716 research outputs found
Characterization of the PMT Gene Family in Cryptococcus neoformans
BACKGROUND:Protein-O-mannosyltransferases (Pmt's) catalyze the initial step of protein-O-glycosylation, the addition of mannose residues to serine or threonine residues of target proteins. METHODOLOGY/PRINCIPAL FINDINGS:Based on protein similarities, this highly conserved protein family can be divided into three subfamilies: the Pmt1 sub-family, the Pmt2 sub-family and the Pmt4 sub-family. In contrast to Saccharomyces cerevisiae and Candida albicans, but similar to filamentous fungi, three putative PMT genes (PMT1, PMT2, and PMT4) were identified in the genome of the human fungal pathogen Cryptococcus neoformans. Similar to Schizosaccharomyces pombe and C. albicans, C. neoformans PMT2 is an essential gene. In contrast, the pmt1 and pmt4 single mutants are viable; however, the pmt1/pmt4 deletions are synthetically lethal. Mutation of PMT1 and PMT4 resulted in distinct defects in cell morphology and cell integrity. The pmt1 mutant was more susceptible to SDS medium than wild-type strains and the mutant cells were enlarged. The pmt4 mutant grew poorly on high salt medium and demonstrated abnormal septum formation and defects in cell separation. Interestingly, the pmt1 and pmt4 mutants demonstrated variety-specific differences in the levels of susceptibility to osmotic and cell wall stress. Delayed melanin production in the pmt4 mutant was the only alteration of classical virulence-associated phenotypes. However, the pmt1 and pmt4 mutants showed attenuated virulence in a murine inhalation model of cryptococcosis. CONCLUSION/SIGNIFICANCE:These findings suggest that C. neoformans protein-O-mannosyltransferases play a crucial role in maintaining cell morphology, and that reduced protein-O-glycosylation leads to alterations in stress resistance, cell wall composition, cell integrity, and survival within the host
A new mechanism for electron spin echo envelope modulation
Electron spin echo envelope modulation (ESEEM) has been observed for the
first time from a coupled hetero-spin pair of electron and nucleus in liquid
solution. Previously, modulation effects in spin echo experiments have only
been described in liquid solutions for a coupled pair of homonuclear spins in
NMR or a pair of resonant electron spins in EPR. We observe low-frequency ESEEM
(26 and 52 kHz) due to a new mechanism present for any electron spin with S>1/2
that is hyperfine coupled to a nuclear spin. In our case these are electron
spin (S=3/2) and nuclear spin (I=1) in the endohedral fullerene N@C60. The
modulation is shown to arise from second order effects in the isotropic
hyperfine coupling of an electron and 14N nucleus.Comment: 15 pages, 4 figure
Do Researchers Anchor their Beliefs on the Outcome of an Initial Study? Testing the Time-Reversal Heuristic
As a research field expands, scientists have to update their knowledge and integrate the outcomes of a sequence of studies. However, such integrative judgments are generally known to fall victim to a primacy bias where people anchor their judgments on the initial information. In this preregistered study we tested the hypothesis that people anchor on the outcome of a small initial study, reducing the impact of a larger subsequent study that contradicts the initial result. Contrary to our expectation, undergraduates and academics displayed a recency bias, anchoring their judgment on the research outcome presented last. This recency bias is due to the fact that unsuccessful replications decreased trust in an effect more than did unsuccessful initial experiments. We recommend the time-reversal heuristic to account for temporal order effects during integration of research results
Dynamics of Quasi-ordered Structure in a Regio-regulated pi-Conjugated Polymer:Poly(4-methylthiazole-2,5-diyl)
Dynamics of regio-regulated Poly(4-methylthiazole-2,5-diyl) [HH-P4MeTz] was
inves tigated by solid-state 1H, 2D, 13C NMR spectroscopies, and differential
scanning calorimetry(DSC) measurements. DSC, 2D quadrupolar echo NMR, 13C
cross-polarization and magic-angle spinning(CPMAS) NMR, and 2D spin-echo(2DSE)
CPMAS NMR spectroscopy suggest existence of a quasi-ordered phase in which
backbone twists take place with weakened pi-stackings. Two-dimensional exchange
2D NMR(2DEX) detected slow dynamics with a rate of an order of 10^2Hz for the
CD_3 group in d_3-HH-P4MeTz at 288K. The frequency dependence of proton
longitudinal relaxation rate at 288K shows a omega^-1/2 dependence, which is
due to the one-dimensional diffusion-like motion of backbone conformational
modulation waves. The diffusion rate was estimated as 3+/-2 GHz, which was
approximately 10^7 times larger than that estimated by 2DEX NMR measurements.
These results suggest that there exists anomalous dispersion of modulation
waves in HH-P4MeTz. The one-dimensional group velocity of the wave packet is
responsible for the behavior of proton longitudinal relaxation time. On the
other hand, the 2DEX NMR is sensitive to phase velocity of the nutation of
methyl groups that is associated with backbone twists. From proton T_1 and T_2
measurements, the activation energy was estimated as 2.9 and 3.4 kcal/mol,
respectively. These were in agreement with 3.0 kcal/mol determined by
Moller-Plesset(MP2) molecular orbital(MO) calculation. We also performed
chemical shielding calculation of the methyl-carbon in order to understand
chemical shift tensor behavior, leading to the fact that a quasi-ordered phase
coexist with the crystalline phase.Comment: 14 pages, 11 figures, to appear in Phys.Rev.
Mutation of Tyr137 of the universal Escherichia coli fimbrial adhesin FimH relaxes the tyrosine gate prior to mannose binding
The most prevalent diseases manifested by Escherichia coli are acute and recurrent bladder infections and chronic inflammatory bowel diseases such as Crohn's disease. E. coli clinical isolates express the FimH adhesin, which consists of a mannose-specific lectin domain connected via a pilin domain to the tip of type 1 pili. Although the isolated FimH lectin domain has affinities in the nanomolar range for all high-mannosidic glycans, differentiation between these glycans is based on their capacity to form predominantly hydrophobic interactions within the tyrosine gate at the entrance to the binding pocket. In this study, novel crystal structures of tyrosine-gate mutants of FimH, ligand-free or in complex with heptyl α - D - O -mannopyranoside or 4-biphenyl α - D - O- mannopyranoside, are combined with quantum-mechanical calculations and molecular-dynamics simulations. In the Y48A FimH crystal structure, a large increase in the dynamics of the alkyl chain of heptyl α - D - O -mannopyranoside attempts to compensate for the absence of the aromatic ring; however, the highly energetic and stringent mannose-binding pocket of wild-type FimH is largely maintained. The Y137A mutation, on the other hand, is the most detrimental to FimH affinity and specificity: (i) in the absence of ligand the FimH C-terminal residue Thr158 intrudes into the mannose-binding pocket and (ii) ethylenediaminetetraacetic acid interacts strongly with Glu50, Thr53 and Asn136, in spite of multiple dialysis and purification steps. Upon mutation, pre-ligand-binding relaxation of the backbone dihedral angles at position 137 in the tyrosine gate and their coupling to Tyr48 via the interiorly located Ile52 form the basis of the loss of affinity of the FimH adhesin in the Y137A mutant
Nucleating Black Holes via Non-Orientable Instantons
We extend the analysis of black hole pair creation to include non- orientable
instantons. We classify these instantons in terms of their fundamental
symmetries and orientations. Many of these instantons admit the pin structure
which corresponds to the fermions actually observed in nature, and so the
natural objection that these manifolds do not admit spin structure may not be
relevant. Furthermore, we analyse the thermodynamical properties of
non-orientable black holes and find that in the non-extreme case, there are
interesting modifications of the usual formulae for temperature and entropy.Comment: 27 pages LaTeX, minor typos are correcte
Entropy in Black Hole Pair Production
Pair production of Reissner-Nordstrom black holes in a magnetic field can be
described by a euclidean instanton. It is shown that the instanton amplitude
contains an explicit factor of , where is the area of the event
horizon. This is consistent with the hypothesis that measures the
number of black hole states.Comment: 24 pages (harvmac l mode
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