High variety of different simian T-cell leukemia virus type 1 strains in chimpanzees (Pan troglodytes verus) of the Taï National Park, Côte d'Ivoire

We found human T-cell leukemia virus type 1- and simian T-cell leukemia virus type 1 (STLV-1)-related infections in 5 of 10 chimpanzees originating from three groups of wild chimpanzees. The new virus isolates showed a surprising heterogeneity not only in comparison to STLV-1 described previously in other primate species but also between the different chimpanzee groups, within a group, or even between strains isolated from an individual animal. The interdisciplinary combination of virology, molecular epidemiology, and long-term behavioral studies suggests that the primary route of infection might be interspecies transmission from other primates, such as red colobus monkeys, that are hunted and consumed by chimpanzees.     

Allosteric models for multimeric proteins: oxygen-linked effector binding in hemocyanin

In many crustaceans, changing concentrations of several low molecular weight compounds modulates hemocyanin oxygen binding, resulting in lower or higher oxygen affinities of the pigment. The nonphysiological effector caffeine and the physiological modulator urate, the latter accumulating in the hemolymph of the lobster Homarus vulgaris during hypoxia, increase hemocyanin oxygen affinity and decrease cooperativity of oxygen binding. To derive a model that describes the mechanism of allosteric interaction between hemocyanin and oxygen in the presence of urate or caffeine, studies of oxygen, urate, and caffeine binding to hemocyanin were performed. Exposure of lobster hemocyanin to various pH values between 7.25 and 8.15 resulted in a decrease of p50. In this pH interval, p50 decreases from 95 to 11 Torr without effectors and from 49 to 6 Torr and from 34 to 5 Torr in the presence of 1 mM urate or caffeine, respectively. Thus, the allosteric effects induced by protons and urate or caffeine are coupled. In contrast, isothermal titration calorimetry did not reveal any differences in binding enthalpy (DeltaH degrees ) for urate or caffeine under either normoxic or hypoxic conditions at different pH values. Despite these apparently conflicting results, they can be explained by the nested MWC model if two different types of modulator binding sites are assumed, an allosteric and a nonallosteric type of site. Simulations of in vivo conditions with this model indicate that the naturally occurring modulator urate is physiologically relevant in H. vulgaris only during hypoxic conditions, i.e., either during environmental oxygen limitation or extensive exercise.     

Sublethal irradiation promotes invasiveness of neuroblastoma cells

Neuroblastoma is the most frequent extracranial solid tumour of childhood. Despite multiple clinical efforts, clinical outcome has remained poor. Neuroblastoma is considered to be radiosensitive, but some clinical studies including the German trial NB90 failed to show a clinical benefit of radiation therapy. The mechanisms underlying this apparent discrepancy are still unclear. We have therefore investigated the effects of radiation on neuroblastoma cell behaviour in vitro. We show that sublethal doses of irradiation up-regulated the expression of the hepatocyte growth factor (HGF) and its receptor c-Met in some neuroblastoma cell lines. The increase in HGF/c-Met expression was correlated with enhanced invasiveness and activation of proteases degrading the extracellular matrix. Thus, irradiation at sublethal doses may promote the metastatic dissemination of neuroblastoma cells through activating the HGF/c-Met pathway and triggering matrix degradation.     

Hydrolysis of low-molecular-weight oligosaccharides and oligosaccharide alditols by pig intestinal sucrase/isomaltase and glucosidase/maltase

The ability of purified pig intestinal sucrase/isomaltase (SI; EC 3.2.1.10/48) and glucosidase/maltase (GM; EC 3.2.1.20) to hydrolyze di- and oligosaccharides consisting of D-glucose and D-fructose residues and the corresponding alditols was studied. The products, after incubation, reflect different binding patterns at both catalytic sites of SI. The active site of the sucrase subunit cleaves alpha,beta-(1-->2) glycosidic bonds, and only two monomer units of the substrates bind with favorable affinity. Oligosaccharides and reduced oligosaccharides containing alpha-(1--6) and alpha-(1-->1) glycosidic bonds are hydrolyzed by isomaltase, and for the active site of this subunit more than two subsites were postulated. Moreover, different binding sites for various aglycons seem to exist for isomaltase. Oligosaccharide alcohols are cleaved at lower rates if the reduced sugar residue occupies the aglycon binding site. GM also hydrolyzes alpha-(1-->1) linkages, but at a lower rate. The enzyme has the ability to bind compounds containing residues other than D-glucose. There are indications for similarities between GM and the isomaltase subunit of SI in the binding mode of oligosaccharides.     

Impact of recombinant baculovirus field applications on a nontarget heliothine parasitoid, Microplitis croceipes (Hymenoptera: Braconidae)

The kill times of two viruses infectious to the heliothine pest complex indigenous to Texas cotton have been significantly reduced by expressing a scorpion toxin gene. Autographa californica nucleopolyhedrovirus (NPV) and Helicoverpa zea NPV express the toxin only in permissive lepidopteran hosts. The toxin, however, could indirectly harm members of upper trophic levels that feed upon and parasitize infected larvae producing the toxin. In this study, the effects of recombinant and wild-type viruses on Microplitis croceipes (Cresson) were studied in cotton using Heliothis virescens (F.) (Lepidoptera: Noctuidae) as hosts. Two recombinant viruses, their two wild-type progenitor viruses, and untreated cotton served as the five treatments of study. Larvae were previously parasitized 2 and 4 d before being confined for 72 h to cotton terminals treated with field rates of virus or left untreated. The sexes of adult M. croceipes that emerged from the recovered H. virescens larvae were determined and their head capsule widths were measured. Polymerase chain reaction (PCR) searched their extracts for virus DNA. There were no differences in percentage emergence and sex ratios of parasitoids among recombinant, wild-type, and control treatments. Significantly more wasps emerged from the 4-d cohort, but these wasps were significantly smaller than wasps from the 2-d cohort regardless of treatment. Finally, PCR found only 15-25% of the recovered H. virescens larvae and none of the emergent M. croceipes had detectable levels of viral DNA. Recombinant and wild-type viruses had a similar, minimal impact on emergent wasps, and the probability of virus dispersal via parasitoids is low in the system tested.     

New evidence for gel-liquid crystalline phase coexistence in the ripple phase of phosphatidylcholines

Experimental evidence supporting the hypothesis of gel-liquid crystalline phase coexistence in the stable ripple phase of diacylphosphatidylcholines has been obtained from time-resolved X-ray small- (SAXS) and wide-angle diffraction (WAXS) in the millisecond to second time domain. The pretransition of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) exhibits a thin lamellar liquid crystalline intermediate phase (designated L_α*) if driven far away from equilibrium by an infrared temperature jump (T-jump) technique. The findings can be described by a two-step model. (1) Instantaneously with the T-jump, an anomalously thin lamellar liquid crystalline intermediate phase (d = 5.6–5.8 nm) forms, coexisting with the original gel-phase L_β′. Within the first seconds, the lamellar repeat distance of the intermediate increases to a value of about 6.7 nm. A closer examination of these kinetics reveals two relaxation components: a fast process, proceeding within tenths of a second, and a slow process, on the time scale of a few seconds. (2) Finally, both the liquid crystalline and the gel-phase relax into the stable ripple phase P_β′. The total process time of the transition is nearly independent of the addition of NaCl, but varies strongly with the chain length of the lecithin species. Received: 24 November 1999 / Revised version: 25 February 2000 / Accepted: 25 February 2000     

Zur Oekologie und Brutbiologie des Rohrschwirls(Locustella luscinioides)

Zusammenfassung In den Jahren 1952 bis 1957 wurde die Entwicklung des Rohrschwirl-Bestandes an den Netteseen (Kreis Kempen-Krefeld) verfolgt. Die Siedlungsdichte erreichte 1956 mit 51 singenden ihren Höchststand.Die Ankunft erfolgte im ersten Aprildrittel, der Nestbau begann im letzten Aprildrittel. Alle aufgefundenen Nester standen inCladium-Horsten. Vollgelege wurden erst nach dem 10. Mai gefunden. Brutdauer 12–13 Tage, Nestlingsdauer 14–16 Tage. Beide Eltern waren am Nestbau und bei der Aufzucht der Jungen beteiligt. Der sichere Nachweis einer Zweitbrut gelang nicht; aber einige Beobachtungen deuten darauf hin, daß Zweitbruten vorkommen.     

Tracking the evolution of porphobilinogen synthase metal dependence in vitro

Metal ions are indispensable cofactors for chemical catalysis by a plethora of enzymes. Porphobilinogen synthases (PBGSs), which catalyse the second step of tetrapyrrole biosynthesis, are grouped according to their dependence on Zn(2+). Using site-directed mutagenesis, we embarked on transforming Zn(2+)-independent Pseudomonas aeruginosa PBGS into a Zn(2+)-dependent enzyme. Nine PBGS variants were generated by permutationally introducing three cysteine residues and a further two residues into the active site of the enzyme to match the homologous Zn(2+)-containing PBGS from Escherichia coli. Crystal structures of seven enzyme variants were solved to elucidate the nature of Zn(2+) coordination at high resolution. The three single-cysteine variants were invariably found to be enzymatically inactive and only one (D139C) was found to bind detectable amounts of Zn(2+). The double mutant A129C/D139C is enzymatically active and binds Zn(2+) in a tetrahedral coordination. Structurally and functionally it mimics mycobacterial PBGS, which bears an equivalent Zn(2+)-coordination site. The remaining two double mutants, without known natural equivalents, reveal strongly distorted tetrahedral Zn(2+)-binding sites. Variant A129C/D131C possesses weak PBGS activity while D131C/D139C is inactive. The triple mutant A129C/D131C/D139C, finally, displays an almost ideal tetrahedral Zn(2+)-binding geometry and a significant Zn(2+)-dependent enzymatic activity. Two additional amino acid exchanges further optimize the active site architecture towards the E.coli enzyme with an additional increase in activity. Our study delineates the potential evolutionary path between Zn(2+)-free and Zn(2+)-dependent PBGS enyzmes showing that the rigid backbone of PBGS enzymes is an ideal framework to create or eliminate metal dependence through a limited number of amino acid exchanges.     

Paradoxical attenuation of leukocyte rolling in response to ischemia- reperfusion and extracorporeal blood circulation in inflamed tissue

In contrast to acute preparations such as the exteriorized mesentery or the cremaster muscle, chronically instrumented chamber models allow one to study the microcirculation under "physiological" conditions, i.e., in the absence of trauma-induced leukocyte rolling along the venular endothelium. To underscore the importance of studying the naive microcirculation, we implanted titanium dorsal skinfold chambers in hamsters and used intravital fluorescence microscopy to study venular leukocyte rolling in response to ischemia-reperfusion injury or extracorporeal blood circulation. The experiments were performed in chambers that fulfilled all well-established criteria for a physiological microcirculation as well as in chambers that showed various extents of leukocyte rolling due to trauma, hemorrhage, or inflammation. In ideal chambers with a physiological microcirculation (<30 rolling leukocytes/mm vessel circumference in 30 s), ischemia-reperfusion injury and extracorporeal blood circulation significantly stimulated leukocyte rolling along the venular endothelium and, subsequently, firm leukocyte adhesion. In contrast, both stimuli failed to elicit leukocyte rolling in borderline chambers (30-100 leukocytes/mm), and in blatantly inflamed chambers with yet higher numbers of rolling leukocytes at baseline (>100 leukocytes/mm), we observed a paradoxical reduction of leukocyte rolling after ischemia-reperfusion injury or extracorporeal blood circulation. A similar effect was observed when we superfused leukotriene B4 (LTB4) onto the chamber tissue. The initial increase in leukocyte rolling in response to an LTB4 challenge was reversed by a second superfusion 90 min later. These observations underscore 1) the benefit of studying leukocyte-endothelial cell interaction in chronically instrumented chamber models and 2) the necessity to strictly adhere to well-established criteria of a physiological microcirculation.