Characterization of Vitronectin-Binding Proteins of Staphylococcus epidermidis

Staphylococcus epidermidis is the most common microorganism that is isolated from the cerebrospinal fluid (CSF) shunt infection patients. Vitronectin adsorbed on the surface of implants may mediate bacterial adhesion and colonization. To characterize vitronectin-binding properties, we analyzed S. epidermidis BD5703 isolated from a CSF shunt infection. Expression of vitronectin-binding protein(s) depended on culture media. Two proteins (60 and 52 kDa) were purified from vitronectin affinity chromatography. Two other vitronectin-binding proteins (21 and 16 kDa) were purified from an ion-exchange column. All purified proteins blocked bacterial binding of immobilized vitronectin significantly except the 16-kDa protein. The N-terminal sequences of the 21- and 16-kDa proteins did not show any appreciable amino acid sequence homology. The 52-kDa protein was sequenced by mass spectrometry and identified as an autolysin. This report demonstrates that interaction of vitronectin with multiple recognition sites on BD5703 surface may contribute to bacterial colonization. Received: 6 September 2000 / Accepted: 6 November 2000     

Oxidative modification and inactivation of the proteasome during coronary occlusion/reperfusion

Restoration of blood flow to ischemic myocardial tissue results in an increase in the production of oxygen radicals. Highly reactive, free radical species have the potential to damage cellular components. Clearly, maintenance of cellular viability is dependent, in part, on the removal of altered protein. The proteasome is a major intracellular proteolytic system which degrades oxidized and ubiquitinated forms of protein. Utilizing an in vivo rat model, we demonstrate that coronary occlusion/reperfusion resulted in declines in chymotrypsin-like, peptidylglutamyl-peptide hydrolase, and trypsin-like activities of the proteasome as assayed in cytosolic extracts. Analysis of purified 20 S proteasome revealed that declines in peptidase activities were accompanied by oxidative modification of the protein. We provide conclusive evidence that, upon coronary occlusion/reperfusion, the lipid peroxidation product 4-hydroxy-2-nonenal selectively modifies 20 S proteasome alpha-like subunits iota, C3, and an isoform of XAPC7. Occlusion/reperfusion-induced declines in trypsin-like activity were largely preserved upon proteasome purification. In contrast, loss in chymotrypsin-like and peptidylglutamyl-peptide hydrolase activities observed in cytosolic extracts were not evident upon purification. Thus, decreases in proteasome activity are likely due to both direct oxidative modification of the enzyme and inhibition of fluorogenic peptide hydrolysis by endogenous cytosolic inhibitory protein(s) and/or substrate(s). Along with inhibition of the proteasome, increases in cytosolic levels of oxidized and ubiquitinated protein(s) were observed. Taken together, our findings provide insight into potential mechanisms of coronary occlusion/reperfusion-induced proteasome inactivation and cellular consequences of these events.     

Size of environmental grain and resource matching

For most animals their foraging environment consists of a patch network. In random environments there are no spatial autocorrelation at all, while in fine-grained systems positive autocorrelations flip to negative ones and back again against distance. With increasing grain size the turnover rate of spatial autocorrelation slows down. Using a cellular automaton with foragers having limited information about their feeding environment we examined how well consumer numbers matched resource availability, also known as the ideal free distribution. The match is the better the smaller the size of the environmental grain. This is somewhat contrary to the observation that in large-grained environments the spatial autocorrelation is high and positive over long distances. In such an environment foragers, by knowing a limited surrounding, should in fact know a much larger area because of the spatially autocorrelated resource pattern. Yet, when foragers have limited knowledge, we observed that the degree of undermatching (i.e., more individuals in less productive patches than expected) increases with increasing grain size.     

Mobile Link Organisms and Ecosystem Functioning: Implications for Ecosystem Resilience and Management

Current natural resource management seldom takes the ecosystem functions performed by organisms that move between systems into consideration. Organisms that actively move in the landscape and connect habitats in space and time are here termed “mobile links.” They are essential components in the dynamics of ecosystem development and ecosystem resilience (that is, buffer capacity and opportunity for reorganization) that provide ecological memory (that is, sources for reorganization after disturbance). We investigated the effects of such mobile links on ecosystem functions in aquatic as well as terrestrial environments. We identify three main functional categories: resource, genetic, and process linkers and suggest that the diversity within functional groups of mobile links is a central component of ecosystem resilience. As the planet becomes increasingly dominated by humans, the magnitude, frequency, timing, spatial extent, rate, and quality of such organism-mediated linkages are being altered. We argue that global environmental change can lead to (a) the decline of essential links in functional groups providing pollination, seed dispersal, and pest control; (b) the linking of previously disconnected areas, for example, the spread of vector-borne diseases and invasive species; and (c) the potential for existing links to become carriers of toxic substances, such as persistent organic compounds. We conclude that knowledge of interspatial exchange via mobile links needs to be incorporated into management and policy-making decisions in order to maintain ecosystem resilience and hence secure the capacity of ecosystems to supply the goods and services essential to society. Received 23 April 2001; accepted 17 June 2002.     

Respiratory depression by GABA-ergic drugs in the preterm rabbit

Respiratory parameters were studied in preterm rabbits (gestational age 29 days) after intraperitoneal administration of the GABA-like drugs gamma-hydroxybutyric acid and muscimol. The animals were anaesthetized with 0.7% halothane in oxygen and studied in a closed body plethysmograph. Both drugs induced a decreased respiratory frequency and minute volume. Tidal volume decreased after muscimol, but not after gamma-hydroxybutyric acid administration. The present results indicate that an increased GABA-ergic activity causes respiratory depression in the preterm neonatal rabbit, presumably by an action on central nervous frequency and tidal volume modulating systems. Central GABA neurons may thus be involved in the pathogenesis of neonatal respiratory depression and irregular breathing.     

Increased Concentrations of Glutamate and Glutamine in Normal-Appearing White Matter of Patients with Multiple Sclerosis and Normal MR Imaging Brain Scans

In Multiple Sclerosis (MS) the relationship between disease process in normal-appearing white matter (NAWM) and the development of white matter lesions is not well understood. In this study we used single voxel proton ‘Quantitative Magnetic Resonance Spectroscopy’ (qMRS) to characterize the NAWM and thalamus both in atypical ‘Clinically Definite MS’ (CDMS) patients, MRI_neg (N = 15) with very few lesions (two or fewer lesions), and in typical CDMS patients, MRI_pos (N = 20) with lesions, in comparison with healthy control subjects (N = 20). In addition, the metabolite concentrations were also correlated with extent of brain atrophy measured using Brain Parenchymal Fraction (BPF) and severity of the disease measured using ‘Multiple Sclerosis Severity Score’ (MSSS). Elevated concentrations of glutamate and glutamine (Glx) were observed in both MS groups (MRI_neg 8.12 mM, p<0.001 and MRI_pos 7.96 mM p<0.001) compared to controls, 6.76 mM. Linear regressions of Glx and total creatine (tCr) with MSSS were 0.16±0.06 mM/MSSS (p = 0.02) for Glx and 0.06±0.03 mM/MSSS (p = 0.04) for tCr, respectively. Moreover, linear regressions of tCr and myo-Inositol (mIns) with BPF were −6.22±1.63 mM/BPF (p<0.001) for tCr and −7.71±2.43 mM/BPF (p = 0.003) for mIns. Furthermore, the MRI_pos patients had lower N-acetylaspartate and N-acetylaspartate-glutamate (tNA) and elevated mIns concentrations in NAWM compared to both controls (tNA: p = 0.04 mIns p<0.001) and MRI_neg (tNA: p = 0.03 , mIns: p = 0.002). The results suggest that Glx may be an important marker for pathology in non-lesional white matter in MS. Moreover, Glx is related to the severity of MS independent of number of lesions in the patient. In contrast, increased glial density indicated by increased mIns and decreased neuronal density indicated by the decreased tNA, were only observed in NAWM of typical CDMS patients with white matter lesions.     

Expression of spinach plastocyanin in E. coli

An expression vector designed for overexpression of plastocyanin in the periplasmic space of E. coli has been developed. The vector contains the signal peptide sequence of Pseudomonas aeruginosa azurin and the mature sequence of spinach plastocyanin. The precursor is efficiently translocated to the periplasmic space and correctly processed to mature plastocyanin. No detectable amount of plastocyanin was present in the cytoplasmic or in the membrane fraction. A large scale preparation of the recombinant plastocyanin in a 20 litre fermentor yielded approximately 30 mg of pure plastocyanin. The recombinant protein obtained from E. coli shows CD, EPR and optical properties identical to plastocyanin isolated from spinach.