibodies or spiegelmers. The application of small, orally available inhibitors of glutaminyl cyclases represents an alternative therapeutic strategy to treat CCL2-driven disorders such as atherosclerosis/restenosis and fibrosis.

The incretins glucose-dependent insulinotropic polypeptide (GIP 1-42 ) and glucagon-like peptide-1-(7-36)-amide (GLP-1 7-36 ), hormones that potentiate glucose-induced insulin secretion from the endocrine pancreas, are substrates of the circulating exopeptidase dipeptidyl peptidase IV and are rendered biologically inactive upon cleavage of their N-terminal dipeptides. This study was designed to determine if matrix-assisted laser desorption/ionization-time of flight mass spectrometry is a useful analytical tool to study the hydrolysis of these hormones by dipeptidyl peptidase IV, including kinetic analysis. Spectra indicated that serumincubated peptides were cleaved by this enzyme with only minor secondary degradation due to other serum protease activity. Quantification of the mass spectrometric signals allowed kinetic constants for both porcine kidney-and human serum dipeptidyl peptidase IVcatalyzed incretin hydrolysis to be calculated. The binding constants (K m ) of these incretins to purified porcine kidney-derived enzyme were 1.8 ؎ 0.3 and 3.8 ؎ 0.3 M, whereas the binding constants observed in human serum were 39 ؎ 29 and 13 ؎ 9 M for glucose-dependent-insulinotropic polypeptide and glucagon-like peptide-1-(7-36)-amide respectively. The large range of K m values found in human serum suggests a heterogeneous pool of enzyme. The close correlation between the reported kinetic constants and those previously described validates this novel approach to kinetic analysis.Incretins are hormones of the enteroinsular axis, which potentiate the actions of glucose on the endocrine pancreas (1). The most potent known incretins are glucose-dependent insulinotropic polypeptide (GIP 1 and truncated forms of glucagon-like peptide-1 (GLP-1 7-36 -amide and GLP-1 7-37 ); both are members of the glucagon family of hormones sharing considerable N-terminal sequence homology (2, 3). Both hormones are released from the gut in response to ingested nutrients and were recently shown to be substrates of the circulating exopeptidase dipeptidyl peptidase IV (DP IV, EC 3.4.14.5) (4, 5). This enzyme is a highly specific protease, preferentially hydrolyzing peptides with N-terminal Xaa-Pro and Xaa-Ala motifs (6). Hydrolysis of GIP 1-42 and GLP-1 7-36 by DP IV yields GIP 3-42 and GLP-1 9 -36 and the dipeptides Tyr-Ala and His-Ala, respectively. Activation or inactivation of biologically active peptides is frequently associated with DP IV catalysis. Work by ourselves and others (7,8) has demonstrated that GIP 3-42 and GLP-1 9 -36 are biologically inactive, and it has been hypothesized that serum degradation of GIP 1-42 and GLP-1 7-36 by DP IV is the primary step in the metabolism of these hormones in the circulation (4, 5, 9). In 1993 Mentlein and co-workers (4) reported on the kinetics of enzymatic degradation of GIP 1-42 and GLP-1 7-36 by purified human placental DP IV, as determined by high performance liquid chromatography (HPLC), and suggested that this may be a physiologically important pathway for the degradation of these hormones. This ...

No abstract

Alzheimer’s disease (AD) and Parkinson’s disease (PD), including dementia with Lewy bodies (DLB), account for the majority of dementia cases worldwide. Interestingly, a significant number of patients have clinical and neuropathological features of both AD and PD, i.e., the presence of amyloid deposits and Lewy bodies in the neocortex. The identification of α-synuclein peptides in amyloid plaques in DLB brain led to the hypothesis that both peptides mutually interact with each other to facilitate neurodegeneration. In this article, we report the influence of Aβ(1–42) and pGlu-Aβ(3–42) on the aggregation of α-synuclein in vitro. The aggregation of human recombinant α-synuclein was investigated using thioflavin-T fluorescence assay. Fibrils were investigated by means of antibody conjugated immunogold followed by transmission electron microscopy (TEM). Our data demonstrate a significantly increased aggregation propensity of α-synuclein in the presence of minor concentrations of Aβ(1–42) and pGlu-Aβ(3–42) for the first time, but without effect on toxicity on mouse primary neurons. The analysis of the composition of the fibrils by TEM combined with immunogold labeling of the peptides revealed an interaction of α-synuclein and Aβ in vitro, leading to an accelerated fibril formation. The analysis of kinetic data suggests that significantly enhanced nucleus formation accounts for this effect. Additionally, co-occurrence of α-synuclein and Aβ and pGlu-Aβ, respectively, under pathological conditions was confirmed in vivo by double immunofluorescent labelings in brains of aged transgenic mice with amyloid pathology. These observations imply a cross-talk of the amyloid peptides α-synuclein and Aβ species in neurodegeneration. Such effects might be responsible for the co-occurrence of Lewy bodies and plaques in many dementia cases.

Murine glutaminyl cyclase (mQC) was identified in the insulinoma cell line beta-TC 3 by determination of enzymatic activity and RT-PCR. The cloned cDNA was expressed in the secretory pathway of the methylotrophic yeast Pichia pastoris and purified after fermentation using a new three-step protocol. mQC converted a set of various substrates with very similar specificity to human QC, indicating a virtually identical catalytic competence. Furthermore, mQC was competitively inhibited by imidazole derivatives. A screen of thiol reagents revealed cysteamine as a competitive inhibitor of mQC bearing a Ki value of 42 +/-2 microM. Substitution of the thiol or the amino group resulted in a drastic loss of inhibitory potency. The pH dependence of catalysis and inhibition support that an uncharged nitrogen of the inhibitors and the substrate is necessary in order to bind to the active site of the enzyme. In contrast to imidazole and cysteamine, the heterocyclic chelators 1,10-phenanthroline, 2,6-dipicolinic acid, and 8-hydroxyquinoline inactivated mQC in a time-dependent manner. In addition, citric acid inactivated the enzyme at pH 5.5. Inhibition by citrate was abolished in the presence of zinc ions. A determination of the metal content by total reflection X-ray fluorescence spectrometry and atomic absorption spectroscopy in mQC revealed stoichiometric amounts of zinc bound to the protein. Metal ion depletion appeared to have no significant effect on protein structure as shown by fluorescence spectroscopy, suggesting a catalytic role of zinc. The results demonstrate that mQC and probably all animal QCs are zinc-dependent catalysts. Apparently, during evolution from an ancestral protease, a switch occurred in the catalytic mechanism which is mainly based on a loss of one metal binding site.

Modified amyloid β (Aβ) peptides represent major constituents of the amyloid deposits in Alzheimer’s disease and Down’s syndrome. In particular, N‐terminal pyroglutamate (pGlu) following truncation renders Aβ more stable, increases hydrophobicity and the aggregation velocity. Recent evidence based on in vitro studies suggests that the cyclization of glutamic acid, leading to pGlu‐Aβ, is catalyzed by the enzyme glutaminyl cyclase (QC) following limited proteolysis of Aβ at the N‐terminus. Here, we studied the pGlu‐formation by rat QC in vitro as well as after microinjection of Aβ(1–40) and Aβ(3–40) into the rat cortex in vivo/in situ with and without pharmacological QC inhibition. Significant pGlu‐Aβ formation was observed following injection of Aβ(3–40) after 24 h, indicating a catalyzed process. The generation of pGlu‐Aβ from Aβ(3–40) was significantly inhibited by intracortical microinjection of a QC inhibitor. The study provides first evidence that generation of pGlu‐Aβ is a QC‐catalyzed process in vivo. The approach per se offers a strategy for a rapid evaluation of compounds targeting a reduction of pGlu formation at the N‐terminus of amyloid peptides.

No abstract