Biomedical subjects

R Kinder

Publications and source records attributed to R Kinder.

7 recordsLinked to original sources

PubMed2000

Membrane interactions and alignment of structures within the HIV-1 Vpu cytoplasmic domain: effect of phosphorylation of serines 52 and 56.

The cytoplasmic domain of the HIV-1 accessory protein Vpu is involved in the binding and degradation of the viral receptor CD4. In order to analyze previous structural models in the context of membrane environments, regions of Vpu(CYTO) incorporating particular conformational features have been synthesized and labelled with (15)N at selected backbone amides. Well-oriented proton-decoupled (15)N solid-state NMR spectra with (15)N chemical shifts at the most upfield position indicate that the amphipathic helix within [(15)N-Leu 45]-Vpu(27-57) strongly interacts with mechanically aligned POPC bilayers and adopts an orientation parallel to the membrane surface. No major changes in the topology of this membrane-associated amphipathic helix were observed upon phosphorylation of serine residues 52 and 56, although this modification regulates biological function of Vpu. In contrast, [(15)N-Ala 62]-Vpu(51-81) exhibits a pronounced (15)N chemical shift anisotropy.

Human Immunodeficiency Virus Proteins↗

PubMed1999

Solution structure and orientation of the transmembrane anchor domain of the HIV-1-encoded virus protein U by high-resolution and solid-state NMR spectroscopy.

The structure of the membrane anchor domain (VpuMA) of the HIV-1-specific accessory protein Vpu has been investigated in solution and in lipid bilayers by homonuclear two-dimensional and solid-state nuclear magnetic resonance spectroscopy, respectively. Simulated annealing calculations, using the nuclear Overhauser enhancement data for the soluble synthetic peptide Vpu1-39 (positions Met-1-Asp-39) in an aqueous 2,2,2-trifluoroethanol (TFE) solution, afford a compact well-defined U-shaped structure comprised of an initial turn (residues 1-6) followed by a linker (7-9) and a short helix on the N-terminal side (10-16) and a further longer helix on the C-terminal side (22-36). The side chains of the two aromatic residues (Trp-22 and Tyr-29) in the longer helix are directed toward the center of the molecule around which the hydrophobic core of the folded VpuMA is positioned. As the observed solution structure is inconsistent with the formation of ion-conductive membrane pores defined previously for VpuMA in planar lipid bilayers, the isolated VpuMA domain as peptide Vpu1-27 was investigated in oriented phospholipid bilayers by proton-decoupled 15N cross polarization solid-state NMR spectroscopy. The line widths and chemical shift data of three selectively 15N-labeled peptides are consistent with a transmembrane alignment of a helical polypeptide. Chemical shift tensor calculations imply that the data sets are compatible with a model in which the nascent helices of the folded solution structure reassemble to form a more regular linear alpha-helix that lies parallel to the bilayer normal with a tilt angle of </=30 degrees. The arrangement of the membrane-associated structures described previously for the cytoplasmic domain and for the anchor domain of Vpu identified in this work is discussed.

Amino Acid Sequence↗

PubMed1999

Peptide structural analysis by solid-state NMR spectroscopy.

Solid-state nmr spectroscopy provides a robust method for investigating polypeptides that have been prepared by chemical synthesis and that are immobilized by strong interactions with solid surfaces or large macroscopic complexes. Solid-state nmr spectroscopy has been widely used to investigate membrane polypeptides or peptide aggregates such as amyloid fibrils. Whereas magic angle spinning solid-state nmr spectroscopy allows one to measure distances and dihedral angles with high accuracy, static membrane samples that are aligned with respect to the magnetic field direction allow one to determine the secondary structure of bound polypeptides and their orientation with respect to the bilayer normal. Peptide dynamics and the effect of polypeptides on the macroscopic phase preference of phospholipid membranes have been investigated in nonoriented samples. Investigations of the structure and topology of membrane channels, peptide antibiotics, signal sequences as well as model systems that allow one to dissect the interaction contributions in phospholipid membranes will be presented in greater detail.

Anti-Bacterial Agents↗

PubMed1999

The alignment of a voltage-sensing peptide in dodecylphosphocholine micelles and in oriented lipid bilayers by nuclear magnetic resonance and molecular modeling.

The S4 segments of voltage-gated sodium channels are important parts of the voltage-sensing elements of these proteins. Furthermore, the addition of the isolated S4 polypeptide to planar lipid bilayers results in stepwise increases of ion conductivity. In order to gain insight into the mechanisms of pore formation by amphipathic peptides, the structure and orientation of the S4 segment of the first internal repeat of the rat brain II sodium channel was investigated in the presence of DPC micelles by multidimensional solution NMR spectroscopy and solid-state NMR spectroscopy on oriented phospholipid bilayers. Both the anisotropic chemical shift observed by proton-decoupled (15)N solid-state NMR spectroscopy and the attenuating effects of DOXYL-stearates on TOCSY crosspeak intensities of micelle-associated S4 indicate that the central alpha-helical portion of this peptide is oriented approximately parallel to the membrane surface. Simulated annealing and molecular dynamics calculations of the peptide in a biphasic tetrachloromethane-water environment indicate that the peptide alpha-helix extends over approximately 12 residues. A less regular structure further toward the C-terminus allows for the hydrophobic residues of this part of the peptide to be positioned in the tetrachloromethane environment. The implications for possible pore-forming mechanisms are discussed.

Amino Acid Sequence↗

PubMed1997

Gamma-irradiation and UV-C light-induced lipid peroxidation: a Fourier transform-infrared absorption spectroscopic study.

Fourier transform-infrared spectroscopy of dry, multibilayer films has been used to study gamma-radiation and UV-C light induced lipid peroxidation in 1,2-dilinoleoyl-sn-glycero-3-phosphocholine liposomes. The observed spectral changes were compared with the results obtained from measurement of hydroperoxides, conjugated dienes and to the formation of thiobarbituric acid reactive substances, such as malondialdehyde (MDA) or MDA-like substances. Upon irradiation a decrease in intensity of the asymmetric C - H stretching vibration (va(CH2)) of the isolated cis C = C - H groups (3010 cm-1) was observed. Directly correlated with the decrease of the va(CH2) absorption was a shift of the asymmetric phosphate ester stretching vibration (va(P = O)) towards smaller wavenumbers (1260-->1244 cm-1), indicating that the lipid peroxidation induced molecular alterations in the fatty acid chains influence the packing of the phospholipids in dry multibilayer films. In addition, the formation of a new absorption band at 1693 cm-1 could be detected, the intensity of which was comparable with the formation of thiobarbituric acid reactive substances and, therefore, attributed to the (C = O) stretching of alpha, beta unsaturated aldehydes. Dose-dependent studies using ionizing radiation showed that the decrease of va(CH2) was directly correlated with an increase in absorption of the conjugated dienes at 234 nm and with the formation of hydroperoxides suggesting that the absorption at 3010 cm-1 is solely due to isolated cis C = C - H groups and hence subject to the early stages of the radical chain reaction. UV-C light induced lipid peroxidation revealed a non-linear decrease of I3010, which was directly correlated with the formation of hydroperoxides. The observed early saturation of the conjugated dienes was attributed to an early photodecomposition of the conjugated double bonds.

Gamma Rays↗

PubMed1997

Unsuspected rectal adenocarcinoma causing a urinoma.

A middle-aged man with a history of Hodgkin's disease presented with loin pain and microscopic hematuria. Radiologic studies demonstrated a urinoma secondary to ureteric obstruction at the pelvic brim. Percutaneous nephrostomy was performed to decompress the collection and a ureteric stent inserted to maintain drainage. Laparotomy revealed an unsuspected rectal adenocarcinoma. A metastatic deposit compressing the ureter had produced the urinoma. Metastatic colorectal carcinoma is a rare cause of urinoma.

Adenocarcinoma↗

PubMed1996

UV-B-induced cell cycle perturbations, micronucleus induction, and modulation by caffeine in human keratinocytes.

UV-B-induced perturbations of cell cycle progression in asynchronous human keratinocytes were analysed during two cell cycles with respect to their cell cycle stage at the time of irradiation using BrdUrd/Hoechst flow cytometry. Exponentially growing SCL-2-keratinocytes exposed to UV-B radiation showed a short delay in G1-phase exit and were blocked in the S and G2/M phases of the first cell cycle. UV-A wavelengths did not show any detectable effect on cell cycle progression. In contrast, 137Cs-irradiation of these cells induced a temporary G2 block only. Micronucleus frequency increased in gamma-irradiated cells as soon as the cells started to divide and reached a plateau when most of the cells had divided. Continuous treatment with caffeine starting immediately after 137Cs gamma-irradiation prevented accumulation of cells in G2 phase, but did not influence the frequency of micronuclei. In UV-B-irradiated keratinocytes, however, the damage-induced cell cycle perturbations were merely reduced by caffeine, but not eliminated. Compared with gamma-irradiation a moderate induction of micronuclei was observed in UV-B-irradiated cells. Caffeine, however, potentiated the induction of micronuclei by UV-B. These different effects on cell cycle kinetics and micronucleus induction indicate different mechanisms of DNA damage caused by UV-B- and gamma-irradiation that may be repaired through different pathways.

Caffeine↗