Biomedical subjects

W Furey

Publications and source records attributed to W Furey.

At least 19 recordsLinked to original sources

PubMed2001

Inhibition of the Escherichia coli pyruvate dehydrogenase complex E1 subunit and its tyrosine 177 variants by thiamin 2-thiazolone and thiamin 2-thiothiazolone diphosphates. Evidence for reversible tight-binding inhibition.

Variants of the pyruvate dehydrogenase subunit (E1; EC ) of the Escherichia coli pyruvate dehydrogenase multienzyme complex with Y177A and Y177F substitutions were created. Both variants displayed pyruvate dehydrogenase multienzyme complex activity at levels of 11% (Y177A E1) and 7% (Y177F E1) of the parental enzyme. The K(m) values for thiamin diphosphate (ThDP) were 1.58 microm (parental E1) and 6.65 microm (Y177A E1), whereas the Y177F E1 variant was not saturated at 200 microm. According to fluorescence studies, binding of ThDP was unaffected by the Tyr(177) substitutions. The ThDP analogs thiamin 2-thiazolone diphosphate (ThTDP) and thiamin 2-thiothiazolone diphosphate (ThTTDP) behaved as tight-binding inhibitors of parental E1 (K(i) = 0.003 microm for ThTDP and K(i) = 0.064 microm for ThTTDP) and the Y177A and Y177F variants. This analysis revealed that ThTDP and ThTTDP bound to parental E1 via a two-step mechanism, but that ThTDP bound to the Y177A variant via a one-step mechanism. Binding of ThTDP was affected and that of ThTTDP was unaffected by substitutions at Tyr(177). Addition of ThDP or ThTDP to parental E1 resulted in similar CD spectral changes in the near-UV region. In contrast, binding of ThTTDP to either parental E1 or the Y177A and Y177F variants was accompanied by the appearance of a positive band at 330 nm, indicating that ThTTDP was bound in a chiral environment. In combination with x-ray structural evidence on the location of Tyr(177), the kinetic and spectroscopic data suggest that Tyr(177) has a role in stabilization of some transition state(s) in the reaction pathway, starting with the free enzyme and culminating with the first irreversible step (decarboxylation), as well as in reductive acetylation of the dihydrolipoamide acetyltransferase component.

Amino Acid Sequence↗

PubMed2001

Structure of staphylococcal enterotoxin C2 at various pH levels.

The three-dimensional structure of staphylococcal enterotoxin C2 (SEC2), a toxin as well as a superantigen, has been determined at various pH levels from two different crystal forms, tetragonal (pH 5.0, 5.5, 6.0 and 6.5) and monoclinic (pH 8.0) at 100 and 293 K, respectively, by the molecular-replacement method. Tetragonal crystals belong to space group P4(3)2(1)2, with unit-cell parameters a = b = 42.68, c = 289.15 A (at pH 5.0), and monoclinic crystals to space group P2(1), with unit-cell parameters a = 43.3, b = 70.6, c = 42.2 A, beta = 90.3 degrees. SEC2 contains a zinc-binding motif, D+HExxH, and accordingly a Zn atom has been identified. The coordination of the zinc ion suggests that it may be catalytic zinc rather than structural, but there is so far no biological evidence that it possesses catalytic activity. However, superantigen staphylococcal exfoliative toxins A and B have been shown to have enzymatic activity after their fold was identified to be similar to that of serine protease. The structure and its conformation are similar to the previously reported structures of SEC2. Though it was expected that the zinc ion may be leached out, as the histidines coordinating the zinc ion are expected to be protonated below pH 6.0, zinc is present at all pH values. The coordination distances to zinc increase with decreasing pH, with the distances being the least at pH 8.0. The results of automated model building using the ARP/wARP program for different data sets collected at various pH values are discussed.

Bacterial Proteins↗

PubMed2001

Catalytic acid-base groups in yeast pyruvate decarboxylase. 1. Site-directed mutagenesis and steady-state kinetic studies on the enzyme with the D28A, H114F, H115F, and E477Q substitutions.

The roles of four of the active center groups with potential acid-base properties in the region of pH optimum of pyruvate decarboxylase from Saccharomyces cerevisiae have been studied with the substitutions Asp28Ala, His114Phe, His115Phe, and Glu477Gln, introduced by site-directed mutagenesis methods. The steady-state kinetic constants were determined in the pH range of activity for the enzyme. The substitutions result in large changes in k(cat) and k(cat)/S(0.5) (and related terms), indicating that all four groups have a role in transition state stabilization. Furthermore, these results also imply that all four are involved in some manner in stabilizing the rate-limiting transition state(s) both at low substrate (steps starting with substrate binding and culminating in decarboxylation) and at high substrate concentration (steps beginning with decarboxylation and culminating in product release). With the exception of some modest effects, the shapes of neither the bell-shaped k(cat)/S(0.5)-pH (and related functions) plots nor the k(cat)-pH plots are changed by the substitutions. Yet, the fractional activity still remaining after substitutions virtually rules out any of the four residues as being directly responsible for initiating the catalytic process by ionizing the C2H. There is no effect on the C2 H/D exchange rate exhibited by the D28A and E477Q substitutions. These results strongly imply that the base-induced deprotonation at C2 is carried out by the only remaining base, the iminopyrimidine tautomer of the coenzyme, via intramolecular proton abstraction. The first product is released as CO(2) rather than HCO(3)(-) by both wild-type and E477Q and D28A variants, ruling out several mechanistic alternatives.

Alanine↗

PubMed1999

Role of glutamate 91 in information transfer during substrate activation of yeast pyruvate decarboxylase.

Oligonucleotide-directed site-specific mutagenesis was carried out on pyruvate decarboxylase (EC 4.1.1.1) from Saccharomyces cerevisiae at E91, located on the putative substrate activation pathway and linking the alpha and gamma domains of the enzyme. While C221 on the beta domain is the residue at which substrate activation is triggered [Baburina, I., et al. (1994) Biochemistry 33, 5630-5635; Baburina, I., et al. (1996) Biochemistry 35, 10249-10255], that information, via the substrate bound at C221, is transmitted to H92 on the alpha domain, across the domain divide from C221 [Baburina, I. , et al. (1998) Biochemistry 37, 1235-1244], thence to E91 on the alpha domain, and then on to W412 on the gamma domain [Li, H., and Jordan, F. (1999) Biochemistry 38, 10004-10012] and to the active site thiamin diphosphate located at the interface of the alpha and gamma domains [Arjunan, D., et al. (1996) J. Mol. Biol. 256, 590-600]. Substitution at E91 with Q, D, or A led to modest reductions in the specific activity (4-, 5-, and 30-fold), as well as in both the turnover number and the catalytic efficiency, in that order. Interestingly, the Hill coefficient was only slightly reduced for the E91D variant, but cooperativity was virtually abolished for the E91Q and E91A variants. The thermal stability of the variants was reduced in the following order: wild type > E91Q > E91D > E91A; circular dichroism and fluorescence experiments also demonstrated that the tertiary structure of the enzyme was affected by these substitutions. The variants could be purified as apoenzymes, demonstrating their impaired ability to bind thiamin diphosphate. Apparently, the charge at residue 91 is quite important for maintaining optimal cooperativity. To maintain strong domain-domain interactions, the length of the side chain at position 91 with hydrogen bonding potential to W412 is sufficient.

Amino Acid Substitution↗

PubMed1998

Structure-function relationships and flexible tetramer assembly in pyruvate decarboxylase revealed by analysis of crystal structures.

The crystal structures of pyruvate decarboxylase from the yeast Saccharomyces uvarum and Saccharomyces cerevisiae have been determined at 2.4 and 2.3 A resolution, respectively. These structures provide details about the protein fold and domain assembly within subunits, about subunit assembly to form dimers and about dimer assembly to form tetramers. They also provide a clear picture of the active site centered on the thiamin diphosphate cofactor, and have allowed amino acids critical for catalysis and involved in stabilization of the unusual cofactor conformation to be identified. The structural information has enabled identification of the site of allosteric activation to be centered on Cys-221, and suggests that a six residue segment leading from the regulatory site to the catalytic site may be involved in transmission of a binding signal. The importance of several amino acids within this segment in the regulatory process, as well as some involved in stabilizing and activating the cofactor has been confirmed by analyzing the behavior of recombinant enzymes with single point mutations introduced at these sites. Additional structures have been determined for pyruvate decarboxylase in multiple crystal forms, some of which were obtained from crystals grown with known allosteric activators present in the media. Currently four distinct types of tetramers have been observed, with each showing a different mode of association of dimers to form the tetramers. In some of the cases involving the presence of allosteric activators drastic changes in the mode of dimer assembly to form tetramers is seen.

Allosteric Regulation↗

PubMed1998

Regulation of thiamin diphosphate-dependent 2-oxo acid decarboxylases by substrate and thiamin diphosphate.Mg(II) - evidence for tertiary and quaternary interactions.

The regulatory mechanism of substrate activation in yeast pyruvate decarboxylase is triggered by the interaction of pyruvic acid with C221 located on the beta domain at >20 A from the thiamin diphosphate (ThDP). To trace the putative information transfer pathway, substitutions were made at H92 on the alpha domain, across the domain divide from C221, at E91, next to H92 and hydrogen bonded to W412, the latter being intimately involved in the coenzyme binding locus. Additional substitutions were made at D28, E51, H114, H115, I415 and E477, all near the active center. The pH-dependent steady-state kinetic parameters, including the Hill coefficient, provide useful insight to this effort. In addition to C221, the residues H92, E91, E51 and H114 and H115 together appear to have a critical impact on the Hill coefficient, providing a pathway for information transfer. To study the activation by ThDP.Mg(II), variants at G231 (of the conserved GDG triplet) and at N258 and C259 (all three being part of the putative ThDP fold) of the E1 component of the Escherichia coli pyruvate dehydrogenase multienzyme complex were studied. Kinetic and spectroscopic evidence suggests that the Mg(II) ligands are very important to activation of the enzymes by cofactors.

Binding Sites↗

PubMed1998

Interdomain information transfer during substrate activation of yeast pyruvate decarboxylase: the interaction between cysteine 221 and histidine 92.

Oligonucleotide-directed site-specific mutagenesis was carried out on pyruvate decarboxylase (EC 4.1.1.1) from Saccharomyces cerevisiae at two cysteines on the beta domain (221 and 222) and at H92 on the alpha domain, across the domain divide from C221. While C221 has been shown to provide the trigger for substrate activation [Baburina, I., et al. (1994) Biochemistry 33, 5630-5635], the information must be transmitted from the substrate bound at this site [Arjunan, D., et al. (1996) J. Mol. Biol. 256, 590-600] to the active center thiamin diphosphate located at the interface of the alpha and gamma domains. Substitution at H92 with G, A, or C leads to great reduction of the Hill coefficient (from 2.0 in the wild-type enzyme to 1.2-1.3), while substitution for Lys affords an active enzyme with a Hill coefficient of 1.5-1.6. Iodoacetate at 10 mM reduced the Hill coefficient from 2.0 to 1.1, while also causing significant inactivation of the enzyme, presumably by carboxymethylation of C221. 1,3-Dibromoacetone, a potential cross-linker when added to the H92C/C222S variant at 0.1 mM, abolished substrate activation while reducing the activity only by 30%. Therefore, 1,3-dibromoacetone may cross-link C92 and C221. It was concluded that H92 is on the information transfer pathway during the substrate activation process and the interaction between C221 on the beta domain and H92 on the alpha domain is required for substrate activation. Extensive pH studies of the steady-state kinetic constants provide support for the interaction of C221 and H92 and the transmission of regulatory information to the active center via this pathway and pKaS for the two groups. This important interaction between the C221-bound pyruvate and His92 probably has both electrostatic and steric components.

Cysteine↗

PubMed1997

Mutations in the cationic trypsinogen gene are associated with recurrent acute and chronic pancreatitis.

BACKGROUND & AIMS: We recently identified a single R117H mutation in the cationic trypsinogen gene in several kindreds with an inherited form of acute and chronic pancreatitis (HP1), providing strong evidence that trypsin plays a central role in premature zymogen activation and pancreatitis. However, not all families studied have this mutation. The aim of this study was to determine the disease-causing mutation in kindreds with hereditary pancreatitis that lack the previously identified mutation. METHODS: Clinical features of the HP1 kindreds were compared with those of the new kindreds (HP2), and genetic linkage analysis, screening for mutations through DNA sequencing, and screening an unaffected population were performed. RESULTS: The onset of symptoms was delayed and hospitalizations were fewer in HP2 compared with HP1 (P < 0.05). Linkage of the disease gene to chromosome 7q35 was established (logarithm of the odds, 3.73). Mutational screening identified a single A to T mutation resulting in an asparagine to isoleucine transition mutation at position 21 (N21I) in cationic trypsinogen. The mutation was absent in 94 unrelated individuals, representing 188 unique chromosomes. CONCLUSIONS: The identification of a second mutation in the cationic trypsinogen gene (HP2) suggests a dominant role of trypsin in premature protease activation-mediated forms of acute pancreatitis. The pathogenesis of hereditary pancreatitis also suggests that chronic pancreatitis may result from recurrent acute pancreatitis.

Acute Disease↗

PubMed1996

Crystal structure of the thiamin diphosphate-dependent enzyme pyruvate decarboxylase from the yeast Saccharomyces cerevisiae at 2.3 A resolution.

The crystal structure of pyruvate decarboxylase (EC 4.1.1.1), a thiamin diphosphate-dependent enzyme isolated from Saccharomyces cerevisiae, has been determined and refined to a resolution of 2.3 A. Pyruvate decarboxylase is a homotetrameric enzyme which crystallizes with two subunits in an asymmetric unit. The structure has been refined by a combination of simulated annealing and restrained least squares to an R factor of 0.165 for 46,787 reflections. As in the corresponding enzyme from Saccharomyces uvarum, the homotetrameric holoenzyme assembly has approximate 222 symmetry. In addition to providing more accurate atomic parameters and certainty in the sequence assignments, the high resolution and extensive refinement resulted in the identification of several tightly bound water molecules in key structural positions. These water molecules have low temperature factors and make several hydrogen bonds with protein residues. There are six such water molecules in each cofactor binding site, and one of them is involved in coordination with the required magnesium ion. Another may be involved in the catalytic reaction mechanism. The refined model includes 1074 amino acid residues (two subunits), two thiamin diphosphate cofactors, two magnesium ions associated with cofactor binding and 440 water molecules. From the refined model we conclude that the resting state of the enzyme-cofactor complex is such that the cofactor is already deprotonated at the N4' position of the pyrimidine ring, and is poised to accept a proton from the C2 position of the thiazolium ring.

Amino Acid Sequence↗

PubMed1996

Hereditary pancreatitis is caused by a mutation in the cationic trypsinogen gene.

Hereditary pancreatitis (HP) is a rare, early-onset genetic disorder characterized by epigastric pain and often more serious complications. We now report that an Arg-His substitution at residue 117 of the cationic trypsinogen gene is associated with the HP phenotype. This mutation was observed in all HP affected individuals and obligate carriers from five kindreds, but not in individuals who married into the families nor in 140 unrelated individuals. X-ray crystal structure analysis, molecular modelling, and protein digest data indicate that the Arg 117 residue is a trypsin-sensitive site. Cleavage at this site is probably part of a fail-safe mechanism by which trypsin, which is activated within the pancreas, may be inactivated; loss of this cleavage site would permit autodigestion resulting in pancreatitis.

Arginine↗

PubMed1995

Preliminary X-ray studies on two new crystal forms of staphylococcal enterotoxin C2.

Two new crystal forms of staphylococcal enterotoxin C2 have been obtained by vapor-diffusion methods. Form 1 crystals are monoclinic in space group P2(1) with cell dimensions a = 43.43, b = 69.92, c = 42.22 A, 8 = 90.1 degrees and diffract to at least 2.7 A resolution. Form 2 crystals are tetragonal in space group P4(1)2(1)2 or P4(3)2(1)2 with cell dimensions a = b = 42.98, c = 289.92 A and diffract to 1.9 A resolution.

Journal Article↗

PubMed1995

Crystal structure of the DNA-binding domain of the Epstein-Barr virus origin-binding protein EBNA 1.

The crystal structure of the DNA-binding and dimerization domains of the Epstein-Barr virus nuclear antigen 1 (EBNA1), which binds to and activates DNA replication from the latent origin of replication in Epstein-Barr virus, was solved at 2.5 A resolution. EBNA1 appears to bind DNA via two independent regions termed the core and the flanking DNA-binding domains. The core DNA-binding domain, which comprises both the dimerization domain and a helix predicted to bind the inner portion of the EBNA1 DNA recognition element, was remarkably similar to the structure of the papillomavirus E2 protein, despite a complete lack of sequence conservation. The flanking DNA-binding domain, only a portion of which is contained in the current structure, consists in part of an alpha helix whose N-terminus contacts the outer regions of the EBNA1 DNA recognition element.

Amino Acid Sequence↗

PubMed1995

Crystallization and preliminary analysis of two crystal forms of human clara cell 16 kDa protein (CC10).

The human Clara cell 16 kDa protein (CC10), isolated from lung lavage fluid, has been crystallized in two crystal forms. The first is in space group P1 and has cell parameters a = 43.04, b = 45.90, c = 51.29 A and alpha = 62.46, beta = 69.74, gamma = 69.43 degrees. Two molecules are present in the unit cell. The second form is in space group P222, with cell parameters a = 42.24, b = 84.06, c = 40.05 A and alpha = beta = gamma = 90 degrees, and four molecules per unit cell. Its diffraction pattern displays pseudo-body-centered symmetry. Both crystal forms diffract X-rays beyond 2.0 A.

Journal Article↗

PubMed1995

Residues defining V beta specificity in staphylococcal enterotoxins.

The three-dimensional structure of staphylococcal enterotoxin C2 has been determined at 2.7 A resolution by x-ray diffraction, while the structures of enterotoxins A and E have been modelled based on their sequence homology to other staphylococcal enterotoxins. The T-cell receptor-binding sites of staphylococcal enterotoxin (SE) B and SEC2 are compared and the stereochemical interactions likely to be responsible for their differing V beta specificities are identified. A similar comparison is made between SEA and SEE.

Amino Acid Sequence↗

PubMed1994

Substrate activation of brewers' yeast pyruvate decarboxylase is abolished by mutation of cysteine 221 to serine.

Brewers' yeast pyruvate decarboxylase (EC 4.1.1.1), a thiamin diphosphate and Mg(II)-dependent enzyme, isolated from Saccharomyces cerevisiae possesses four cysteines/subunit at positions 69, 152, 221, and 222. Earlier studies conducted on a variant of the enzyme with a single Cys at position 221 (derived from a gene that was the product of spontaneous fusion) showed that this enzyme is still subject to substrate activation [Zeng, X., Farrenkopf, B., Hohmann, S., Jordan, F., Dyda, F., & Furey, W. (1993) Biochemistry 32, 2704-2709], indicating that if Cys was responsible for this activation, it had to be C221. To further test the hypothesis, the C221S and C222S single and the C221S-C222S double mutants were constructed. It is clearly shown that the mutation at C221, but not at C222, leads to abolished substrate activation according to a number of kinetic criteria, both steady state and pre steady state. On the basis of the three-dimensional structure of the enzyme [Dyda, F., Furey, W., Swaminathan, S., Sax, M., Farrenkopf, B., Jordan, F. (1993) Biochemistry 32, 6165-6170], it is obvious that while C221 is located on the beta domain, whereas thiamin diphosphate is wedged at the interface of the alpha and gamma domains, addition of pyruvate or pyruvamide as a hemiketal adduct to the sulfur of C221 can easily bridge the gap between the beta and alpha domains. In fact, residues in one or both domains must be dislocated by this adduct formation. It is very likely that regulation as expressed in substrate activation is transmitted via this direct contact made between the two domains in the presence of the activator.(ABSTRACT TRUNCATED AT 250 WORDS)

Base Sequence↗

PubMed1994

Structure of a human Clara cell phospholipid-binding protein-ligand complex at 1.9 A resolution.

The Clara cell phospholipid-binding protein, previously referred to as CC10, is a homodimeric protein of M(r) 15,800. It is secreted into the bronchioalveolar lining layer in mammalian lung. A combination of X-ray crystallography and chemical analysis was used to determine that phosphatidylcholine and phosphatidylinositol are bound to the protein as isolated from human lung lavage. We now report the crystal structure of the protein-phospholipid complex at 1.9 A resolution. The phospholipid is bound inside the protein's large hydrophobic cavity. A model is proposed for the manner in which a channel may open to provide access to the cavity, allowing the binding or potential release of phospholipid.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1993

A thiamin diphosphate binding fold revealed by comparison of the crystal structures of transketolase, pyruvate oxidase and pyruvate decarboxylase.

BACKGROUND: The crystal structures of three thiamin diphosphate-dependent enzymes that catalyze distinct reactions in basic metabolic pathways are known. These enzymes--transketolase, pyruvate oxidase and pyruvate decarboxylase--also require metal ions such as Ca2+ and Mg2+ as cofactors and have little overall sequence similarity. Here, the crystal structures of these three enzymes are compared. RESULTS: The three enzymes share a similar pattern of binding of thiamin diphosphate and the metal ion cofactors. The enzymes function as multisubunit proteins, with each polypeptide chain folded into three alpha/beta domains. Two of these domains are involved in binding of the thiamin diphosphate and the metal ion. These domains have the same topology of six parallel beta-strands and surrounding alpha-helices. The thiamin diphosphate is bound in a cleft, formed by two domains from two different subunits. Only a few residues are conserved in all three enzymes and these are responsible for proper binding of the cofactors. CONCLUSIONS: Despite considerable differences in quaternary structure and lack of overall sequence homology, thiamin diphosphate binds to the three enzymes in a very similar fashion, and a general thiamin-binding fold can be revealed.

Amino Acid Sequence↗

PubMed1993

Catalytic centers in the thiamin diphosphate dependent enzyme pyruvate decarboxylase at 2.4-A resolution.

The crystal structure of brewers' yeast pyruvate decarboxylase, a thiamin diphosphate dependent alpha-keto acid decarboxylase, has been determined to 2.4-A resolution. The homotetrameric assembly contains two dimers, exhibiting strong intermonomer interactions within each dimer but more limited ones between dimers. Each monomeric subunit is partitioned into three structural domains, all folding according to a mixed alpha/beta motif. Two of these domains are associated with cofactor binding, while the other is associated with substrate activation. The catalytic centers containing both thiamin diphosphate and Mg(II) are located deep in the intermonomer interface within each dimer. Amino acids important in cofactor binding and likely to participate in catalysis and substrate activation are identified.

Binding Sites↗