Effect of Virulence Factors on the Photodynamic Inactivation of Cryptococcus neoformans

Opportunistic fungal pathogens may cause an array of superficial infections or serious invasive infections, especially in immunocompromised patients. Cryptococcus neoformans is a pathogen causing cryptococcosis in HIV/AIDS patients, but treatment is limited due to the relative lack of potent antifungal agents. Photodynamic inactivation (PDI) uses the combination of non-toxic dyes called photosensitizers and harmless visible light, which produces singlet oxygen and other reactive oxygen species that produce cell inactivation and death. We report the use of five structurally unrelated photosensitizers (methylene blue, Rose Bengal, selenium derivative of a Nile blue dye, a cationic fullerene and a conjugate between poly-L-lysine and chlorin(e6)) combined with appropriate wavelengths of light to inactivate C. neoformans. Mutants lacking capsule and laccase, and culture conditions that favoured melanin production were used to probe the mechanisms of PDI and the effect of virulence factors. The presence of cell wall, laccase and melanin tended to protect against PDI, but the choice of the appropriate photosensitizers and dosimetry was able to overcome this resistance.Fundação de Amparo à Pesquisa do Estado de São Paulo (2010/13313–9

Calculation of the relative metastabilities of proteins in subcellular compartments of Saccharomyces cerevisiae

[abridged] Background: The distribution of chemical species in an open system at metastable equilibrium can be expressed as a function of environmental variables which can include temperature, oxidation-reduction potential and others. Calculations of metastable equilibrium for various model systems were used to characterize chemical transformations among proteins and groups of proteins found in different compartments of yeast cells. Results: With increasing oxygen fugacity, the relative metastability fields of model proteins for major subcellular compartments go as mitochondrion, endoplasmic reticulum, cytoplasm, nucleus. In a metastable equilibrium setting at relatively high oxygen fugacity, proteins making up actin are predominant, but those constituting the microtubule occur with a low chemical activity. A reaction sequence involving the microtubule and spindle pole proteins was predicted by combining the known intercompartmental interactions with a hypothetical program of oxygen fugacity changes in the local environment. In further calculations, the most-abundant proteins within compartments generally occur in relative abundances that only weakly correspond to a metastable equilibrium distribution. However, physiological populations of proteins that form complexes often show an overall positive or negative correlation with the relative abundances of proteins in metastable assemblages. Conclusions: This study explored the outlines of a thermodynamic description of chemical transformations among interacting proteins in yeast cells. The results suggest that these methods can be used to measure the degree of departure of a natural biochemical process or population from a local minimum in Gibbs energy.Comment: 32 pages, 7 figures; supporting information is available at http://www.chnosz.net/yeas

Substitued (E)-b-(benzoyl)acrylic acids suppressed survival of neoplastic human HeLa cells

The bacteriostatic activity of some of alkyl substituted (E)-b-(benzoyl)acrylic acids was shown earlier. The aim of this study was to investigate the antiproliferative action of 19 alkyl-, or halogeno-, or methoxy-, or acetamido- substituted (E)-b-(benzoyl)acrylic acids, against human cervix carcinoma, HeLa, cells. Target HeLa cells were continuously treated with increasing concentrations of substituted (E)-b-(benzoyl)acrylic acids during two days. The MTT test was used for assessment of the antiproliferative action of this group of compounds. Treatment of HeLa cells with 4-methyl-, 4-fluoro-, 4-chloro-, 4-bromo- and 4-methoxy- derivatives of (E)-b-(benzoyl) acrylic acid leads to the expression of cytostatic activity against HeLa cells (IC50 were in the range from 31-40 µM). Their antiproliferative action was less than that of the basic compound (E)-b-(benzoyl)acrylic acid whose IC50 was 28.5 µM. The 3,4-dimethyl-, 2,4-dimethyl- and 2,5-dimethyl- derivatives as well as the 4-ethyl- and 3,4-dichloro- and 2,4-dichloro-derivatives, have stronger cytostatic activity than the correspoding monosubstituted and parent compound. Their IC50 were 18.5 µM; 17.5 µM; 17.0 mM; 17.5 µM; 22.0 µM and 18 µM, respectively. The 4-iso-propyl- and 4-n-butyl-derivatives exerted higher cytostatic activity than the compounds with a lower number of methylene -CH2- groups in the substitutent. Their IC50 were 14.5 µM and 6.5 µM respectively. The 2,5-di-iso-propyl- and 4-tert-butyl-derivatives expressed the most strong antiproliferative action against the investigated HeLa cells, IC50 being 4.5 µM and 5.5 µM, respectively. The investigated compounds affected the survival of HeLa cells, expressing a strong structure-activity relationship of the Hansch type

Structural organization of human full-length PAR3 and the aPKC–PAR6 complex

The tripartite partition defect (PAR) polarity complex, which includes the proteins PAR3, atypical protein kinase C (aPKC), and PAR6, is a major regulator of cellular polarity. It is highly conserved and expressed in various tissues. Its largest component, PAR3, controls protein–protein interactions of the PAR complex with a variety of interaction partners, and PAR3 self-association is critical for the formation of filament-like structures. However, little is known about the structure of the PAR complex. Here, we purified non-filamentous PAR3 and the aPKC–PAR6 complex and characterized them by single-particle electron microscopy (EM). We expressed and purified an oligomerization-deficient form of PAR3, PAR3(V13D,D70K), and the active aPKC–PAR6 dimer. For PAR3, engineering at two positions is sufficient to form stable single particles with a maximum dimension of 20 nm. aPKC–PAR6 forms a complex with a maximum dimension of 13.5 nm that contains single copies of aPKC. Thus, the data present a basis for further high-resolution studies of PAR proteins and PAR complex formation. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s12033-022-00504-1

Sharing a host plant (wheat [Triticum aestivum]) increases the fitness of Fusarium graminiearum and the severity of fusarium head blight but reduces the fitness of grain aphids (Sitobion avenae)

We hypothesized that interactions between fusarium head blight-causing pathogens and herbivores are likely to occur because they share wheat as a host plant. Our aim was to investigate the interactions between the grain aphid, Sitobion avenae, and Fusarium graminearum on wheat ears and the role that host volatile chemicals play in mediating interactions. Wheat ears were treated with aphids and F. graminearum inoculum, together or separately, and disease progress was monitored by visual assessment and by quantification of pathogen DNA and mycotoxins. Plants exposed to both aphids and F. graminearum inoculum showed accelerated disease progression, with a 2-fold increase in disease severity and 5-fold increase in mycotoxin accumulation over those of plants treated only with F. graminearum. Furthermore, the longer the period of aphid colonization of the host prior to inoculation with F. graminearum, the greater the amount of pathogen DNA that accumulated. Headspace samples of plant volatiles were collected for use in aphid olfactometer assays and were analyzed by gas chromatography-mass spectrometry (GC-MS) and GC-coupled electroantennography. Disease-induced plant volatiles were repellent to aphids, and 2-pentadecanone was the key semiochemical underpinning the repellent effect. We measured aphid survival and fecundity on infected wheat ears and found that both were markedly reduced on infected ears. Thus, interactions between F. graminearum and grain aphids on wheat ears benefit the pathogen at the expense of the pest. Our findings have important consequences for disease epidemiology, because we show increased spread and development of host disease, together with greater disease severity and greater accumulation of pathogen DNA and mycotoxin, when aphids are present