Biomedical subjects

Patrick J Loll

Publications and source records attributed to Patrick J Loll.

11 recordsLinked to original sources

PubMed2006

Photoactive analogues of the haloether anesthetics provide high-resolution features from low-affinity interactions.

The difficulty in obtaining binding target and site information for low-affinity drugs, like the inhaled anesthetics, has limited identification of their molecular effectors. Because such information can be provided by photoactive analogues, we designed, synthesized, and characterized a novel diazirnyl haloether that closely mimics isoflurane, the most widely used clinical general anesthetic. This compound, H-diaziflurane, is a nontoxic, potent anesthetic that potentiates GABA-gated ion channels in primary cultures of hippocampal neurons. Calorimetric and structural characterizations show that H-diaziflurane binds a model anesthetic host protein with similar energetics as isoflurane and forms photoadducts with residues lining the isoflurane binding site. H-diaziflurane will be immediately useful for identifying targets and sites important for the molecular pharmacology of the inhaled haloether anesthetics.

Anesthetics↗

PubMed2006

2.0 angstroms structure of prostaglandin H2 synthase-1 reconstituted with a manganese porphyrin cofactor.

Prostaglandin H2 synthase (EC 1.14.99.1) is a clinically important drug target that catalyzes two key steps in the biosynthesis of the eicosanoid hormones. The enzyme contains spatially distinct cyclooxygenase and peroxidase active sites, both of which require a heme cofactor. Substitution of ferric heme by Mn(III) protoporphyrin IX greatly diminishes the peroxidase activity, but has little effect on the cyclooxygenase activity. Here, the 2.0 angstroms resolution crystal structure of the Mn(III) form of ovine prostaglandin H2 synthase-1 is described (R = 21.8%, R(free) = 23.7%). Substitution of Mn(III) for Fe(III) causes no structural perturbations in the protein. However, the out-of-plane displacement of the manganese ion with respect to the porphyrin is greater than that of the iron by approximately 0.2 angstroms. This perturbation may help to explain the altered catalytic properties of the manganese enzyme.

Animals↗

PubMed2005

Structural basis for high-affinity volatile anesthetic binding in a natural 4-helix bundle protein.

Physiologic sites for inhaled anesthetics are presumed to be cavities within transmembrane 4-alpha-helix bundles of neurotransmitter receptors, but confirmation of binding and structural detail of such sites remains elusive. To provide such detail, we screened soluble proteins containing this structural motif, and found only one that exhibited evidence of strong anesthetic binding. Ferritin is a 24-mer of 4-alpha-helix bundles; both halothane and isoflurane bind with K(A) values of approximately 10(5) M(-1), higher than any previously reported inhaled anesthetic-protein interaction. The crystal structures of the halothane/apoferritin and isoflurane/apoferritin complexes were determined at 1.75 A resolution, revealing a common anesthetic binding pocket within an interhelical dimerization interface. The high affinity is explained by several weak polar contacts and an optimal host/guest packing relationship. Neither the acidic protons nor ether oxygen of the anesthetics contribute to the binding interaction. Compared with unliganded apoferritin, the anesthetic produced no detectable alteration of structure or B factors. The remarkably high affinity of the anesthetic/apoferritin complex implies greater selectivity of protein sites than previously thought, and suggests that direct protein actions may underlie effects at lower than surgical levels of anesthetic, including loss of awareness.

Anesthetics, Inhalation↗

PubMed2004

Colicin occlusion of OmpF and TolC channels: outer membrane translocons for colicin import.

The interaction of colicins with target cells is a paradigm for protein import. To enter cells, bactericidal colicins parasitize Escherichia coli outer membrane receptors whose physiological purpose is the import of essential metabolites. Colicins E1 and E3 initially bind to the BtuB receptor, whose beta-barrel pore is occluded by an N-terminal globular "plug". The x-ray structure of a complex of BtuB with the coiled-coil BtuB-binding domain of colicin E3 did not reveal displacement of the BtuB plug that would allow passage of the colicin (Kurisu, G., S. D. Zakharov, M. V. Zhalnina, S. Bano, V. Y. Eroukova, T. I. Rokitskaya, Y. N. Antonenko, M. C. Wiener, and W. A. Cramer. 2003. Nat. Struct. Biol. 10:948-954). This correlates with the inability of BtuB to form ion channels in planar bilayers, shown in this work, suggesting that an additional outer membrane protein(s) is required for colicin import across the outer membrane. The identity and interaction properties of this OMP were analyzed in planar bilayer experiments.OmpF and TolC channels in planar bilayers were occluded by colicins E3 and E1, respectively, from the trans-side of the membrane. Occlusion was dependent upon a cis-negative transmembrane potential. A positive potential reversibly opened OmpF and TolC channels. Colicin N, which uses only OmpF for entry, occludes OmpF in planar bilayers with the same orientation constraints as colicins E1 and E3. The OmpF recognition sites of colicins E3 and N, and the TolC recognition site of colicin E1, were found to reside in the N-terminal translocation domains. These data are considered in the context of a two-receptor translocon model for colicin entry into cells.

Bacterial Outer Membrane Proteins↗

PubMed2004

Manipulation of kinetic profiles in 2-aryl propionic acid cyclooxygenase inhibitors.

The nonsteroidal anti-inflammatory drugs flurbiprofen and ibuprofen were modified in an attempt to alter the kinetics of inhibitor binding by COX-1. Contrary to prior predictions, a halogen substituent is not sufficient to confer slow tight-binding behavior. Conversion of the carboxylate moiety of flurbiprofen to an ester or amide abolishes slow tight-binding behavior, regardless of halogenation state.

Animals↗

PubMed2004

The 2.0 A resolution crystal structure of prostaglandin H2 synthase-1: structural insights into an unusual peroxidase.

Prostaglandin H2 synthase (EC 1.14.99.1) is an integral membrane enzyme containing a cyclooxygenase site, which is the target for the non-steroidal anti-inflammatory drugs, and a spatially distinct peroxidase site. Previous crystallographic studies of this clinically important drug target have been hindered by low resolution. We present here the 2.0 A resolution X-ray crystal structure of ovine prostaglandin H2 synthase-1 in complex with alpha-methyl-4-biphenylacetic acid, a defluorinated analog of the non-steroidal anti-inflammatory drug flurbiprofen. Detergent molecules are seen to bind to the protein's membrane-binding domain, and their positions suggest the depth to which this domain is likely to penetrate into the lipid bilayer. The relation of the enzyme's proximal heme ligand His388 to the heme iron is atypical for a peroxidase; the iron-histidine bond is unusually long and a substantial tilt angle is observed between the heme and imidazole planes. A molecule of glycerol, used as a cryoprotectant during diffraction experiments, is seen to bind in the peroxidase site, offering the first view of any ligand in this active site. Insights gained from glycerol binding may prove useful in the design of a peroxidase-specific ligand.

Animals↗

PubMed2003

Compatibility of detergents with the microbatch-under-oil crystallization method.

Detergents are required to solubilize integral membrane proteins and are common components of the solutions used to crystallize these molecules. It has been unclear whether these detergents are completely compatible with the oils used in the microbatch-under-oil crystallization technique, because they might conceivably be lost from solution by partitioning into the oil phase. The partitioning of the detergents n-octyl-beta-d-glucopyranoside and Fos-Choline-12 into two different oils used for microbatch crystallization experiments has been examined. It was found that vigorous mixing and prolonged incubation of the aqueous detergent solutions with the oils leads to small losses of detergent (approximately 5% of the total detergent mass); however, gentle mixing that is more typical of the mixing encountered in a crystallization experiments leads to negligible loss of detergent.

Crystallization↗

PubMed2003

Configurational entropy and cooperativity between ligand binding and dimerization in glycopeptide antibiotics.

Oligomerization and ligand binding are thermodynamically cooperative processes in many biochemical systems, and the mechanisms giving rise to cooperative behavior are generally attributed to changes in structure. In glycopeptide antibiotics, however, these cooperative processes are not accompanied by significant structural changes. To investigate the mechanism by which cooperativity arises in these compounds, fully solvated molecular dynamics simulations and quasiharmonic normal-mode analysis were performed on chloroeremomycin, vancomycin, and dechlorovancomycin. Configurational entropies were derived from the vibrational modes recovered from ligand-free and ligand-bound forms of the monomeric and dimeric species. Results indicate that both ligand binding and dimerization incur an entropic cost as vibrational activity in the central core of the antibiotic is shifted to higher frequencies with lower amplitudes. Nevertheless, ligand binding and dimerization are cooperative because the entropic cost of both processes occurring together is less than the cost of these processes occurring separately. These reductions in configurational entropy are more than sufficient in magnitude to account for the experimentally observed cooperativity between dimerization and ligand binding. We conclude that biochemical cooperativity can be mediated through changes in vibrational activity, irrespective of the presence or absence of concomitant structural change. This may represent a general mechanism of allostery underlying cooperative phenomena in diverse macromolecular systems.

Anti-Bacterial Agents↗

PubMed2003

Membrane protein structural biology: the high throughput challenge.

Membrane proteins represent roughly one-third of the proteins encoded in the genome, yet fewer than 1% of the proteins are of known structure. High-throughput crystallography offers the hope of correcting this imbalance. In order for large-scale membrane protein structural biology to realize its full promise, however, significant technical challenges must be overcome, the two most substantial being facile protein overexpression and reliable methods for crystal growth.

Cloning, Molecular↗

PubMed2002

The role of configurational entropy in biochemical cooperativity.

Cooperativity is a common biochemical phenomenon in which two or more otherwise independent processes are thermodynamically coupled. Because cooperative processes are usually attended by changes in molecular conformation, thermodynamic coupling is usually attributed to an enthalpy-driven mechanism. In the family of glycopeptide antibiotics that includes vancomycin, however, cooperative phenomena occur that cannot be explained by conformational change. In this communication, we demonstrate that cooperativity in these systems can arise solely from changes in vibrational activity.

Alanine↗

PubMedDate not supplied

Real-time monitoring of the membrane-binding and insertion properties of the cholesterol-dependent cytolysin anthrolysin O from Bacillus anthracis.

Bacillus anthracis has recently been shown to secrete a potently hemolytic/cytolytic protein that has been designated anthrolysin O (ALO). In this work, we initiated a study of this potential anthrax virulence factor in an effort to understand the membrane-binding properties of this protein. Recombinant anthrolysin O (rALO35-512) and two N-terminally truncated versions of ALO (rALO390-512 and rALO403-512) from B. anthracis were overproduced in Escherichia coli and purified to homogeneity. The role of cholesterol in the cytolytic activity of ALO was probed in cellular cholesterol depletion assays using mouse and human macrophage-like lines, and also Drosophila Schneider 2 cells. Challenging the macrophage cells with rALO35-512, but not rALO390-512 or rALO403-512, resulted in cell death by lysis, with this cytolysis being abolished by depletion of the membrane cholesterol. Drosophila cells, which contain ergosterol as their major membrane sterol, were resistant to rALO-mediated cytolysis. In order to determine the molecular mechanism of this resistance, the interaction of rALO with model membranes comprised of POPC alone, or with a variety of structurally similar sterols including ergosterol, was probed using Biacore. Both rALO35-512 and rALO403-512 demonstrated robust binding to model membranes composed of POPC and cholesterol, with amount of protein bound proportional to the cholesterol content. Ergosterol supported greatly reduced binding of both rALO35-512 and rALO403-512, whereas other sterols tested did not support binding. The rALO403-512--membrane interaction demonstrated an equilibrium dissociation constant (KD) in the low nanomolar range, whereas rALO35-512 exhibited complex kinetics likely due to the multiple events involved in pore formation. These results establish the pivotal role of cholesterol in the action of rALO. The biosensor method developed to measure ALO recognition of cholesterol in a membrane environment could be extended to provide a platform for the screening of inhibitors of other membrane-binding proteins and peptides.

Animals↗