PubMed Health⌕ Search

Biomedical subjects

A Lenz

Publications and source records attributed to A Lenz.

29 records · Page 2Linked to original sources
PubMed1991

X-ray analysis of cubic crystals of the complex formed between ribonuclease T1 and guanosine-3',5'-bisphosphate.

The complex formed between ribonuclease T1 (RNase T1) and guanosine-3',5'-bisphosphate (3',5'-pGp) crystallizes in the cubic space group I23 with alpha = 86.47 (4) A. X-ray data were collected on a four-circle diffractometer to 3.2 A resolution and the structure was determined by molecular-replacement methods [ULTIMA; Rabinovich & Shakked (1984). Acta Cryst. A40, 195-200] based on the RNase T1 coordinates taken from the complex with guanosine-2'-phosphate. Refinement converged at 16.6% for 1540 data with Fo greater than 1 sigma (Fo) with acceptable stereochemistry. The RNase T1 conformation is comparable to that in other complexes which crystallize preferentially in space group P2(1)2(1)2(1) except for side chains that interact intermolecularly. The guanine of 3',5'-pGp is bound to the recognition site in the same way as in other guanine-containing complexes except for its interaction with Glu46. The side-chain carboxylate of this amino acid does not form hydrogen bonds to N1H and N2H of guanine but is rotated so as to permit insertion of two water molecules which replace its acceptor functions. In contrast to other guanosine derivatives which are bound to RNase T1 in the syn form, 3',5'-pGp is anti. This conformation positions the two phosphate groups 'outside' the protein, with hydrogen-bonding contacts only to water molecules; the active site is filled by water. The RNase T1-3',5'-pGp complex probably has biological significance as it may represent the enzyme-product complex before dissociation.

Aspergillus oryzae↗
PubMed1991

Evidence for a substrate-binding subsite in ribonuclease T1. Crystal structure of the complex with two guanosines, and model building of the complex with the substrate guanylyl-3',5'-guanosine.

The enzyme ribonuclease T1 cleaves single-stranded RNA at the 3'-side of guanosine. The structure of the complex with two guanosines has been analyzed at 1.8-A resolution and refined to a crystallographic R value of 14.0%. One guanosine occupies the guanosine recognition site as observed in previously analyzed complexes of ribonuclease T1 with guanosine phosphates. The other is bound to a base-unspecific subsite marking the binding locus of the nucleoside 3'-proximal to guanosine in a cleavable RNA chain. The positions of the guanosine bound to the recognition site and of the guanine base at the subsite were used to guide model building of the substrate guanylyl-3',5'-guanosine bound to the active site of ribonuclease T1. After energy minimization and a 7-ps stochastic dynamics simulation, a plausible model of the enzyme-substrate complex was obtained which may serve as a reference point in consideration of the mechanisms of RNA hydrolysis by ribonuclease T1.

Crystallization↗
PubMed1990

Disappearance of certain acidic organelles (endosomes and Langerhans cell granules) accompanies loss of antigen processing capacity upon culture of epidermal Langerhans cells.

Freshly isolated epidermal Langerhans cells (LC) can actively process native protein antigens, but are weak in sensitizing helper T cells. During culture, when LC mature into potent immunostimulatory dendritic cells, T cell sensitizing capacity develops but antigen processing capacity is downregulated. Processing of exogenous antigens for class II-restricted antigen presentation involves acidic organelles. We used the DAMP-technique to monitor acidic organelles at the ultrastructural level in fresh, as well as cultured, mouse and human LC. We observed that the loss of antigen processing capacity with culture of LC was reflected by the disappearance of certain acidic organelles, namely endosomes (particularly early ones), and the hitherto enigmatic LC granules ("Birbeck Granules"). Our findings support the notion that endosomes are critical for antigen processing and suggest that LC granules might be involved as well.

Animals↗
PubMed1990

Interaction between hepatitis B surface proteins and monomeric human serum albumin.

HBsAg is known to bind to human serum albumin polymerized by glutaraldehyde, human serum albumin has been found in preparations of HBsAg by several investigators. However, it is not yet known whether natural human serum albumin binds to hepatitis B virus under physiological conditions. We studied the binding between natural or recombinant HBsAg and monomeric human serum albumin by immunological, biochemical and biophysical methods. The binding capacity of 20-nm HBs spheres was variable but ranged up to six molecules HSA/sphere. A reversible binding site for human serum albumin was exclusively localized in the preS2 domain, whereas the S domain was inactive in vitro. Human serum albumin copurified with HBsAg of human origin during gel chromatography or sucrose-gradient centrifugation. This human serum albumin was monomeric in sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The preS2-bound part of the human serum albumin could be removed from HBsAg by high-salt, such as CsCl centrifugation, but another part could only be removed by treatment with a disulfide cleaving reagent. Most of this covalently bound human serum albumin was retained at the HBsAg particle after complete cleavage of medium-sized HBs protein with trypsin. This indicates a second way in which albumin binds irreversible to cysteine(s) of the small HBs protein (SHBs, P24 and GP27).

Chemical Fractionation↗
PubMed1989

Murine epidermal Langerhans cells express significant amounts of class I major histocompatibility complex antigens.

Epidermal Langerhans cells (LC) are leukocytes that express major histocompatibility complex (MHC) class II antigens and function as antigen-presenting and accessory cells. Caughman et al. [Caughman, S. W., Sharrow, S. O., Shimada, S., Stephany, D., Mizuochi, T., Rosenberg, A. S., Katz, S. I. & Singer, A. (1986) Proc. Natl. Acad. Sci. USA 83, 7438-7442] reported that LC are deficient in surface expression of MHC class I antigens, implying a specialization of these cells to class II-restricted antigen presentation. To readdress this obviously important issue, we have studied murine epidermal sheets prepared from B6 X BALB/c----B6 bone marrow chimeras 5 months after irradiation and bone marrow reconstitution. This enabled us to distinguish class I of LC from that of surrounding keratinocytes. When sheets were analyzed by immunofluorescence microscopy with monoclonal antibodies specific for donor class I antigens, donor-derived LC but not LC of recipient origin were stained. Appropriate controls for antibody isotype and MHC haplotype were negative. LC in epidermal cell suspensions, prepared from normal BALB/c and BALB/cBy mice (MHC haplotype d), were analyzed by flow cytometry as well as immunofluorescence microscopy. LC were stained by monoclonal antibodies to class I antigens of haplotype d, but not by isotype-matched control antibodies to class I antigens of haplotype k. We also found that LC were virtually depleted from epidermal cell suspensions by treatment with monoclonal antibodies to class I antigens of haplotype d and complement but not by treatment with control monoclonal antibodies and complement. Our data, therefore, show that LC express MHC class I molecules on their surface.

Animals↗
PubMed1989

Cultured human Langerhans cells resemble lymphoid dendritic cells in phenotype and function.

Freshly isolated murine epidermal Langerhans cells (LC) are weak stimulators of resting T cells. Upon culture their phenotype changes, their stimulatory activity increases significantly, and they come to resemble lymphoid dendritic cells. Resident murine LC, therefore, might represent a reservoir of immature dendritic cells. We have now used enzyme cytochemistry, a panel of some 80 monoclonal antibodies, and immunofluorescence microscopy or two-color flow cytometry, as well as transmission electron microscopy, to analyse the phenotype and morphology of human LC before and after 2-4 d of bulk epidermal cell culture. In addition, LC were enriched from bulk epidermal cell cultures, and their stimulatory capacity was tested in the allogeneic mixed leukocyte reaction and the oxidative mitogenesis assay. Cultured human LC resembled human lymphoid dendritic cells in morphology, phenotype, and function. Specifically, LC became non-adherent upon culture and developed sheet-like processes (so-called "veils"), decreased their surface ATP/ADP'ase activity, and lost nonspecific esterase activity. As in the mouse, surface expression of MHC class I and II antigens increased significantly, and FcII receptors were significantly reduced. Markers that are expressed by dendritic cells (like CD40) appeared on LC following culture. Cultured human LC were potent T-cell stimulators. Our findings support the view that resident human LC, like murine LC, represent immature precursors of lymphoid dendritic cells in skin-draining lymph nodes.

Antibodies, Monoclonal↗
PubMed1989

Laser spectrophotometry in the fetus.

Laser spectrophotometry with near-infrared light is newly available for clinical application. The equipment consists of a near-infrared datacollection unit (NIRDCU) and apersonal computer. Emission of laser light at wavelengths of 775, 805, 845 and 904 nm is provided by the four laserdiodes of the NIRDCU. By analyzing changes of optical density during laser radiation, information is achieved about the intracellular redoxstate and relative changes of blood volume. During measurement with the system on fetal head we were able to get a first impression of the methods potential. While the application of the laser sensors is still cumbersome, signals providing information of the relative changes of hemoglobine concentrations, relative changes of blood volume and cytochrome aa3 seem achievable. Laser spectrophotometric monitors may become save, low cost and portable instruments for the noninvasive assessment of the biochemical and biophysical status in the fetus.

Fetal Monitoring↗
PubMed1987

[Serologic AIDS diagnosis with polypeptides obtained by genetic technics of the human immunodeficiency virus (HIV-1)].

Serologic testing for human immunodeficiency virus type 1 (HIV-1) is currently based on enzyme linked immunosorbent assay (ELISA) as screening method. Positive ELISA-results have to be confirmed by at least one second procedure such as Western blotting or immunofluorescence. To obtain new diagnostic reagents for confirmatory testing, we expressed viral antigens in procaryotic systems. Peptides representing epitopes of structural core (gag)- and envelope (env)-proteins of HIV were produced in E. coli as stable immunogenic beta-galactosidase fusion proteins. Recombinant proteins were taken for immunoblot-assays. The results of Western blotting with those fusion proteins were in general comparable with conventional ELISA, immunofluorescence, immunoblot with cell-culture derived virus and commercially available ELISA tests based on recombinant proteins. Immunoblots using recombinant transmembrane protein (gp41) derived polypeptide were more sensitive than the conventional procedure with purified virion proteins. Western blotting with recombinant fusionproteins provide reliable and inexpensive serodiagnostics without handling of infectious cell cultures.

Acquired Immunodeficiency Syndrome↗
PubMedDate not supplied

[Laser spectroscopy in the newborn infant--initial experiences].

Equipment for near-infrared laserspectroscopy for clinical application is newly available. By this technique noninvasive monitoring of biochemical parameters is achievable. We report on our first experience with a Radiometer prototype for such NIR laserspectroscopy during measurements in 5 neonates. Laserdiodes provide emission at a wavelength of 775, 805, 845 and 904 nm. The registered signals are computerized aiming at a calculation of relative changes of saturated and unsaturated hemoglobine, changes in blood volume and cytochrome aa-3. In this article graphical display of the parameters give insights in the redoxstate and the hemodynamics of the biological sample. The near-infrared laserspectroscopy has the potential of becoming an instrument for the study of biophysical and biochemical alterations in the newborn.

Brain Damage, Chronic↗