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P Yorgey

Publications and source records attributed to P Yorgey.

6 recordsLinked to original sources
PubMed2001

The roles of mucD and alginate in the virulence of Pseudomonas aeruginosa in plants, nematodes and mice.

We are exploiting the broad host range of the human opportunistic pathogen Pseudomonas aeruginosa strain PA14 to elucidate the molecular basis of bacterial virulence in plants, nematodes, insects and mice. In this report, we characterize the role that two PA14 gene products, MucD and AlgD, play in virulence. MucD is orthologous to the Escherichia coli periplasmic protease and chaperone DegP. DegP homologues are known virulence factors that play a protective role in stress responses in various species. AlgD is an enzyme involved in the biosynthesis of the exopolysaccharide alginate, which is hyperinduced in mucD mutants. A PA14 mucD mutant was significantly impaired in its ability to cause disease in Arabidopsis thaliana and mice and to kill the nematode Caenorhabditis elegans. Moreover, MucD was found to be required for the production of an extracellular toxin involved in C. elegans killing. In contrast, a PA14 algD mutant was not impaired in virulence in plants, nematodes or mice. A mucDalgD double mutant had the same phenotype as the mucD single mutant in the plant and nematode pathogenesis models. However, the mucDalgD double mutant was synergistically reduced in virulence in mice, suggesting that alginate can partially compensate for the loss of MucD function in mouse pathogenesis.

Alginates↗
PubMed2000

Salmonella typhimurium proliferates and establishes a persistent infection in the intestine of Caenorhabditis elegans.

Genetic analysis of host-pathogen interactions has been hampered by the lack of genetically tractable models of such interactions. We showed previously that the human opportunistic pathogen Pseudomonas aeruginosa kills Caenorhabditis elegans, that P. aeruginosa and C. elegans genes can be identified that affect this killing, and that most of these P. aeruginosa genes are also important for mammalian pathogenesis. Here, we show that Salmonella typhimurium as well as other Salmonella enterica serovars including S. enteritidis and S. dublin can also kill C. elegans. When C. elegans is placed on a lawn of S. typhimurium, the bacteria accumulate in the lumen of the worm intestine and the nematodes die over the course of several days. This killing requires contact with live bacterial cells. The worms die with similar kinetics when placed on a lawn of S. typhimurium for a relatively short time (3-5 hours) before transfer to a lawn of E. coli. After the transfer to E. coli, a high titer of S. typhimurium persists in the C. elegans intestinal lumen for the rest of the worms' life. Furthermore, feeding for 5 hours on a 1:1000 mixture of S. typhimurium and E. coli followed by transfer to 100% E. coli, also led to death after several days. This killing correlated with an increase in the titer of S. typhimurium in the C. elegans lumen, which reached 10,000 bacteria per worm. These data indicate that, in contrast to P. aeruginosa, a small inoculum of S. typhimurium can proliferate in the C. elegans intestine and establish a persistent infection. S. typhimurium mutated in the PhoP/PhoQ signal transduction system caused significantly less killing of C. elegans.

Animals↗
PubMed2000

Fumonisin B1-induced cell death in arabidopsis protoplasts requires jasmonate-, ethylene-, and salicylate-dependent signaling pathways.

We have established an Arabidopsis protoplast model system to study plant cell death signaling. The fungal toxin fumonisin B1 (FB1) induces apoptosis-like programmed cell death (PCD) in wild-type protoplasts. FB1, however, only marginally affects the viability of protoplasts isolated from transgenic NahG plants, in which salicylic acid (SA) is metabolically degraded; from pad4-1 mutant plants, in which an SA amplification mechanism is thought to be impaired; or from jar1-1 or etr1-1 mutant plants, which are insensitive to jasmonate (JA) or ethylene (ET), respectively. FB1 susceptibility of wild-type protoplasts decreases in the dark, as does the cellular content of phenylalanine ammonia-lyase, a light-inducible enzyme involved in SA biosynthesis. Interestingly, however, FB1-induced PCD does not require the SA signal transmitter NPR1, given that npr1-1 protoplasts display wild-type FB1 susceptibility. Arabidopsis cpr1-1, cpr6-1, and acd2-2 protoplasts, in which the SA signaling pathway is constitutively activated, exhibit increased susceptibility to FB1. The cpr6-1 and acd2-2 mutants also constitutively express the JA and ET signaling pathways, but only the acd2-2 protoplasts undergo PCD in the absence of FB1. These results demonstrate that FB1 killing of Arabidopsis is light dependent and requires SA-, JA-, and ET-mediated signaling pathways as well as one or more unidentified factors activated by FB1 and the acd2-2 mutation.

Arabidopsis↗
PubMed1994

Posttranslational modifications in microcin B17 define an additional class of DNA gyrase inhibitor.

Drugs that inhibit the activity of DNA gyrase fall almost exclusively into two structural classes, the quinolones and the coumarins. A third class of DNA gyrase inhibitor is defined by the ribosomally synthesized peptide antibiotic microcin B17 (MccB17). MccB17 contains 43 amino acid residues, but 14 of these are posttranslationally modified. Here we describe the characterization of the structure of these modifications. We propose that four cysteine and four serine side chains undergo condensation with the carbonyl group of the preceding residue, followed by alpha/beta dehydrogenation to yield four thiazole and four oxazole rings, respectively. The three proteins implicated in catalyzing these modifications (McbBCD) would constitute the only thiazole/oxazole biosynthetic enzymes identified. These results open up possibilities for the design of DNA gyrase inhibitors and add to the repertoire of posttranslational modifications with potential for protein engineering. Escherichia coli sbmA mutants, which lack the inner membrane protein (SbmA) involved in MccB17 uptake, were found to be resistant to bleomycin. Bleomycin is structurally unrelated to MccB17 except for the fact that it contains two thiazole rings. This suggests that thiazole rings are part of the MccB17 structure recognized by SbmA. This observation and the finding that SbmA homologs are widely conserved and can play developmental roles [Glazebrook, J., Ichige, A. & Walker, G. C. (1993) Genes Dev. 7, 1485-1497] suggest that thiazole- and oxazole-containing compounds may serve as signaling molecules for a wide variety of bacteria in diverse environments, including pathogen interactions with plant and animal hosts.

Amino Acid Sequence↗
PubMed1993

The maturation pathway of microcin B17, a peptide inhibitor of DNA gyrase.

The maturation pathway of microcin B17 (MccB17), a ribosomally synthesized peptide antibiotic which inhibits DNA gyrase, has been characterized. Synthesis of MccB17 involves several steps beginning with the translation of the MccB17 structural gene, mcbA, to yield a 69 amino acid precursor, preMccB17. Pre-MccB17 is then modified and folded by the action of three gene products, McbBCD, to yield proMccB17. Mutations in mcbA were isolated that permit modifications of the resulting mutant peptides, but prevent folding, suggesting that modification and folding are sequential steps. ProMccB17 is subsequently converted to MccB17 by removal of the N-terminal 26-amino-acid leader by a chromosomally encoded protease. Removal of the leader resulted in aggregation of the peptide, suggesting that the leader may function to maintain peptide solubility during synthesis in the cell. Finally, polyclonal antibodies raised against MccB17 recognize both MccB17 and proMccB17, but do not recognize preMccB17. This demonstrates the dramatic structural changes that result from the modifications and has been used to distinguish intermediates in the steps of maturation.

Amino Acid Sequence↗