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L B Cole

Publications and source records attributed to L B Cole.

12 recordsLinked to original sources
PubMed1998

Structure of 3,4-dichloroisocoumarin-inhibited factor D.

Factor D (D) is a serine protease essential in the activation of the alternative complement pathway. Only a few of the common serine protease inhibitors inhibit D, binding covalently to the serine hydroxyl of the catalytic triad. 3,4-Dichloroisocoumarin (DCI) is a mechanism-based inhibitor which inhibits most serine proteases and many esterases, including D. The structure of the enzyme:inhibitor covalent adduct of D with DCI, DCI:D, to a resolution of 1.8 A is described, which represents the first structural analysis of D with a mechanism-based inhibitor. The side chain of the ring-opened DCI moiety of the protein adduct undergoes chemical modification in the buffered solution, resulting in the formation of an alpha-hydroxy acid moiety through the nucleophilic substitution of both Cl atoms. The inhibited enzyme is similar in overall structure to the native enzyme, as well as to a variety of isocoumarin-inhibited trypsin and porcine pancreatic elastase (PPE) structures, yet notable differences are observed in the active site and binding mode of these small-molecule inhibitors. One region of the active site (residues 189-195) is relatively conserved between factor D, trypsin, and elastase with respect to amino-acid sequence and to conformation. Another region (residues 214-220) reflects the amino-acid substitutions and conformational flexibility between these enzymes. The carbonyl O atom of the DCI moiety was found to be oriented away from the oxyanion hole, which greatly contributes to the stability of the DCI:D adduct. The comparisons of the active sites between native factor D, DCI-inhibited factor D, and various inhibited trypsin and elastase (PPE) molecules are providing the chemical bases directing our design of novel, small-molecule pharmaceutical agents capable of modulating the alternative complement pathway.

Animals↗
PubMed1997

Design and synthesis of benzoic acid derivatives as influenza neuraminidase inhibitors using structure-based drug design.

A series of 94 benzoic acid derivatives was synthesized and tested for its ability to inhibit influenza neuraminidase. The enzyme-inhibitor complex structure was determined by X-ray crystallographic analysis for compounds which inhibited the enzyme. The most potent compound tested in vitro, 5 (4-acetylamino)-3-guanidinobenzoic acid), had an IC50 = 2.5 x 10(-6) M against N9 neuraminidase. Compound 5 was oriented in the active site of the neuraminidase in a manner that was not predicted from the reported active site binding of GANA (4) with neuraminidase. In a mouse model of influenza, 5 did not protect the mice from weight loss due to the influenza virus when dosed intranasally.

Animals↗
PubMed1997

Structure of diisopropyl fluorophosphate-inhibited factor D.

Factor D (D) is a serine protease, crucial for the activation of the alternative complement pathway. Only a limited number of general serine protease inhibitors are known to inhibit D, most of which covalently bind to the serine hydroxyl of the catalytic triad. The structure of the first enzyme:inhibitor covalent adduct of D with diisopropyl fluorophosphate (DIP:D) to a resolution of 2.4 A is described. The inhibited enzyme is similar in overall structure to the native enzyme and to trypsin, yet exhibits notable differences in the active site. One region of the active site is conserved between D and trypsin with respect to amino-acid sequence and to conformation. Another reflects the amino-acid substitutions and conformational flexibility between these enzymes. The active-site histidine residue is observed in the gauche+ conformation, not the normal gauche- orientation seen in the classic catalytic triad arrangement required for enzymatic activity in serine proteases. Comparisons of the active sites between native D, the DIP:D adduct, and DIP-inhibited trypsin have provided fundamental insights currently being employed in the design of novel small-molecule pharmaceutical agents capable of modulating the alternative complement pathway.

Journal Article↗
PubMed1994

Probing protein-protein interactions. The ribose-binding protein in bacterial transport and chemotaxis.

A number of mutations at Gly134 of the periplasmic ribose-binding protein of Escherichia coli were examined by a combined biochemical and structural approach. Different mutations gave rise to different patterns of effects on the chemotaxis and transport functions. The smallest residue (alanine) had the least effect on transport, whereas large hydrophobic residues had the smallest effect on chemotaxis. Comparison of the x-ray crystal structure of the G134R mutant protein (2.5-A resolution) to that of the wild type (1.6-A resolution) showed that the basic structure of the protein was unaltered. The loss of chemotaxis and transport functions in this and similar mutant proteins must therefore be caused by relatively simple surface effects, which include a change in local main chain conformation. The loss of chemotaxis and transport functions resulting from the introduction of an alanine residue at position 134 was suppressed by an additional isoleucine to threonine mutation at residue 132. An x-ray structure of the I132T/G134A double mutant protein (2.2-A resolution) showed that the changes in local structure were accompanied by a diffuse pattern of structural changes in the surrounding region, implying that the suppression derives from a combination of sources.

Amino Acid Sequence↗
PubMed1994

Identical mutations at corresponding positions in two homologous proteins with nonidentical effects.

The x-ray structure of a mutant (Gly72 to Asp) of the Escherichia coli ribose-binding protein with altered transport function has been solved and refined to 2.2-A resolution with a conventional R-factor (R-factor = [formula: see text]) of 16.0% and good stereochemistry. Comparison with the wild type ribose-binding protein shows that the structure is disturbed little at the actual mutation site, but quite appreciably in a neighboring loop. Changes in the surface of the protein at the site of mutation, however, seem to explain the functional effects. A corresponding mutation of the related glucose/galactose-binding protein has different structural and functional effects due to the different structural context of the mutation site in that protein. These results are consistent with the concept that these proteins have slightly different ways of interacting with the membrane components in transport and chemotaxis.

Amino Acid Sequence↗
PubMed1992

1.7 A X-ray structure of the periplasmic ribose receptor from Escherichia coli.

The X-ray structure of the periplasmic ribose receptor (binding protein) of Escherichia coli (RBP) was solved at 3 A resolution by the method of multiple isomorphous replacement. Alternating cycles of refitting and refinement have resulted in a model structure with an R-factor of 18.7% for 27,526 reflections from 7.5 to 1.7 A resolution (96% of the data). The model contains 2228 non-hydrogen atoms, including all 271 residues of the amino acid sequence, 220 solvent atoms and beta-D-ribose. The protein consists of two highly similar structural domains, each of which is composed of a core of parallel beta-sheet flanked on both sides by alpha-helices. The two domains are related to each other by an almost perfect 2-fold axis of rotation, with the C termini of the beta-strands of each sheet pointing toward the center of the molecule. Three short stretches of amino acid chain (from symmetrically related portions of the protein) link these two domains, and presumably act as a hinge to allow relative movement of the domains in functionally important conformational changes. Two water molecules are also an intrinsic part of the hinge, allowing crucial flexibility in the structure. The ligand beta-D-ribose (in the pyranose form) is bound between the domains, held by interactions with side-chains of the interior loops. The binding site is precisely tailored, with a combination of hydrogen bonding, hydrophobic and steric effects giving rise to tight binding (0.1 microM for ribose) and high specificity. Four out of seven binding-site residues are charged (2 each of aspartate and arginine) and contribute two hydrogen bonds each. The remaining hydrogen bonds are contributed by asparagine and glutamine residues. Three phenylalanine residues supply the hydrophobic component, packing against both faces of the sugar molecule. The arrangement of these hydrogen bonding and hydrophobic residues results in an enclosed binding site with the exact shape of the allowed sugar molecules; in the process of binding, the ligand loses all of its surface-accessible area. The sites of two mutations that affect the rate of folding of the ribose receptor are shown to be located near small cavities in the wild-type protein. The cavities thus allow the incorporation of the larger residues in the mutant proteins. Since these alterations would seriously affect the ability of the protein to build the first portion of the hydrophobic core in the first domain, it is proposed that this process is the rate-limiting step in folding of the ribose receptor.

Binding Sites↗
PubMed1990

Three-dimensional structure of thymidine phosphorylase from Escherichia coli at 2.8 A resolution.

The three-dimensional structure of thymidine phosphorylase from Escherichia coli has been determined at 2.8 A resolution using multiple-isomorphous-replacement techniques. The amino acid sequence deduced from the deoA DNA sequence is also reported. Thymidine phosphorylase exists in the crystal as an S-shaped dimer in which the subunits are related by a crystallographic 2-fold axis. Each subunit is composed of a small alpha-helical domain of six helices and a large alpha/beta domain. The alpha/beta domain includes a six-stranded mixed beta-sheet and a four-stranded antiparallel beta-sheet. The active site has been identified by difference Fourier analyses of the binding of thymine and thymidine and lies in a cavity between the small and large domains. The central beta-sheet is splayed open to accommodate a putative phosphate-binding site which is probably occupied by a sulfate ion in the crystal.

Amino Acid Sequence↗
PubMed1990

Preliminary X-ray data for the periplasmic ribose receptor from Escherichia coli.

Crystals of the periplasmic ribose receptor for chemotaxis and transport in Escherichia coli have been examined by X-ray analysis. The crystals grow as elongated rectangular prisms with the symmetry of the orthorhombic space group P2(1)2(1)2(1). The unit cell dimensions are a = 74.6 A, b = 88.8 A and c = 40.1 A. There is one molecule of molecular weight 28,500 per asymmetric unit.

Carrier Proteins↗
PubMed1990

Synthesis and crystal structures of Boc-L-Asn-L-Pro-OBzl.CH3OH and dehydration side product, Boc-beta-cyano-L-alanine-L-Pro-OBzl.

Boc-L-Asn-L-Pro-OBzl: C21H29O6N3.CH3OH, Mr = 419.48 + CH3 OH, monoclinic, P2(1), a = 10.049(1), b = 10.399(2), c = 11.702(1) A, beta = 92.50(1)degrees, V = 1221.7(3) A3, dx = 1.14 g.cm-3, Z = 2, CuK alpha (lambda = 1.54178 A), F(000) = 484 (with solvent), 23 degrees, unique reflections (I greater than 3 sigma(I)) = 1745, R = 0.043, Rw = 0.062, S = 1.66. Boc-beta-cyano-L-alanine-L-Pro-OBzl: C21H27O5N3, Mr = 401.46, orthorhombic, P2(1)2(1)2(1), a = 15.741(3), b = 21.060(3), c = 6.496(3) A, V = 2153(1) A3, dx = 1.24 g.cm-3, Z = 4, CuK alpha (lambda = 1.54178 A), F(000) = 856, 23 degrees, unique reflections (I greater than 3 sigma(I)) = 1573, R = 0.055, Rw = 0.078, S = 1.86. The tert.-butyloxycarbonyl (Boc) protected dipeptide benzyl ester (OBzl), Boc-L-Asn-L-Pro-OBzl, prepared from a mixed anhydride reaction using isobutylchloroformate, Boc-L-asparagine, and HCl.L-proline-OBzl, crystallized with one methanol per asymmetric unit in an extended conformation with the Asn-Pro peptide bond trans. Intermolecular hydrogen bonding occurs between the methanol and the Asn side chain and between the peptide backbone and the Asn side chain. A minor impurity due to the dehydration of the Asn side chain to a beta-CNala crystallized with a similar extended conformation and a single intermolecular hydrogen bond.

Amino Acid Sequence↗
PubMedDate not supplied

Structure of the periplasmic glucose/galactose receptor of Salmonella typhimurium.

The X-ray structure of the periplasmic glucose/galactose receptor (binding protein) of Salmonella typhimurium has been solved by the method of multiple isomorphous replacement and refined to a resolution of 2.4 A with an R-factor of 15.8%. The protein consists of two highly-similar structural domains with a bound sugar molecule trapped between. A combined sequence/structural approach is used to compare the structure of this protein to a similar arabinose receptor. The new sequence alignment obtained is used to analyze a number of features conserved for structural and functional reasons. This information allowed the prediction of similar features within the sequence of the analogous ribose receptor. Some of the consequences of the structures for chemotaxis and transport are discussed.

Amino Acid Sequence↗