N-terminal pyroglutamate (pGlu) formation from its glutaminyl (or glutamyl) precursor is required in the maturation of numerous bioactive peptides. The aberrant formation of pGlu may be related to several pathological processes, such as osteoporosis and amyloidotic diseases. This N-terminal cyclization reaction, once thought to proceed spontaneously, is greatly facilitated by the enzyme glutaminyl cyclase (QC). To probe this important but poorly understood modification, we present here the structure of human QC in free form and bound to a substrate and three imidazole-derived inhibitors. The structure reveals an ␣͞␤ scaffold akin to that of two-zinc exopeptidases but with several insertions and deletions, particularly in the active-site region. The relatively closed active site displays alternate conformations due to the different indole orientations of Trp-207, resulting in two substrate (glutamine t-butyl ester)-binding modes. The single zinc ion in the active site is coordinated to three conserved residues and one water molecule, which is replaced by an imidazole nitrogen upon binding of the inhibitors. Together with structural and kinetic analyses of several active-site-mutant enzymes, a catalysis mechanism of the formation of protein N-terminal pGlu is proposed. Our results provide a structural basis for the rational design of inhibitors against QC-associated disorders.crystallography ͉ intramolecular cyclization ͉ posttranslational modification ͉ Alzheimer's disease ͉ aminopeptidase N -terminal pyroglutamate (pGlu) formation from its glutaminyl precursor is an important posttranslational or cotranslational event in the processing of numerous bioactive neuropeptides, hormones, and cytokines during their maturation in the secretory pathway. These regulatory peptides require the N-terminal pGlu to develop the proper conformation for binding to their receptors and͞or to protect the N termini of the peptides from exopeptidase degradation (1, 2). Previously, this Nterminal cyclization reaction was thought to proceed spontaneously, until the glutaminyl cyclases (QCs) were identified as catalysts that are responsible for this posttranslational modification (3, 4).QCs (EC 2.3.2.5) are acyltransferases that have been identified in both animal and plant sources (3-5). They are abundant in mammalian neuroendocrine tissues, such as hypothalamus and pituitary (4, 6), and are highly conserved from yeast to human. Animal QCs were shown to have distinct structure and protein stability from plant QCs despite their similar molecular masses [i.e., 33-40 kDa (5, 7)]. No bacterial QCs have been reported thus far; however, the mammalian QCs were predicted to exhibit remarkable homology to the bacterial double-zinc aminopeptidases (8, 9).In humans, several genetic diseases, such as osteoporosis, a multifactorial hormonal disease that is characterized by reduced bone mass and microarchitectural deterioration of bone tissue (10), appear to result from mutations of the QC gene. The gene encoding QC (QPCT) lies on chromosome 2p22.3. ...

Middle East respiratory syndrome coronavirus (MERS-CoV) causes severe acute respiratory illness with fever, cough and shortness of breath. Up to date, it has resulted in 1826 human infections, including 649 deaths. Analogous to picornavirus 3C protease (3C), 3C-like protease (3CL) is critical for initiation of the MERS-CoV replication cycle and is thus regarded as a validated drug target. As presented here, our peptidomimetic inhibitors of enterovirus 3C (6b, 6c and 6d) inhibited 3CL of MERS-CoV and severe acute respiratory syndrome coronavirus (SARS-CoV) with IC values ranging from 1.7 to 4.7 μM and from 0.2 to 0.7 μM, respectively. In MERS-CoV-infected cells, the inhibitors showed antiviral activity with EC values ranging from 0.6 to 1.4 μM, by downregulating the viral protein production in cells as well as reducing secretion of infectious viral particles into culture supernatants. They also suppressed other α- and β-CoVs from human and feline origin. These compounds exhibited good selectivity index (over 70 against MERS-CoV) and could lead to the development of broad-spectrum antiviral drugs against emerging CoVs and picornaviruses.

With an increase in antibiotic-resistant strains, the nosocomial pathogen Acinetobacter baumannii has become a serious threat to global health. Glycoconjugate vaccines containing fragments of bacterial exopolysaccharide (EPS) are an emerging therapeutic to combat bacterial infection. Herein, we characterize the bacteriophage ΦAB6 tailspike protein (TSP), which specifically hydrolyzed the EPS of A. baumannii strain 54149 (Ab-54149). Ab-54149 EPS exhibited the same chemical structure as two antibiotic-resistant A. baumannii strains. The ΦAB6 TSP-digested products comprised oligosaccharides of two repeat units, typically with stoichiometric pseudaminic acid (Pse). The 1.48-1.89-Å resolution crystal structures of an N-terminally-truncated ΦAB6 TSP and its complexes with the semi-hydrolyzed products revealed a trimeric β-helix architecture that bears intersubunit carbohydrate-binding grooves, with some features unusual to the TSP family. The structures suggest that Pse in the substrate is an important recognition site for ΦAB6 TSP. A region in the carbohydrate-binding groove is identified as the determinant of product specificity. The structures also elucidated a retaining mechanism, for which the catalytic residues were verified by site-directed mutagenesis. Our findings provide a structural basis for engineering the enzyme to produce desired oligosaccharides, which is useful for the development of glycoconjugate vaccines against A. baumannii infection.

In this study, we report the structure and function of a lectin from the sea mollusk Crenomytilus grayanus collected from the sublittoral zone of Peter the Great Bay of the Sea of Japan. The crystal structure of C. grayanus lectin (CGL) was solved to a resolution of 1.08 Å, revealing a β-trefoil fold that dimerizes into a dumbbell-shaped quaternary structure. Analysis of the crystal CGL structures bound to galactose, galactosamine, and globotriose Gb3 indicated that each CGL can bind three ligands through a carbohydrate-binding motif involving an extensive histidine- and water-mediated hydrogen bond network. CGL binding to Gb3 is further enhanced by additional side-chain-mediated hydrogen bonds in each of the three ligand-binding sites. NMR titrations revealed that the three binding sites have distinct microscopic affinities toward galactose and galactosamine. Cell viability assays showed that CGL recognizes Gb3 on the surface of breast cancer cells, leading to cell death. Our findings suggest the use of this lectin in cancer diagnosis and treatment.