Molecular basis of proton blockage in aquaporins

Water transport channels in membrane proteins of the aquaporin superfamily are impermeable to ions, including H+ and OH-. We examine the molecular basis for the blockage of proton translocation through the single-file water chain in the pore of a bacterial aquaporin, GlpF. We compute the reversible thermodynamic work for the two complementary steps of the Grotthuss "hop-and-turn" relay mechanism: consecutive transfers of H+ along the hydrogen-bonded chain (hop) and conformational reorganization of the chain (turn). In the absence of H+, the strong preference for the bipolar orientation of water around the two Asn-Pro-Ala (NPA) motifs lining the pore over both unidirectional polarization states of the chain precludes the reorganization of the hydrogen-bonded network. Inversely, translocation of an excess proton in either direction is opposed by a free-energy barrier centered at the NPA region. Both hop and turn steps of proton translocation are opposed by the electrostatic field of the channel.     

Segregation of Lexical and Sub-Lexical Reading Processes in the Left Perisylvian Cortex

A fundamental issue in cognitive neuroscience is the existence of two major, sub-lexical and lexical, reading processes and their possible segregation in the left posterior perisylvian cortex. Using cortical electrostimulation mapping, we identified the cortical areas involved on reading either orthographically irregular words (lexical, “direct” process) or pronounceable pseudowords (sublexical, “indirect” process) in 14 right-handed neurosurgical patients while video-recording behavioral effects. Intraoperative neuronavigation system and Montreal Neurological Institute (MNI) stereotactic coordinates were used to identify the localization of stimulation sites. Fifty-one reading interference areas were found that affected either words (14 areas), or pseudo-words (11 areas), or both (26 areas). Forty-one (80%) corresponded to the impairment of the phonological level of reading processes. Reading processes involved discrete, highly localized perisylvian cortical areas with individual variability. MNI coordinates throughout the group exhibited a clear segregation according to the tested reading route; specific pseudo-word reading interferences were concentrated in a restricted inferior and anterior subpart of the left supramarginal gyrus (barycentre x = −68.1; y = −25.9; z = 30.2; Brodmann’s area 40) while specific word reading areas were located almost exclusively alongside the left superior temporal gyrus. Although half of the reading interferences found were nonspecific, the finding of specific lexical or sublexical interferences is new evidence that lexical and sublexical processes of reading could be partially supported by distinct cortical sub-regions despite their anatomical proximity. These data are in line with many brain activation studies that showed that left superior temporal and inferior parietal regions had a crucial role respectively in word and pseudoword reading and were core regions for dyslexia.     

Wording effects and the factor structure of the Hospital Anxiety & Depression Scale in HIV/AIDS patients on antiretroviral treatment in South Africa

Background

Given the immense burden of HIV/AIDS on health systems in sub-Saharan Africa and the intricate link between HIV/AIDS and mental health problems, health care providers need a valid and reliable instrument to assess mental health rapidly. The Hospital Anxiety and Depression Scale (HADS) may constitute such an instrument. The aims of this study were to: (1) examine the factor structure of the HADS in a population of South African HIV/AIDS patients on antiretroviral treatment (ART); and (2) identify and control the disturbing influence of systematic wording effects in vulnerable respondent groups.

Methodology/Principal Findings

The translated scale was administered to 716 HIV/AIDS patients enrolled in the public sector ART program in South Africa. A combined confirmatory factor analysis and correlated-traits-correlated-methods framework was used to determine the preferred factor structure of the HADS, while controlling for the disturbing influence of systematic wording effects. When assessing the structure without a negative wording factor, all three factor structures displayed an acceptable fit to the data. The three-factor solution best fitted the data. Addition of a method factor significantly improved the fit of all three factor solutions. Using χ² difference testing, Razavi''s one-factor solution displayed a superior fit compared to the other two factor solutions.

Conclusions

The study outcomes support the use of the HADS as a valid and reliable means to screen for mental health problems in HIV/AIDS patients enrolled in a public-sector ART program in a resource-limited context. The results demonstrate the importance of evaluating and correcting for wording effects when examining the factor structure of the screening instrument in vulnerable patient groups. In light of the inter-relationships between HIV/AIDS and mental health problems and the scarcity of adequate screening tools, additional studies on this topic are required.     

Dichroism of chlorophyll aI absorption change at 700 nm using chloroplastsoriented in a magnetic field.

Using spinach chloroplasts oriented in a magnetic field we have measured the dichroism of the photo-induced absorption change associated with chlorophyll a_I at 700 nm. The greatest absorption change was detected when the electric vector of the measuring beam was polarized parallel to the plane of the photosynthetic membranes. The large dichroic ratio (2.3 ± .1) measured at 700 nm indicates that the transition oscillator involved at this wavelength is nearly parallel to the plane of the photosynthetic membrane. This result is consistent with an earlier study by Junge and Eckhof.     

The normal modes of the gramicidin-A dimer channel.

The dynamics of the gramicidin-A dimer channel is studied in the harmonic approximation by a vibrational analysis of the atomic motions relative to their equilibrium positions. The system is represented by an empirical potential energy function, and all degrees of freedom (bonds lengths, bond angles, and torsional angles) are allowed to vary. The thermal fluctuations in the backbone dihedral angles phi and psi, atomic root mean square displacements, and the correlations between the different amide planes are computed. It is found that only adjacent dihedral psi i and phi i+1 are strongly correlated, while different hydrogen-bonded amide planes are only weakly correlated. Modes with relatively low vibrational frequencies (75-175 cm-1) make the dominant contributions to the carbonyl librations. The general flexibility of the structure and the role of carbonyl librations in the ion transport mechanism are discussed.     

Development of narrow immobilized pH gradients covering one pH unit for human seminal plasma proteomic analysis

Micropreparatively loaded two-dimensional (2-D) electrophoresis gels were used to identify human seminal plasma polypeptides by using narrow immobilized pH gradients (IPGs) covering one pH unit as first dimension. This investigation was restricted to IPG 4.5-5.5 and 5-6 because of the main spot distribution in the acidic part of the 2-D map performed with IPG 3-10, a zone presumed to be rich in spermatogenic markers. Both highly expressed and minor spots of the 2-D map were analyzed by matrix-assisted laser desorption/ionization mass spectrometry and tandem mass spectroscopy analysis. Identification was obtained by a combination of mass spectrometry and database searching. Identified proteins were of different origin from the male genital tract and some proteolysis was observed. They appeared as either isolated molecules or isoforms. At the analytical level, narrow IPGs allowed a two-fold increase in the number of spots, improved resolution of minor spots particularly in surrounding of highly expressed spots and sensitivity level. Some of these faint spots were differently expressed in azoospermic patients as compared to normospermic men. Therefore, zooming-in on the proteome of human seminal plasma allowed more accurate differential expression analysis of impaired spermatogenesis associated markers.