Plasmodium berghei (ANKA): infection induces CYP2A5 and 2E1 while depressing other CYP isoforms in the mouse liver

It has been reported that malaria infection impairs hepatic drug clearance and causes a down-regulation of CYP-mediated monooxygenase activities in rodents and humans. In the present study, we investigated the effects of Plasmodium berghei infection on the activity of liver monooxygenases in female DBA/2 and C57BL/6 mice. In both mouse strains, P. berghei infection decreased activities mediated by CYP1A (EROD: DBA/2 65.3%, C57BL/6 44.7%) and 2B (BROD: DBA/2 64.3%, C57BL/6 49.8%) subfamily isoforms and increased activities mediated by 2A5 (COH: DBA/2 182.4%, C57BL/6 148.5%) and 2E1 (PNPH: DBA/2 177.8%, C57BL/6 128.5%) isoforms as compared to non-infected controls. Since malaria infection also produced an increase in ALT (273.1%) and AST (354.1%) activities in the blood serum, our findings are consistent with the view that CYP2A5 activity is induced by liver injury. An almost generalized depression of CYP-mediated activities has been found with numerous infections and inflammatory stimuli but an induction of CYP2A5 had been previously noted only in some viral hepatitis and trematode (liver fluke) infections.     

Ubiquinone (coenzyme Q10) binding sites: low dielectric constant of the gate prevents the escape of the semiquinone

The photosynthetic reaction center (RC) from purple bacteria is frequently used as a model for the interaction of ubiquinones (coenzyme Q) with membrane proteins. Single-turnover flash activation of RC leads to formation of the semiquinone (SQ) of the secondary acceptor quinone after odd flashes and quinol after even flashes. The ubiquinol escapes the binding site in 1 ms, while the SQ does not leave the binding site for at least 5 min. Observed difference between these times suggests a large energetic barrier for the SQ. However, high apparent dielectric constant in the vicinity of the quinone ring (>or=25) results in a relatively small electrostatic energy of SQ stabilization. To resolve this apparent contradiction I suggest that a significant part of the kinetic stabilization of the SQ is achieved by the special topology of the binding site in which quinone can exit the binding site only by moving its headgroup toward the center of the membrane. The large energetic penalty of transferring the charged headgroup to the membrane dielectric can explain the observed kinetic stability of the SQ.     

Atomic determinants of state-dependent block of sodium channels by charged local anesthetics and benzocaine

Molecular modeling predicts that a local anesthetic (LA) lidocaine binds to the resting and open Na(v)1.5 in different modes, interacting with LA-sensing residues known from experiments. Besides the major pathway via the open activation gate, LAs can reach the inner pore via a "sidewalk" between D3S6, D4S6, and D3P. The ammonium group of a cationic LA binds in the focus of the pore-helices macrodipoles, which also stabilize a Na(+) ion chelated by two benzocaine molecules. The LA's cationic group and a Na(+) ion in the selectivity filter repel each other suggesting that the Na(+) depletion upon slow inactivation would stabilize a LA, while a LA would stabilize slow-inactivated states.     

Interaction of nucleoredoxin with protein phosphatase 2A

A trimeric protein phosphatase 2A (PP2A(T55)) composed of the catalytic (PP2Ac), structural (PR65/A), and regulatory (PR55/B) subunits was isolated from rabbit skeletal muscle by thiophosphorylase affinity chromatography, and contained two additional proteins of 54 and 55 kDa, respectively. The 54 kDa protein was identified as eukaryotic translation termination factor 1 (eRF1) and as a PP2A interacting protein. The 55 kDa protein is now identified as nucleoredoxin (NRX). The formation of a complex between GST-NRX, PP2A(C) and PP2A(D) was demonstrated by pull-down experiments with purified forms of PP2A, and by immunoprecipitation of HA-tagged NRX expressed in HEK293 cells complexed endogenous PP2A subunits. Analysis of PP2A activity in the presence of GST-NRX showed that NRX competed with polycations for both stimulatory and inhibitory effects on different forms of PP2A.     

Erythropoietin activates caspase-3 and downregulates CAD during erythroid differentiation in TF-1 cells - a protection mechanism against DNA fragmentation

The involvement of caspase-3 and its failure in the induction of DNA fragmentation during erythropoiesis were investigated with TF-1 cells. During erythroid differentiation, caspase-3 activation and cleavage of caspase-3 substrates such as ICAD (inhibitor of caspase-activated DNase) were detected without concomitant phosphatidyl-serine (PS) externalization and DNA fragmentation. These observations are in contrast to our understanding that DNA is degraded by CAD (caspase-activated DNase) when ICAD is cleaved by caspase-3. Our study demonstrates that CAD is downregulated at the mRNA and protein level during the erythroid differentiation in TF-1 cells. This provides a mechanism for the first time how cells avoid DNA fragmentation with activated caspase-3.     

Role of the leader sequence in tobacco pectin methylesterase secretion

We report that unprocessed tobacco pectin methylesterase (PME) contains N-terminal pro-sequence including the transmembrane (TM) domain and spacer segment preceding the mature PME. The mature portion of PME was replaced by green fluorescent protein (GFP) gene and various deletion mutants of pro-sequence fused to GFP were cloned into binary vectors and agroinjected in Nicotiana benthamiana leaves. The PME pro-sequence delivered GFP to the cell wall (CW). We showed that a transient binding of PME TM domain to endoplasmic reticulum membranes occurs upon its transport to CW. The CW targeting was abolished by various deletions in the TM domain, i.e., anchor domain was essential for secretion of GFP to CW. By contrast, even entire deletion of the spacer segment had no influence on GFP targeting.     

Biophysical re-equilibration of Ca2+ fluxes as a simple biologically plausible explanation for complex intracellular Ca2+ release patterns

Physiological regulation of Ca(2+) release from the endoplasmic reticulum (ER) is critical for cell function. Recent direct measurements of free [Ca(2+)] inside the ER ([Ca(2+)](ER)) revealed that [Ca(2+)](ER) itself is a key regulator of ER Ca(2+) handling. However, the role of this new regulatory process in generating various patterns of Ca(2+) release remains to be elucidated in detail. Here, we incorporate the recently quantified experimental correlations between [Ca(2+)](ER) and Ca(2+) movements across the ER membrane into a mathematical model ER Ca(2+) handling. The model reproduces basic experimental dynamics of [Ca(2+)](ER). Although this was not goal in model design, the model also exhibits mechanistically unclear experimental phenomena such as "quantal" Ca(2+) release, and "store charging" by increasing resting cytosolic [Ca(2+)]. While more complex explanations cannot be ruled out, on the basis of our data we propose that "quantal release" and "store charging" could be simple re-equilibration phenomena, predicted by the recently quantified biophysical dynamics of Ca(2+) movements across the ER membrane.     

Stimulation of arachidonic acid release by vasopressin in A7r5 vascular smooth muscle cells mediated by Ca2+-stimulated phospholipase A2

Arachidonic acid (AA) regulates many aspects of vascular smooth muscle behaviour, but the mechanisms linking receptors to AA release are unclear. In A7r5 vascular smooth muscle cells pre-labelled with (3)H-AA, vasopressin caused a concentration-dependent stimulation of 3H-AA release that required phospholipase C and an increase in cytosolic [Ca2+]. Ca2+ release from intracellular stores and Ca2+ entry via L-type channels or the capacitative Ca2+ entry pathway were each effective to varying degrees. Selective inhibitors of PLA2 inhibited the 3H-AA release evoked by vasopressin, though not the underlying Ca2+ signals, and established that cPLA2 mediates the release of AA. We conclude that in A7r5 cells vasopressin stimulates AA release via a Ca2+-dependent activation of cPLA2.     

PsbS enhances nonphotochemical fluorescence quenching in the absence of zeaxanthin

Leaves and chloroplasts from Arabidopsis plants with increased amounts of PsbS protein showed the same percentage increase in nonphotochemical quenching in comparison to the wild type both in the presence and absence of zeaxanthin. The absorption change at 525-535 nm was also more pronounced in both cases. It is suggested that PsbS alone can cause the quenching, supporting the model in which zeaxanthin acts as an allosteric activator and is not the primary cause of the process. It is proposed that PsbS acts as a trigger of the conformational change that leads to the establishment of nonphotochemical quenching.