Why do microorganisms have aquaporins?

Aquaporins are channel proteins that enhance the permeability of cell membranes for water. They have been found in Bacteria, Archaea and Eukaryotes. However, their absence in many microorganisms suggests that aquaporins do not fulfill a broad role such as turgor regulation or osmoadaptation but, instead, fulfill a role that enables microorganisms to have specific lifestyles. The recent discovery that aquaporins enhance cellular tolerance against rapid freezing suggests that they have ecological relevance. We have identified several examples of large-scale freeze-thawing of microbes in nature and we also draw attention to alternative lifestyle-related functions for aquaporins, which will be a focus of future research.     

Methyl substituents at the 11 or 12 position of retinal profoundly and differentially affect photochemistry and signalling activity of rhodopsin

The C-11=C-12 double bond of the retinylidene chromophore of rhodopsin holds a central position in its light-induced photoisomerization and hence the photosensory function of this visual pigment. To probe the local environment of the HC-11=C-12H element we have prepared the 11-methyl and 12-methyl derivatives of 11-Z retinal and incorporated these into opsin to generate the rhodopsin analogs 11-methyl and 12-methyl rhodopsin. These analog pigments form with much slower kinetics and lower efficiency than the native pigment. The initial photochemistry and the signaling activity of the analog pigments were investigated by UV-vis and FTIR spectroscopy, and by a G protein activation assay. Our data indicate that the ultrafast formation of the first photointermediate is strongly perturbed by the presence of an 11-methyl substituent, but much less by a 12-methyl substituent. These results support the current concept of the mechanism of the primary photoisomerization event in rhodopsin. An important stronghold of this concept is an out-of-plane movement of the C-12H element, which is facilitated by torsion as well as extended positive charge delocalization into the C-10-C-13 segment of the chromophore. We argue that this mechanism is maintained principally with a methyl substituent at C-12. In addition, we show that both an 11-methyl and a 12-methyl substitutent perturb the photointermediate cascade and finally yield a low-activity state of the receptor. The 11-methyl pigment retains about 30% of the G protein activation rate of native rhodopsin, while the 12-methyl chromophore behaves like an inverse agonist up to at least 20 degrees C, trapping the protein in a perturbed Meta-I-like conformation. We conclude that the isomerization region of the chromophore and the spatial structure of the binding site are finely tuned, in order to achieve a high photosensory potential with an efficient pathway to a high-activity state.     

Structural role for Tyr-104 in Escherichia coli isopentenyl-diphosphate isomerase: site-directed mutagenesis, enzymology, and protein crystallography

Isopentenyl-diphosphate (IPP):dimethylallyl diphosphate isomerase is a key enzyme in the biosynthesis of isoprenoids. The mechanism of the isomerization reaction involves protonation of the unactivated carbon-carbon double bond in the substrate, but identity of the acidic moiety providing the proton is still not clear. Multiple sequence alignments and geometrical features observed in crystal structures of complexes with IPP isomerase suggest that Tyr-104 could play an important role during catalysis. A series of mutants was constructed by directed mutagenesis and characterized by enzymology. Crystallographic and thermal denaturation data for Y104A and Y104F mutants were obtained. Those data demonstrate the importance of residue Tyr-104 for proper folding of Escherichia coli type I IPP isomerase.     

Endothelial Progenitor Cells and Cardiovascular Events in Patients with Chronic Kidney Disease – a Prospective Follow-Up Study

Background

Endothelial progenitor cells (EPCs) mediate vascular repair and regeneration. Their number in peripheral blood is related to cardiovascular events in individuals with normal renal function.

Methods

We evaluated the association between functionally active EPCs (cell culture) and traditional cardiovascular risk factors in 265 patients with chronic kidney disease stage V receiving hemodialysis therapy. Thereafter, we prospectively assessed cardiovascular events, e.g. myocardial infarction, percutaneous transluminal coronary angioplasty (including stenting), aorto-coronary bypass, stroke and angiographically verified stenosis of peripheral arteries, and cardiovascular death in this cohort.

Results

In our patients EPCs were related only to age (r = 0.154; p = 0.01). During a median follow-up period of 36 months 109 (41%) patients experienced a cardiovascular event. In a multiple Cox regression analysis, we identified EPCs (p = 0.03) and patient age (p = 0.01) as the only independent variables associated with incident cardiovascular events. Moreover, a total of 70 patients died during follow-up, 45 of those due to cardiovascular causes. Log rank test confirmed statistical significance for EPCs concerning incident cardiovascular events (p = 0.02).

Conclusions

We found a significant association between the number of functionally active EPCs and cardiovascular events in patients with chronic kidney disease. Thus, defective vascular repair and regeneration may be responsible, at least in part, for the enormous cardiovascular morbidity in this population.     

Impaired attribution of emotion to facial expressions in anxiety and major depression

Background

Recognition of others'' emotions is an important aspect of interpersonal communication. In major depression, a significant emotion recognition impairment has been reported. It remains unclear whether the ability to recognize emotion from facial expressions is also impaired in anxiety disorders. There is a need to review and integrate the published literature on emotional expression recognition in anxiety disorders and major depression.

Methodology/Principal Findings

A detailed literature search was used to identify studies on explicit emotion recognition in patients with anxiety disorders and major depression compared to healthy participants. Eighteen studies provided sufficient information to be included. The differences on emotion recognition impairment between patients and controls (Cohen''s d) with corresponding confidence intervals were computed for each study. Over all studies, adults with anxiety disorders had a significant impairment in emotion recognition (d = −0.35). In children with anxiety disorders no significant impairment of emotion recognition was found (d = −0.03). Major depression was associated with an even larger impairment in recognition of facial expressions of emotion (d = −0.58).

Conclusions/Significance

Results from the current analysis support the hypothesis that adults with anxiety disorders or major depression both have a deficit in recognizing facial expression of emotions, and that this deficit is more pronounced in major depression than in anxiety.     

Antioxidants protect keratinocytes against M. ulcerans mycolactone cytotoxicity

Background

Mycobacterium ulcerans is the causative agent of necrotizing skin ulcerations in distinctive geographical areas. M. ulcerans produces a macrolide toxin, mycolactone, which has been identified as an important virulence factor in ulcer formation. Mycolactone is cytotoxic to fibroblasts and adipocytes in vitro and has modulating activity on immune cell functions. The effect of mycolactone on keratinocytes has not been reported previously and the mechanism of mycolactone toxicity is presently unknown. Many other macrolide substances have cytotoxic and immunosuppressive activities and mediate some of their effects via production of reactive oxygen species (ROS). We have studied the effect of mycolactone in vitro on human keratinocytes—key cells in wound healing—and tested the hypothesis that the cytotoxic effect of mycolactone is mediated by ROS.

Methodology/Principal Findings

The effect of mycolactone on primary skin keratinocyte growth and cell numbers was investigated in serum free growth medium in the presence of different antioxidants. A concentration and time dependent reduction in keratinocyte cell numbers was observed after exposure to mycolactone. Several different antioxidants inhibited this effect partly. The ROS inhibiting substance deferoxamine, which acts via chelation of Fe²⁺, completely prevented mycolactone mediated cytotoxicity.

Conclusions/Significance

This study demonstrates that mycolactone mediated cytotoxicity can be inhibited by deferoxamine, suggesting a role of iron and ROS in mycolactone induced cytotoxicity of keratinocytes. The data provide a basis for the understanding of Buruli ulcer pathology and the development of improved therapies for this disease.     

RhoA regulates peroxisome association to microtubules and the actin cytoskeleton

The current view of peroxisome inheritance provides for the formation of new peroxisomes by both budding from the endoplasmic reticulum and autonomous division. Here we investigate peroxisome-cytoskeleton interactions and show by proteomics, biochemical and immunofluorescence analyses that actin, non-muscle myosin IIA (NMM IIA), RhoA, Rho kinase II (ROCKII) and Rab8 associate with peroxisomes. Our data provide evidence that (i) RhoA in its inactive state, maintained for example by C. botulinum toxin exoenzyme C3, dissociates from peroxisomes enabling microtubule-based peroxisomal movements and (ii) dominant-active RhoA targets to peroxisomes, uncouples the organelles from microtubules and favors Rho kinase recruitment to peroxisomes. We suggest that ROCKII activates NMM IIA mediating local peroxisomal constrictions. Although our understanding of peroxisome-cytoskeleton interactions is still incomplete, a picture is emerging demonstrating alternate RhoA-dependent association of peroxisomes to the microtubular and actin cytoskeleton. Whereas association of peroxisomes to microtubules clearly serves bidirectional, long-range saltatory movements, peroxisome-acto-myosin interactions may support biogenetic functions balancing peroxisome size, shape, number, and clustering.