Glenn E. Dale

X-ray structure of junctional adhesion molecule: structural basis for homophilic adhesion via a novel dimerization motif

Junctional adhesion molecules (JAMs) are a family of immunoglobulin‐like single‐span transmembrane molecules that are expressed in endothelial cells, epithelial cells, leukocytes and myocardia. JAM has been suggested to contribute to the adhesive function of tight junctions and to regulate leukocyte trans migration. We describe the crystal structure of the recombinant extracellular part of mouse JAM (rsJAM) at 2.5 Å resolution. rsJAM consists of two immunoglobulin‐like domains that are connected by a conformationally restrained short linker. Two rsJAM molecules form a U‐shaped dimer with highly complementary interactions between the N‐terminal domains. Two salt bridges are formed in a complementary manner by a novel dimerization motif, R(V,I,L)E, which is essential for the formation of rsJAM dimers in solution and common to the known members of the JAM family. Based on the crystal packing and studies with mutant rsJAM, we propose a model for homophilic adhesion of JAM. In this model, U‐shaped JAM dimers are oriented in cis on the cell surface and form a two‐dimensional network by trans‐interactions of their N‐terminal domains with JAM dimers from an opposite cell surface.

The protein as a variable in protein crystallization.

Strategies for growing protein crystals have for many years been essentially empirical, the protein, once purified to a certain homogeneity, being mixed with a selection of crystallization agents selected in a more or less trial-and-error fashion. Screening for the correct conditions has been made easier through automation and by the introduction of commercially available crystallization kits. Many parameters can be changed in these experiments, such as temperature, pH, and ionic strength, but perhaps the most important variable has been ignored, namely the protein. The crystallization properties of a protein vary greatly: some crystallize readily, whereas others have proven extremely difficult or even impossible to obtain in a crystalline state. The possibility of altering the intrinsic characteristics of a protein for crystallization has become a feasible strategy. Some historical perspectives and advances in this area will be reviewed.

High-resolution structure of human apo dipeptidyl peptidase IV/CD26 and its complex with 1-[([2-[(5-iodopyridin-2-yl)amino]-ethyl]amino)-acetyl]-2-cyano-(S)-pyrrolidine.

Dipeptidyl peptidase IV is a multifunctional type II transmembrane serine protease glycoprotein. The high-resolution crystal structure of the homodimeric human apo dipeptidyl peptidase IV has been determined at 1.9 A resolution. In addition, the structure of the binary complex with 1-[([2-[(5-iodopyridin-2-yl)amino]-ethyl]amino)-acetyl]-2-cyano-(S)-pyrrolidine has been solved, revealing the nature of the covalent interaction with the active-site serine.

Mapping the active site of Escherichia coli malonyl-CoA-acyl carrier protein transacylase (FabD) by protein crystallography.

Malonyl-CoA-acyl carrier protein transacylase (FabD; EC 2.3.1.39) is a key enzyme in the fatty-acid biosynthesis pathway of bacteria, catalyzing the transfer of a malonyl moiety from malonyl-CoA to holo acyl carrier protein (ACP), generating malonyl-ACP and free CoASH. Malonyl-ACP, which is the product of this reaction, is the key building block for de novo fatty-acid biosynthesis. Various binary complex structures of the Escherichia coli enzyme are presented, including that of the natural substrate malonyl-CoA, indicating the functional role of the highly conserved amino acids Gln11, Ser92, Arg117 and His201 and the stabilizing function of the preformed oxyanion hole during the enzymatic reaction. Based on the presented structural data, a possible new catalytic enzyme mechanism is discussed. The data obtained could be used in aiding the process of rational inhibitor design.

Structural analysis of neprilysin with various specific and potent inhibitors.

Neutral endopeptidase (NEP) is the major enzyme involved in the metabolic inactivation of a number of bioactive peptides including the enkephalins, substance P, endothelin, bradykinin and atrial natriuretic factor. Owing to the physiological importance of NEP in the modulation of nociceptive and pressor responses, there is considerable interest in inhibitors of this enzyme as novel analgesics and antihypertensive agents. Here, the crystal structures of the soluble extracellular domain of human NEP (residues 52-749) complexed with various potent and competitive inhibitors are described. The structures unambiguously reveal the binding mode of the different zinc-chelating groups and the subsite specificity of the enzyme.

Increased hydrophobic interactions of iclaprim with Staphylococcus aureus dihydrofolate reductase are responsible for the increase in affinity and antibacterial activity

OBJECTIVES Iclaprim is a novel 2,4-diaminopyrimidine that exhibits potent, rapid bactericidal activity against major Gram-positive pathogens, including methicillin-susceptible Staphylococcus aureus and methicillin-resistant S. aureus, and is currently in clinical development for the treatment of complicated skin and skin structure infections. An understanding of the known mechanism of resistance to trimethoprim led to the design of this new inhibitor, with improved affinity towards dihydrofolate reductase (DHFR) from S. aureus and clinically useful activity against S. aureus including isolates resistant to trimethoprim. The objective of this study was to characterize the mode of action of iclaprim and its inhibitory properties against DHFR. METHODS The mode of action of iclaprim was assessed by enzymatic analysis, direct binding studies, macromolecular synthesis profiles, synergy and antagonism studies to define its role as an inhibitor of DHFR. The binding properties of iclaprim to DHFR were compared with those of trimethoprim by X-ray crystallography. RESULTS The enzymatic properties, direct binding and X-ray crystallographic studies delineated the mode of interaction with DHFR and the reason for the increased affinity of iclaprim towards the enzyme. The effect of iclaprim on bacterial physiology suggests that iclaprim behaves as a classical antibacterial DHFR inhibitor, as previously documented for trimethoprim. CONCLUSIONS Iclaprim binds and inhibits bacterial DHFR in a similar manner to trimethoprim. However, the increased hydrophobic interactions between iclaprim and DHFR account for increased affinity and, unlike trimethoprim, enable iclaprim to inhibit even the resistant enzyme with nanomolar affinity, thus overcoming the mechanism of trimethoprim resistance. The increased antibacterial activity and lower propensity for resistance make iclaprim a clinically promising and useful inhibitor.

Cloning and characterization of a novel, plasmid-encoded trimethoprim-resistant dihydrofolate reductase from Staphylococcus haemolyticus MUR313.

In recent years resistance to the antibacterial agent trimethoprim (Tmp) has become more widespread, and several trimethoprim-resistant (Tmpr) dihydrofolate reductases (DHFRs) have been described from gram-negative bacteria. In staphylococci, only one Tmpr DHFR has been described, the type S1 DHFR, which is encoded by the dfrA gene found on transposon Tn4003. In order to investigate the coincidence of high-level Tmp resistance and the presence of dfrA, we analyzed the DNAs from various Tmpr staphylococci for the presence of dfrA sequences by PCR with primers specific for the thyE-dfrA genes from Tn4003. We found that 30 or 33 isolates highly resistant to Tmp (MICs, > or = 512 micrograms/ml) contained dfrA sequences, whereas among the Tmpr (MICs, < or = 256 micrograms/ml) and Tmps isolates only the Staphylococcus epidermidis isolates (both Tmpr and Tmps) seemed to contain the dfrA gene. Furthermore, we have cloned and characterized a novel, plasmid-encoded Tmpr DHFR from Staphylococcus haemolyticus MUR313. The dfrD gene of plasmid pABU17 is preceded by two putative Shine-Dalgarno sequences potentially allowing for the start of translation at two triplets separated by nine nucleotides. The predicted protein of 166 amino acids, designated S2DHFR, encoded by the longer open reading frame was overproduced in Escherichia coli, purified, and characterized. The molecular size of the recombinant S2DHFR was determined by ion spray mass spectrometry to be 19,821.2 +/- 2 Da, which is in agreement with the theoretical value of 19,822 Da. In addition, the recombinant S2DHFR was shown to exhibit DHFR activity and to be highly resistant to Tmp.

A continuous coupled enzyme assay for bacterial malonyl–CoA:acyl carrier protein transacylase (FabD)

Bacterial malonyl-CoA:acyl carrier protein transacylase catalyzes the transfer of a malonyl moiety from malonyl-CoA to the free thiol group of the phosphopantetheine arm of acyl carrier protein. Malonyl-ACP, the product of this enzymatic reaction, is the key building block for de novo fatty acid biosynthesis. Here, we describe a continuous enzyme assay based on the coupling of the malonyl-CoA:acyl carrier protein transacylase reaction to alpha-ketoglutarate dehydrogenase (KDH). KDH-dependent consumption of the coenzyme A generated by malonyl-CoA:acyl carrier protein transacylase is accompanied by a reduction of nicotinamide adenine dinucleotide, oxidized (NAD(+)) to nicotinamide adenine dinucleotide, reduced. The rate of NAD(+) reduction is continuously monitored as a change in fluorescence using a microtiter plate reader. We show that this coupled enzyme assay is amenable to routine chemical compound screening.

Structure of human endothelin-converting enzyme I complexed with phosphoramidon

Endothelin-converting enzyme I (ECE-1) is a mammalian type II integral membrane zinc-containing endopeptidase. ECE-1 catalyzes the final step in the biosynthesis of endothelins in a rate-limiting fashion, through post-translational conversion of the biologically inactive big endothelins. Endothelin-1 overproduction has been implicated in a heterogeneous list of diseases including systemic and pulmonary hypertension, stroke and asthma, cardiac and renal failure. Therefore, ECE-1 is a prime therapeutic target for the regulation of endothelin-1 production in vivo and there is considerable interest in selective inhibitors of this enzyme. Here, we present the crystal structure of the extracellular domain (residues 90-770) of human ECE-1 (C428S) with the generic metalloprotease inhibitor phosphoramidon determined at 2.38 A resolution. The structure is closely related to that of human NEP, providing essential information for a detailed understanding of ligand-binding, specificity determinants as well as selectivity criteria. Selective inhibitors of ECE-1s should have beneficial effects for the treatment of diseases in which an overproduction of ETs plays a pathogenic role.

Structural studies of a bifunctional inhibitor of neprilysin and DPP-IV.

Neutral endopeptidase (NEP) is the major enzyme involved in the metabolic inactivation of a number of bioactive peptides including the enkephalins, substance P, endothelin, bradykinin and atrial natriuretic factor, as well as the incretin hormone glucagon-like peptide 1 (GLP-1), which is a potent stimulator of insulin secretion. The activity of GLP-1 is also rapidly abolished by the serine protease dipeptidyl peptidase IV (DPP-IV), which led to an elevated interest in inhibitors of this enzyme for the treatment of type II diabetes. A dual NEP/DPP-IV inhibitor concept is proposed, offering an alternative strategy for the treatment of type 2 diabetes. Here, the synthesis and crystal structures of the soluble extracellular domain of human NEP (residues 52-749) complexed with the NEP, competitive and potent dual NEP/DPP-IV inhibitor MCB3937 are described.