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J Hixon

Publications and source records attributed to J Hixon.

8 recordsLinked to original sources
PubMed2001

Solution structure of B. subtilis acyl carrier protein.

BACKGROUND: Acyl carrier protein (ACP) is a fundamental component of fatty acid biosynthesis in which the fatty acid chain is elongated by the fatty acid synthetase system while attached to the 4'-phosphopantetheine prosthetic group (4'-PP) of ACP. Activation of ACP is mediated by holo-acyl carrier protein synthase (ACPS) when ACPS transfers the 4'-PP moiety from coenzyme A (CoA) to Ser36 of apo-ACP. Both ACP and ACPS have been identified as essential for E. coli viability and potential targets for development of antibiotics. RESULTS: The solution structure of B. subtilis ACP (9 kDa) has been determined using two-dimensional and three-dimensional heteronuclear NMR spectroscopy. A total of 22 structures were calculated by means of hybrid distance geometry-simulated annealing using a total of 1,050 experimental NMR restraints. The atomic rmsd about the mean coordinate positions for the 22 structures is 0.45 +/- 0.08 A for the backbone atoms and 0.93 +/- 0.07 A for all atoms. The overall ACP structure consists of a four alpha-helical bundle in which 4'-PP is attached to the conserved Ser36 that is located in alpha helix II. CONCLUSIONS: Structural data were collected for both the apo and holo forms of ACP that suggest that the two forms of ACP are essentially identical. Comparison of the published structures for E. coli ACP and actinorhodin polyketide synthase acyl carrier protein (act apo-ACP) from Streptomyces coelicolor A3(2) with B. subtilis ACP indicates similar secondary structure elements but an extremely large rmsd between the three ACP structures (>4.3 A). The structural difference between B. subtilis ACP and both E. coli and act apo-ACP is not attributed to an inherent difference in the proteins, but is probably a result of a limitation in the methodology available for the analysis for E. coli and act apo-ACP. Comparison of the structure of free ACP with the bound form of ACP in the ACP-ACPS complex reveals a displacement of helix II in the vicinity of Ser36. The induced perturbation of ACP by ACPS positions Ser36 proximal to coenzyme A and aligns the dipole of helix II to initiate transfer of 4'-PP to ACP.

Acyl Carrier Protein↗
PubMed2000

Crystal structures of substrate binding to Bacillus subtilis holo-(acyl carrier protein) synthase reveal a novel trimeric arrangement of molecules resulting in three active sites.

BACKGROUND: Holo-(acyl carrier protein) synthase (AcpS), a member of the phosphopantetheinyl transferase superfamily, plays a crucial role in the functional activation of acyl carrier protein (ACP) in the fatty acid biosynthesis pathway. AcpS catalyzes the attachment of the 4'-phosphopantetheinyl moiety of coenzyme A (CoA) to the sidechain of a conserved serine residue on apo-ACP. RESULTS: We describe here the first crystal structure of a type II ACP from Bacillus subtilis in complex with its activator AcpS at 2.3 A. We also have determined the structures of AcpS alone (at 1.8 A) and AcpS in complex with CoA (at 1.5 A). These structures reveal that AcpS exists as a trimer. A catalytic center is located at each of the solvent-exposed interfaces between AcpS molecules. Site-directed mutagenesis studies confirm the importance of trimer formation in AcpS activity. CONCLUSIONS: The active site in AcpS is only formed when two AcpS molecules dimerize. The addition of a third molecule allows for the formation of two additional active sites and also permits a large hydrophobic surface from each molecule of AcpS to be buried in the trimer. The mutations Ile5-->Arg, Gln113-->Glu and Gln113-->Arg show that AcpS is inactive when unable to form a trimer. The co-crystal structures of AcpS-CoA and AcpS-ACP allow us to propose a catalytic mechanism for this class of 4'-phosphopantetheinyl transferases.

Acyl Carrier Protein↗
PubMed2000

Differential effects of CD40 stimulation on normal and neoplastic cell growth.

CD40 is a molecule in the tumor necrosis factor receptor/nerve growth factor receptor (TNFR/NGFR) family that is present on both normal and neoplastic B lineage cells. It is also expressed on carcinoma and melanoma cells and can be augmented with interferon gamma. CD40 stimulation in normal B cells has been demonstrated to promote normal B cell differentiation and growth in vitro. In contrast to these effects, CD40 stimulation by either anti-CD40 antibodies or a recombinant soluble CD40 ligand can inhibit the growth of human breast carcinomas and aggressive histology B lymphomas in vitro and in vivo. This is believed to occur by activation-induced cell death (AICD) in which stimuli that promote the growth of normal cell types inhibit the growth of neoplastic counterparts. This occurs through the induction of apoptosis, necrosis and/or cell cycle arrest. Thus, CD40 stimulation may be of potential clinical use in the treatment of carcinomas and B cell lymphomas. This review shall provide an overview of the various effects of CD40 stimulation on both normal and neoplastic cell types.

Adenocarcinoma↗
PubMed1988

Long-lasting agonist activity produced by a capsaicin-like photoaffinity probe.

Capsaicin causes uptake of 45Ca2+ into a subset of neurons cultured from rat dorsal root ganglia. One aryl azido analogue of capsaicin produced a long-lasting stimulation of calcium uptake after irradiation in contact with cells, but not if samples were kept in the dark. The active compound, like capsaicin, is a 3-methoxy, 4-hydroxy benzylamide. An analogue without substitutions on the benzyl ring and one without the ring were not agonists. This pattern is consistent with known structure-activity relationships for capsaicin analogues. All three aryl azides produced long-lasting inhibition of capsaicin action, which was not totally dependent on irradiation. Long lasting agonist action was not produced if reversible capsaicin agonists were present as protecting ligands during the irradiation step. Potency as protectors correlated well with potency as agonists in the calcium uptake assay. We suggest that the active aryl azide is a photoaffinity label for a specific capsaicin receptor on dorsal root ganglion neurons but the inhibitory effects are not dependent on binding to the receptor.

Affinity Labels↗
PubMed1983

Effects of prostaglandins on the bovine corpus luteum: granules, lipid inclusions and progesterone secretion.

Corpora lutea collected at 15, 30 and 60 min after prostaglandin F2 alpha (PGF2 alpha) treatment were compared to control corpora lutea at 60 min after saline treatment. There were decreases (P less than 0.05) in the relative percentages of cytoplasm occupied by granules in large luteal cells (LLC) by 30 min and in small luteal cells (SLC) by 60 min. Differences were not observed among the groups for lipid inclusions. Luteal progesterone was decreased at all post-PGF2 alpha treatment times when compared to 60-min controls (P less than 0.05). PGF2 alpha was then compared with prostaglandin F1 alpha (PGF1 alpha), prostaglandin E1 (PGE1), and 17-phenyl-18,19,20-trinor-prostaglandin F2 alpha (17-phenyl-PGF2 alpha) in 60-min trials with plasma progesterone and luteinizing hormone (LH) determined every 5 min. LH was not affected by these treatments. Like PGF2 alpha, 17-phenyl-PGF2 alpha induced a greater loss of granules from LLC then SLC. 17-phenyl-PGF2 alpha also induced an increase in the lipid content of LLC. Treatments with PGF2 alpha and 17-phenyl-PGF2 alpha were associated with decreased concentrations of luteal progesterone but PGF1 alpha and PGE1 were without effect on this variable. In contrast to PGF1 alpha, PGE1 increased both luteal progesterone and the area occupied by cytoplasmic granules. The latter effect was greater in LLC than SLC.(ABSTRACT TRUNCATED AT 250 WORDS)

Alprostadil↗