Visualizing Arp2/3 complex activation mediated by binding of ATP and WASp using structural mass spectrometry

Actin-related protein (Arp) 2/3 complex nucleates new branches in actin filaments playing a key role in controlling eukaryotic cell motility. This process is tightly regulated by activating factors: ATP and WASp-family proteins. However, the mechanism of activation remains largely hypothetical. We used radiolytic protein footprinting with mass spectrometry in solution to probe the effects of nucleotide- and WASp-binding on Arp2/3. These results represent two significant advances in such footprinting approaches. First, Arp2/3 is the most complex macromolecular assembly yet examined; second, only a few picomoles of Arp2/3 was required for individual experiments. In terms of structural biology of Arp 2/3, we find that ATP binding induces conformational changes within Arp2/3 complex in Arp3 (localized in peptide segments 5-18, 212-225, and 318-327) and Arp2 (within peptide segment 300-316). These data are consistent with nucleotide docking within the nucleotide clefts of the actin-related proteins promoting closure of the cleft of the Arp3 subunit. However, ATP binding does not induce conformational changes in the other Arp subunits. Arp2/3 complex binds to WASp within the C subdomain at residue Met 474 and within the A subdomain to Trp 500. Our data suggest a bivalent attachment of WASp to Arp3 (within peptides 162-191 and 318-329) and Arp2 (within peptides 66-80 and 87-97). WASp-dependent protections from oxidation within peptides 54-65 and 80-91 of Arp3 and in peptides 300-316 of Arp2 suggest domain rearrangements of Arp2 and Arp3 resulting in a closed conformational state consistent with an "actin-dimer" model for the active state.     

The Relationship of Maternal HIV Status and Home Variables to Academic Performance of African American Children

The incidence of HIV/AIDS continues to rise among impoverished, urban, African American women, yet the children of these women have been overlooked in the literature. The primary aim of this study was to determine the relationship of maternal HIV status to child academic performance. In addition, we examined whether family variables (e.g., maternal education, parenting) related to academic performance similarly or differently in families in which mothers were and were not infected. Finally, the roles of stage of maternal HIV infection and school attendance in the relation between maternal HIV status and child academic performance were examined. Participants included two groups: 85 African American, HIV-infected women and their noninfected children, and 148 noninfected African American women and their children. Maternal HIV status predicted children's grades, and the relation between family variables and child academic performance was similar in the infected and noninfected samples. School attendance appeared to be a mechanism that may explain the relationship between maternal HIV status and child academic performance.     

Catheter-associated UTIs in patients after major gynaecological surgery

A group of nurses undertook an audit across two hospitals comparing the incidence of catheter-related urinary tract infections in patients who had catheters inserted during major gynaecological surgery. The data suggests that using an anaesthetic lubricating gel for catheterisation reduces urinary tract infection rates for these patients.     

The promiscuous nature of the cardiac sodium current

Voltage-gated sodium channels (Na(V)s) are essential in propagating neuronal electrical impulse and triggering muscle contraction. In the heart, the Na(+) channel isoform Na(V)1.5 is strongly expressed and in the past was thought to be solely responsible for generating the cardiac Na(+) current (I(Na)). Recent studies, however, revealed that neuronal and skeletal muscle Na(+) channel isoforms are also expressed in the heart and contribute to cardiac I(Na). Amongst the findings is that many neuronal type Na(V)s are expressed in specific areas of the conduction system and ventricles. The contribution of these TTX-sensitive channels to normal cardiac function remains unclear but these data raise the possibility of a more prominent role of TTX-sensitive channels in conduction. Moreover, cardiac arrhythmias are commonly observed in many neuronal and musculoskeletal diseases despite their exclusive linkage to mutations in the neuronal and skeletal muscle sodium channel isoforms. The cause for these arrhythmias remains poorly understood. These recent findings indicate that neuronal and skeletal muscle sodium channels are expressed in areas of the heart that may be involved in the clinical phenotypes observed. The purpose of this review is to give an overview of the evidence for the presence of TTX-sensitive Na(V) isoforms in the heart and present the hypothesis brought forward so far for their direct role in cardiac function. These data demonstrate the promiscuous nature of the cardiac sodium current at the molecular level and should help us to bridge the gap that exists between our understanding of cardiac physiology and arrhythmias associated to brain and myotonic diseases.     

Multiparametric evaluation of brain functions in the Mongolian gerbil in vivo.

We have developed the multiprobe assembly (MPA) by which metabolic, ionic and electrical activities can be monitored from the surface of the brain. In the present study we included optical fibers for the monitoring of intracapillary hemoglobin oxygenation by use of the Erlangen Microlight Guide Spectrophotometer (EMPHO-I) from the surface of the gerbil brain. The newly developed MPA provides simultaneous information about oxygen delivery (oxydeoxy Hb), tissue pO2 level, as well as the intracellular oxygen balance (intramitochondrial redox state). The ionic homeostasis was evaluated by monitoring extracellular K+ and Ca2+ activities reflecting the permeability changes of cation channels as well as the activities of Na+,K(+)-ATPase and other ion linked transport processes. The electrical activities were monitored by a bipolar electrocortical surface probe and DC steady potential. The subjects of the present study were Mongolian gerbils (Meriones unguiculatus) anesthetized and operated according to our routine techniques. After 30 min of recovery from the operation each gerbil was exposed to a short anoxia, graded hypoxia, ischemia as well as spreading depression. The results can be summarized as follows: 1. A clear correlation was recorded between the changes in oxydeoxy Hb spectra, tissue pO2 level and oxidation-reduction state of intramitochondrial NADH under oxygen deficiency situations (hypoxia, ischemia). 2. Blood volume changes under various perturbations monitored by various probes (366 reflectance and EMPHO-I) correlated very well with each other. 3. The degree of inhibition of Na+,K(+)-ATPase induced by oxygen deficiency could be interpreted by changes in extracellular levels of K+ measured by the surface mini-electrode. 4. Brain stimulation induced by spreading depression mechanism led to transient changes in ionic homeostasis and increase in energy requirements. The major HbO2 response was an increase in oxygenation due to the large CBF increase as monitored by the laser Doppler flowmeter. 5. Changes in oxy-deoxy Hb under fast scanning of 500-600 nm during 2-3 seconds of bilateral carotid arterial occlusion provided an indirect index for tissue O2 consumption.     

Depolarization-induced changes in cellular energy production.

Addition of high concentrations of KC1 to preparations of rat brain synaptosomes incubated with either glucose or pyruvate caused a transient stimulation of oxygen uptake. This increased respiration was insensitive to 1 mM ouabain and 10 microM ruthenium red but was dependent upon the presence of calcium. With 40 mM KCl in the incubation medium, the levels of high-energy phosphate compounds in the synaptosomes were unaltered, whereas pyridine nucleotides underwent a rapid, albeit small and temporary, oxidation. It is postulated that there is a calcium-dependent mechanism in synaptosomes through which the function of the mitochondrial respiratory chain or of oxidative phosphorylation is stimulated directly without the involvement of either adenine nucleotides or mitochondrial dehydrogenases.     

Three-Dimensional metabolic mapping of the freeze-trapped brain: Effects of ischemia in the mongolian gerbil

The effects of unilateral carotid artery (left or right) occlusion on the three-dimensional metabolic mapping were studied in the Mongolian gerbil (Meriones unguiculatus). The brain was freeze-trapped by the liquid nitrogen funnel technique and was analyzed for the two-dimensional distribution of the reduced pyridine nucleotides and oxidized flavoprotein using a time-sharing micro-light guide surface fluorometer/reflectometer. The results could be summarized as follows. Bilateral carotid artery occlusion induced uniform effects in terms of redox state in the cerebral cortex and the olfactory bulbs. After unilateral carotid occlusion, the redox state of the ischemic ipsilateral hemisphere was higher and was not affected by blood volume changes as evaluated from the reflectance signal scanned in several brains. The narrow band of tissue near the midline of the ischemic hemisphere connected to the contralateral hemisphere blood supply appeared in a large number of gerbils. The anomaly in the redox state of the intracellular space also appeared in subcortical structures, as seen in all the two-dimensional mappings measured. It seems that blood circulation to the two olfactory bulbs is connected to the same blood vessel. It is suggested that unilateral carotid artery-occluded gerbils may show large variability inside the same hemisphere and therefore results must be evaluated very carefully.