Enhancement of salt tolerance in corn using Azospirillum brasilense: an approach on antioxidant systems

Journal of Plant Research - Salinity has become one of the major factors limiting agricultural production. In this regard, different cost-effective management strategies such as the use of plant...     

Xeroderma pigmentosum complementation group A protein is driven to nucleotide excision repair sites by the electrostatic potential of distorted DNA

The presumed DNA-binding cleft of xeroderma pigmentosum group A (XPA) protein, a key regulatory subunit of the eukaryotic nucleotide excision repair complex, displays a distinctive array of 6 positively charged amino acid side chains. Here, the molecular function of these closely spaced electropositive residues has been tested by systematic site-directed mutagenesis. After the introduction of single amino acid substitutions, the mutants were probed for protein-DNA interactions in electrophoretic mobility shift and photochemical crosslinking assays. This analysis led to the identification of a critical hot-spot for DNA substrate recognition composed of two neighboring lysines at codons 141 and 179 of the human XPA sequence. The replacement of other basic side chains in the DNA interaction domain conferred more moderate defects of substrate binding. When the function of XPA was tested as a fusion product with either mCherry or green-fluorescent protein, a glutamate substitution of one of the positively charged residues at positions 141 and 179 was sufficient to decrease DNA repair activity in human fibroblasts. Thus, the removal of a single cationic side chain abolished DNA-binding activity and significant excision repair defects could be induced by single charge inversions on the XPA surface, indicating that this molecular sensor participates in substrate recognition by monitoring the electrostatic potential of distorted DNA repair sites.     

SIR2-induced inviability is suppressed by histone H4 overexpression

We have identified histone H4 as a high-expression suppressor of Sir2-induced inviability in yeast cells. Overexpression of histone H3 does not suppress Sir2-induced lethality, nor does overexpression of histone H4 alleles associated with silencing defects. These results suggest a direct and specific interaction between Sir2 and H4 in the silencing mechanism.     

Lack of quinine-evoked activity in rat trigeminal subnucleus caudalis

Conflicting reports exist regarding the ability of quinine to activate neurons in the trigeminal system. We used the complementary approaches of single-unit electrophysiology and c-fos immunohistochemistry to investigate whether quinine (100 mM) activates chemonociceptive cells in the brainstem trigeminal subnucleus caudalis (Vc). In electrophysiological experiments, 38 units responded to noxious mechanical, thermal and chemical (200 mM pentanoic acid) stimuli applied to the tongue with an increase in firing rate; none responded to lingual quinine whether the quinine was presented before or after application of pentanoic acid. In the c-fos immunohistochemical experiment, both quinine and water elicited equivalent levels of fos-like immunoreactivity (FLI) in dorsomedial Vc that were significantly lower than the level of FLI evoked by pentanoic acid. These data collectively indicate that quinine does not elicit activity in chemonociceptive Vc neurons.     

MPB2C,a microtubule-associated plant protein binds to and interferes with cell-to-cell transport of tobacco mosaic virus movement protein

The movement protein of tobacco mosaic virus, MP30, mediates viral cell-to-cell transport via plasmodesmata. The complex MP30 intra- and intercellular distribution pattern includes localization to the endoplasmic reticulum, cytoplasmic bodies, microtubules, and plasmodesmata and likely requires interaction with plant endogenous factors. We have identified and analyzed an MP30-interacting protein, MPB2C, from the host plant Nicotiana tabacum. MPB2C constitutes a previously uncharacterized microtubule-associated protein that binds to and colocalizes with MP30 at microtubules. In vivo studies indicate that MPB2C mediates accumulation of MP30 at microtubules and interferes with MP30 cell-to-cell movement. In contrast, intercellular transport of a functionally enhanced MP30 mutant, which does not accumulate and colocalize with MP30 at microtubules, is not impaired by MPB2C. Together, these data support the concept that MPB2C is not required for MP30 cell-to-cell movement but may act as a negative effector of MP30 cell-to-cell transport activity.     

Antimicrobial Protegrin-1 Forms Ion Channels: Molecular Dynamic Simulation, Atomic Force Microscopy, and Electrical Conductance Studies

Antimicrobial peptides (AMPs) are an emerging class of antibiotics for controlling health effects of antibiotic-resistant microbial strains. Protegrin-1 (PG-1) is a model antibiotic among β-sheet AMPs. Antibiotic activity of AMPs involves cell membrane damage, yet their membrane interactions, their 3D membrane-associated structures and the mechanism underlying their ability to disrupt cell membrane are poorly understood. Using complementary approaches, including molecular dynamics simulations, atomic force microscopy (AFM) imaging, and planar lipid bilayer reconstitution, we provide computational and experimental evidence that PG-1, a β-hairpin peptide, forms ion channels. Simulations indicate that PG-1 forms channel-like structures with loosely attached subunits when reconstituted in anionic lipid bilayers. AFM images show the presence of channel-like structures when PG-1 is reconstituted in dioleoylphosphatidylserine/palmitoyloleoyl phosphatidylethanolamine bilayers or added to preformed bilayers. Planar lipid bilayer electrical recordings show multiple single channel conductances that are consistent with the heterogeneous oligomeric channel structures seen in AFM images. PG-1 channel formation seems to be lipid-dependent: PG-1 does not easily show ion channel electrical activity in phosphatidylcholine membranes, but readily shows channel activity in membranes rich in phosphatidylethanolamine or phosphatidylserine. The combined results support a model wherein the β-hairpin PG-1 peptide acts as an antibiotic by altering cell ionic homeostasis through ion channel formation in cell membranes.     

Disability life expectancy for the elderly, city of Sao Paulo, Brazil, 2000: gender and educational differences

There is evidence that 'health life expectancy' (expected number of years to be lived in health) differs by socioeconomic status. Time spent in health or disability plays a critical role in the use of health care services. The objective of this study was to estimate 'disability life expectancy' by age, gender and education attainment for the elderly of the city of S?o Paulo, Brazil, in the year 2000. Data came from the SABE database, population censuses and mortality statistics (SEADE Foundation). Life expectancy with disability was calculated using Sullivan's method on the basis of the current probability of death and prevalence of disability by educational level. The prevalence of disability increased with age, for both sexes and both levels of educational attainment studied. Men showed a lower prevalence of disability, in general, and persons with lower educational attainment showed a higher prevalence of disability. Regarding life expectancy, women could expect to live longer than men, with and without disability. For both sexes, the percentage of life expectancy lived with disability decreased with increasing educational attainment. With increasing educational attainment, the sex differences in the percentage of remaining years to be lived with disability increased for most ages. Finally, the percentage of remaining years to be lived with disability increased with age for males and females, except for males with high educational attainment between the ages 70-75 and 75-80. The results may serve as a guide for public policies in the country, since health problems faced by older persons, such as disability, are the result of a number of past experiences during their life-times, such as health care, housing conditions, hygiene practices and education. Education influences health behaviours and is related, to some extent, to all these factors. Therefore, improvements in education for the disadvantaged may improve health.     

Tarantula toxins interact with voltage sensors within lipid membranes

Voltage-activated ion channels are essential for electrical signaling, yet the mechanism of voltage sensing remains under intense investigation. The voltage-sensor paddle is a crucial structural motif in voltage-activated potassium (K(v)) channels that has been proposed to move at the protein-lipid interface in response to changes in membrane voltage. Here we explore whether tarantula toxins like hanatoxin and SGTx1 inhibit K(v) channels by interacting with paddle motifs within the membrane. We find that these toxins can partition into membranes under physiologically relevant conditions, but that the toxin-membrane interaction is not sufficient to inhibit K(v) channels. From mutagenesis studies we identify regions of the toxin involved in binding to the paddle motif, and those important for interacting with membranes. Modification of membranes with sphingomyelinase D dramatically alters the stability of the toxin-channel complex, suggesting that tarantula toxins interact with paddle motifs within the membrane and that they are sensitive detectors of lipid-channel interactions.