Conformational studies of a benzodiazepine-like peptide in SDS micelles by circular dichroism, 1H NMR and molecular dynamics simulation

The conformation of a benzodiazepine-like decapeptide corresponding tothe YLGYLEQLLR fragment of a casein has been examined in a sodium dodecylsulfate micellar medium using circular dichroism, two-dimensional¹H NMR spectroscopy and restrained molecular dynamicssimulation. The decapeptide adopts an amphipathic 3₁₀-helicoidstructure in which theE⁶···R¹⁰ ionic bridgestabilizes the C-terminus.     

Topological analysis of the membrane-bound glucosyltransferase, MdoH, required for osmoregulated periplasmic glucan synthesis in Escherichia coli.

The MdoH protein is essential for synthesis of the osmoregulated periplasmic glucans, known as membrane-derived oligosaccharides (MDOs), in Escherichia coli. Mutants lacking MdoH are deficient in a glucosyltransferase activity assayed in vitro. The MdoH protein is the product of the second gene of an operon, and it has been shown to span the cytoplasmic membrane. The MdoH protein comprises 847 amino acids and is poorly expressed as observed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. We have experimentally measured the topological organization of MdoH within the membrane by construction of fusions to beta-lactamase as a reporter. Analysis of 51 different MdoH-beta-lactamase fusions suggested that the MdoH protein crosses the cytoplasmic membrane eight times, with the N and C termini in the cytoplasm. Moreover, a 310-amino-acid domain is present in the cytoplasm between the second and third transmembrane segments. It was deduced from the measurement of the MDO biosynthetic activity of truncated or fused MdoH proteins that almost all the C-terminal residues are necessary for this activity. The model of the MdoH protein in the membrane suggests that this protein could be directly involved in the translocation of nascent polyglucose chains to the periplasmic space.     

Sperm motility in turbot,Scophthalmus marimus: initiation of movement and changes with time of swimming characteristics

Synopsis Turbot sperm motility is observed using dark field microscopy and stroboscopic illumination combined with video recording. Sperm motility is triggered by dilution of spermatozoa in sea water or in non ionic media (glucose or saccharose), presenting osmotic pressure ranging from 300 to 2100 mOsmol. The percentage of motile spermatozoa reaches 100% under conditions of osmotic pressure of 300 to 1100 mOsmol and pH close to 8.0. In full sea water, glucose or saccharose solutions an agglutination of spermatozoa is observed; this is prevented by addition of bovine serum albumin (5 mg ml^–1). Immediately after transfer in activation solutions, 100% spermatozoa are motile in most samples freshly stripped. This percentage drops suddenly between 15 and 30% after 70 to 100 sec. The beat frequency remains at a constant value of 50 Hz during 40 s post activation and then drops suddenly between 15 and 30 Hz. The spermatozoa velocity is about 200 micrometers s^–1 during 30 to 40 s and then declines to a stable value of 100 micrometers s^–1 at 50 s post activation. After 1.20 mn, more and more spermatozoa become motionless. The minimum calculated and averaged distance covered during 1.20 min, is about 12 mm. The high performances of turbot spermatozoa motility are interpreted as a compensatory mechanism for the low sperm production.     

Multiple modes of ligand recognition: Crystal structures of cyclin-dependent protein kinase 2 in complex with ATP and two inhibitors,olomoucine and isopentenyladenine

Cyclin-dependent kinases (CDKs) are conserved regulators of the eukaryotic cell cycle with different isoforms controlling specific phases of the cell cycle. Mitogenic or growth inhibitory signals are mediated, respectively, by activation or inhibition of CDKs which phosphorylate proteins associated with the cell cycle. The central role of CDKs in cell cycle regulation makes them a potential new target for inhibitory molecules with anti-proliferative and/or anti-neoplastic effects. We describe the crystal structures of the complexes of CDK2 with a weakly specific CDK inhibitor, N6-(δ2-isopentenyl)adenine, and a strongly specific inhibitor, olomoucine. Both inhibitors are adenine derivatives and bind in the adenine binding pocket of CDK2, but in an unexpected and different orientation from the adenine of the authentic ligand ATP. The N6-benzyl substituent in olomoucine binds outside the conserved binding pocket and is most likely responsible for its specificity. The structural information from the CDK2-olomoucine complex will be useful in directing the search for the next generation inhibitors with improved properties. © 1995 Wiley-Liss, Inc.     

pAMβ1 resolvase has an atypical recombination site and requires a histone-like protein HU

The broad-host-range plasmid pAMβ1 from Gram-positive bacteria encodes a resolvase, designated Resβ, which shares homology with the proteins of the resolvase—invertase family. Here we report the purification and in vitro characterization of Resβ. This resolvase is particular in two aspects: it has an atypical binding site and requires a cofactor to promote resolution in vitro . Resβ binds to two regions within its resolution site res . One contains two inverted repeats (R1 and R2), the other contains only one repeat (R3). The cofactor required for resolution in vitro is present in crude extracts of both Bacillus subtilis and Escherichia coli and can be substituted by the E. coli histone-like protein HU. The possible mode of action of HU in the resolution process is discussed.     

A three-step purification of human alpha 1-acid glycoprotein

alpha 1-Acid glycoprotein (AGP) was purified to homogeneity by a 3-step procedure using pseudo-ligand affinity chromatography on immobilized Cibacron blue F3GA, Procion red HE3B, and preparative column isoelectric focusing. The overall yield of the combined techniques was 88%. Analysis of the purified AGP by lectin affinity chromatography on immobilized Con A and immunoaffino-electrophoresis indicated that the most acidic form did not interact with the lectin, while the two more basic fractions possessed different affinities for Con A. In addition, 3 different populations of AGP were clearly separated by Con A affinity chromatography.     

Studies in vitro on the uptake and degradation of sodium hyaluronate in rat liver endothelial cells.

Rat liver endothelial cells in primary cultures at 7 degrees C bind radioactively labelled sodium hyaluronate (HA; Mr 400 000) specifically and with high affinity (Kd = 6 X 10(-11) M). Maximal binding capacity is approx. 10(4) molecules per cell. Inhibition experiments with unlabelled HA and oligosaccharides from HA indicate that each molecule is bound by several receptors acting co-operatively and that the single receptor recognizes a tetra- or hexa-saccharide sequence of the polysaccharide. At 37 degrees C the liver endothelial cells endocytose the HA. The process combines the features of a receptor-mediated and a fluid-phase endocytosis. The rate of internalization does not show any saturation with increasing HA concentration, but is approximately proportional to the polysaccharide concentration at and above the physiological concentration. At 50 micrograms of free HA/l each liver endothelial cell accumulates 0.1 fg of the polysaccharide/min. Fluorescent HA accumulates in perinuclear granules, presumably lysosomes. Degradation products from HA appear in the medium about 30 min after addition of the polysaccharide to the cultures. The radioactivity from HA containing N-[3H]acetyl groups or 14C in the sugar rings is recovered mainly as [3H]acetate and [14C]acetate respectively. Estimations of the capacity of liver endothelial cells to internalize and degrade HA in vitro indicate that these cells may be primarily responsible for the clearance of HA from human blood in vivo.