Plasmid-encoded phthalate catabolic pathway in Arthrobacter keyseri 12B

Several 2-substituted benzoates (including 2-trifluoromethyl-, 2-chloro-, 2-bromo-, 2-iodo-, 2-nitro-, 2-methoxy-, and 2-acetyl-benzoates) were converted by phthalate-grown Arthrobacter keyseri (formerly Micrococcus sp.) 12B to the corresponding 2-substituted 3,4-dihydroxybenzoates (protocatechuates). Because these products lack a carboxyl group at the 2 position, they were not substrates for the next enzyme of the phthalate catabolic pathway, 3,4-dihydroxyphthalate 2-decarboxylase, and accumulated. When these incubations were carried out in iron-containing minimal medium, the products formed colored chelates. This chromogenic response was subsequently used to identify recombinant Escherichia coli strains carrying genes encoding the responsible enzymes, phthalate 3,4-dioxygenase and 3,4-dihydroxy-3,4-dihydrophthalate dehydrogenase, from the 130-kbp plasmid pRE1 of strain 12B. Beginning with the initially cloned 8.14-kbp PstI fragment of pRE824 as a probe to identify recombinant plasmids carrying overlapping fragments, a DNA segment of 33.5 kbp was cloned from pRE1 on several plasmids and mapped using restriction endonucleases. From these plasmids, the sequence of 26,274 contiguous bp was determined. Sequenced DNA included several genetic units: tnpR, pcm operon, ptr genes, pehA, norA fragment, and pht operon, encoding a transposon resolvase, catabolism of protocatechuate (3,4-dihydroxybenzoate), a putative ATP-binding cassette transporter, a possible phthalate ester hydrolase, a fragment of a norfloxacin resistance-like transporter, and the conversion of phthalate to protocatechuate, respectively. Activities of the eight enzymes involved in the catabolism of phthalate through protocatechuate to pyruvate and oxaloacetate were demonstrated in cells or cell extracts of recombinant E. coli strains.     

The role of T cell subsets and cytokines in the pathogenesis of Helicobacter pylori gastritis in mice

Gastritis due to Helicobacter pylori in mice and humans is considered a Th1-mediated disease, but the specific cell subsets and cytokines involved are still not well understood. The goal of this study was to investigate the immunopathogenesis of H. pylori-induced gastritis and delayed-type hypersensitivity (DTH) in mice. C57BL/6-Prkdc(scid) mice were infected with H. pylori and reconstituted with CD4+, CD4-depleted, CD4+CD45RB(high), or CD4+CD45RB(low) splenocytes from wild-type C57BL/6 mice or with splenocytes from C57BL/6(IFN-gamma-/-) or C57BL/6(IL-10-/-) mice. Four or eight weeks after transfer, DTH to H. pylori Ags was determined by footpad injection; gastritis and bacterial colonization were quantified; and IFN-gamma secretion by splenocytes in response to H. pylori Ag was determined. Gastritis and DTH were present in recipients of unfractionated splenocytes, CD4+ splenocytes, and CD4+CD45RB(high) splenocytes, but absent in the other groups. IFN-gamma secretion in response to H. pylori Ags was correlated with gastritis, although splenocytes from all groups of mice secreted some IFN-gamma. Gastritis was most severe in recipients of splenocytes from IL-10-deficient mice, and least severe in those given IFN-gamma-deficient splenocytes. Bacterial colonization in all groups was inversely correlated with gastritis. These data indicate that 1) CD4+ T cells are both necessary and sufficient for gastritis and DTH due to H. pylori in mice; 2) high expression of CD45RB is a marker for gastritis-inducing CD4+ cells; and 3) IFN-gamma contributes to gastritis and IL-10 suppresses it, but IFN-gamma secretion alone is not sufficient to induce gastritis. The results support the assertion that H. pylori is mediated by a Th1-biased cellular immune response.     

Association of sterol- and glycosylphosphatidylinositol-linked proteins with Drosophila raft lipid microdomains

In vertebrates, the formation of raft lipid microdomains plays an important part in both polarized protein sorting and signal transduction. To establish a system in which raft-dependent processes could be studied genetically, we have analyzed the protein and lipid composition of these microdomains in Drosophila melanogaster. Using mass spectrometry, we identified the phospholipids, sphingolipids, and sterols present in Drosophila membranes. Despite chemical differences between Drosophila and mammalian lipids, their structure suggests that the biophysical properties that allow raft formation have been preserved. Consistent with this, we have identified a detergent-insoluble fraction of Drosophila membranes that, like mammalian rafts, is rich in sterol, sphingolipids, and glycosylphosphatidylinositol-linked proteins. We show that the sterol-linked Hedgehog N-terminal fragment associates specifically with this detergent-insoluble membrane fraction. Our findings demonstrate that raft formation is preserved across widely separated phyla in organisms with different lipid structures. They further suggest sterol modification as a novel mechanism for targeting proteins to raft membranes and raise the possibility that signaling and polarized intracellular transport of Hedgehog are based on raft association.     

The ubiquity of avian ultraviolet plumage reflectance

Although several bird species have been shown to reflect ultraviolet (UV) light from their plumages, the incidence of UV reflectance, and therefore the potential for UV or UV-enhanced signals, across the avian tree of life is not known. In this study, we collected reflectance data from the plumages of 312 bird species representing 142 families. Our results demonstrate that all avian families possess plumages that reflect significant amounts of UV light. The ubiquity of UV reflectance indicates that all studies of avian behaviour, ecology and evolution involving plumage coloration would benefit from consideration of plumage reflectance in the UV portion of the electromagnetic spectrum. Additionally, we demonstrate the existence of cryptic UV plumage patches and cryptic dimorphism among birds.     

Experimental tests of villin subdomain folding simulations

We have used laser temperature-jump to investigate the kinetics and mechanism of folding the 35 residue subdomain of the villin headpiece. The relaxation kinetics are biphasic with a sub-microsecond phase corresponding to a helix-coil transition and a slower microsecond phase corresponding to overall unfolding/refolding. At 300 K, the folding time is 4.3(+/-0.6) micros, making it the fastest folding, naturally occurring protein, with a rate close to the theoretical speed limit. This time is in remarkable agreement with the prediction of 5 (+11,-3) micros by Zagrovic et al. from atomistic molecular dynamics simulations using an implicit solvent model. We test their prediction that replacement of the C-terminal phenylalanine residue with alanine will increase the folding rate by removing a transient non-native interaction. We find that the alanine substitution has no effect on the folding rate or on the equilibrium constant. Implications of this result for the validity of the simulated folding mechanism are discussed.