Two groups control light-induced schiff base deprotonation and the proton affinity of asp(85) in the Arg(82)His mutant of bacteriorhodopsin

Arg(82) is one of the four buried charged residues in the retinal binding pocket of bacteriorhodopsin (bR). Previous studies show that Arg(82) controls the pK(a)s of Asp(85) and the proton release group and is essential for fast light-induced proton release. To further investigate the role of Arg(82) in light-induced proton pumping, we replaced Arg(82) with histidine and studied the resulting pigment and its photochemical properties. The main pK(a) of the purple-to-blue transition (pK(a) of Asp(85)) is unusually low in R82H: 1.0 versus 2.6 in wild type (WT). At pH 3, the pigment is purple and shows light and dark adaptation, but almost no light-induced Schiff base deprotonation (formation of the M intermediate) is observed. As the pH is increased from 3 to 7 the M yield increases with pK(a) 4.5 to a value approximately 40% of that in the WT. A transition with a similar pK(a) is observed in the pH dependence of the rate constant of dark adaptation, k(da). These data can be explained, assuming that some group deprotonates with pK(a) 4.5, causing an increase in the pK(a) of Asp(85) and thus affecting k(da) and the yield of M. As the pH is increased from 7 to 10.5 there is a further 2.5-fold increase in the yield of M and a decrease in its rise time from 200 &mgr;s to 75 &mgr;s with pK(a) 9. 4. The chromophore absorption band undergoes a 4-nm red shift with a similar pK(a). We assume that at high pH, the proton release group deprotonates in the unphotolyzed pigment, causing a transformation of the pigment into a red-shifted "alkaline" form which has a faster rate of light-induced Schiff base deprotonation. The pH dependence of proton release shows that coupling between Asp(85) and the proton release group is weakened in R82H. The pK(a) of the proton release group in M is 7.2 (versus 5.8 in the WT). At pH < 7, most of the proton release occurs during O --> bR transition with tau approximately 45 ms. This transition is slowed in R82H, indicating that Arg(82) is important for the proton transfer from Asp(85) to the proton release group. A model describing the interaction of Asp(85) with two ionizable residues is proposed to describe the pH dependence of light-induced Schiff base deprotonation and proton release.     

Leaf architecture characters of <i>Vachellia tortilis</i> (Forssk.) Galasso and Banfi along longitudinal gradient in Limpopo Province,South Africa

This paper looked at the leaf architecture characteristics of Vachellia tortilis to determine if either there is or not an effect of the tropic line on plants. Vachellia tortilis leaves were sampled along a national road (N1) in Limpopo province. Sampling points were set 10 km apart away from the Tropic of Capricon in opposite directions. Leaf morphology revealed that leaves of V. tortilis are bipinnately compound with alternate arrangement. The venation pattern of the pinnules was eucamptodromus and brochidodromous with imperfect reticulation. Areoles were imperfect and pentagonal or irregular in shape.     

Effect of Eu doping on the thermoluminescence of UV and gamma irradiated Mg2B2O5 nanophosphors

This article presents the effect of europium (Eu) doping on the thermoluminescence (TL) of ultraviolet (UV-254 nm) and gamma irradiated triclinic Mg₂B₂O₅ nanophosphors. The diffuse reflectance predicts slight decrease in band gap from 5.18 to 4.99 eV with increasing Eu (1%, 3%, and 5%) content in Mg₂B₂O₅. The TL glow curves of UV irradiated samples comprised of a main peak around 500 K with weak intensity peak/shoulders in low temperature region. Interestingly Eu (3%) doped Mg₂B₂O₅ shows maximum TL intensity with suppression of low temperature shoulder peaks and almost linear UV dose dependent TL response. However, in the case of gamma irradiated Eu (1% and 3% doped) samples, TL glow curve comprises of a main peak around 425–445 K and closely lying peak around 500–515 K with relatively lesser intensity. In case of Eu (5%) doped samples, TL peak around 508 K starts dominating over peak around 425 K. TL of both UV and gamma irradiated samples showed the presence of various deep and shallow defect states within the bandgap of materials having different kinetic parameters, which were determined using TLanal software based on Kiti's general order equation. The present study shows that Eu doped Mg₂B₂O₅ nanophosphors can be tuned for UV and gamma dosimetry.     

Rice A20/AN1 zinc-finger containing stress-associated proteins (SAP1/11) and a receptor-like cytoplasmic kinase (OsRLCK253) interact via A20 zinc-finger and confer abiotic stress tolerance in transgenic Arabidopsis plants

? The inbuilt mechanisms of plant survival have been exploited for improving tolerance to abiotic stresses. Stress-associated proteins (SAPs), containing A20/AN1 zinc-finger domains, confer abiotic stress tolerance in different plants, however, their interacting partners and downstream targets remain to be identified. ? In this study, we have investigated the subcellular interactions of rice SAPs and their interacting partner using yeast two-hybrid and fluorescence resonance energy transfer (FRET) approaches. Their efficacy in improving abiotic stress tolerance was analysed in transgenic Arabidopsis plants. Regulation of gene expression by genome-wide microarray in transgenics was used to identify downstream targets. ? It was found that the A20 domain mediates the interaction of OsSAP1 with self, its close homolog OsSAP11 and a rice receptor-like cytoplasmic kinase, OsRLCK253. Such interactions between OsSAP1/11 and with OsRLCK253 occur at nuclear membrane, plasma membrane and in nucleus. Functionally, both OsSAP11 and OsRLCK253 could improve the water-deficit and salt stress tolerance in transgenic Arabidopsis plants via a signaling pathway affecting the expression of several common endogenous genes. ? Components of a novel stress-responsive pathway have been identified. Their stress-inducible expression provided the protection against yield loss in transgenic plants, indicating the agronomic relevance of OsSAP11 and OsRLCK253 in conferring abiotic stress tolerance.     

Can correcting the ΔF508-CFTR proteostasis-defect rescue CF lung disease?

Protein homeostasis (proteostasis) generates and maintains individual proteins in their folded and functional-competent states. The components of the cellular proteostasis machinery also dictate the functional lifetime of a protein by constantly regulating its conformation, concentration and subcellular location. The autosomal recessive disease cystic fibrosis (CF) is caused by a proteostasis-defect in CF transmembrane conductance regulator (CFTR). The most common CF mutation leading to this proteostasis-defect is the deletion of a phenylalanine residue at position 508 (ΔF508) of the CFTR protein. This ΔF508-CFTR protein is prone to aberrant folding, increased ER-associated degradation, atypical intracellular trafficking and reduced stability at the apical membrane. This ΔF508-CF proteostasis-defect leads to an obstructive lung disease characterized by impaired ion transport in airway epithelial cells, mucus buildup in air space and chronic airway inflammation. We assess here whether correcting the underlying defect in ΔF508-CFTR protein processing using therapeutic proteostasis regulators can treat chronic CF lung disease. As a proof of concept, recent studies support that the selective modulation of mutant-CFTR proteostasis may offer promising therapies to reverse chronic CF lung disease.