Structure dynamics of the hemoglobin mutants Hb H?tel Dieu, HbG Philadelphia, HbJ Mexico, Hb St. Mandé and Hb San Diego, studied by nanosecond-laser-flash photolysis

The kinetics of the change from the carboxy to the deoxy conformation of the mutated hemoglobins mentioned in the title and of normal human adult hemoglobin were determined from measurements of light absorption changes occurring up to 50 microseconds after nanosecond-laser photodissociation of the corresponding CO complexes. The spectral evolution of the mutated hemoglobins was found to be similar in its main features to that of normal hemoglobin. The kinetics could be decomposed into two phases with rates 1.1-1.8 x 10(6) s-1 and 0.17-0.34 x 10(6) s-1 (except Hb St. Mandé which displayed only the faster phase). Study of the mutated subunits of HbJ Mexico (alpha subunit) and Hb H?tel Dieu (beta subunit) showed that they convert exponentially to the stable deoxy state after photodeligation at the same rates as the corresponding subunits of normal Hb: 1.1 x 10(6) s-1 (alpha) and 0.3 x 10(6) s-1 (beta). The results indicate that there is no direct correlation between the kinetics of spectral relaxation in the time range studied and the oxygenation properties for these hemoglobins. However, there is some indication that the kinetics are dependent upon the region of mutation.     

Crystallographic refinement and structure of ribulose-1,5-bisphosphate carboxylase from Rhodospirillum rubrum at 1.7 A resolution

The amino acid sequence of ribulose-1,5-bisphosphate carboxylase/oxygenase from Rhodospirillum rubrum has been fitted to the electron density maps. The resulting protein model has been refined to a nominal resolution of 1.7 A using the constrained-restrained least-squares refinement program of Sussman and the restrained least-squares refinement program of Hendrickson & Konnert. The crystallographic refinement, based on 76,452 reflections with F greater than sigma (F) in the resolution range 5.5 to 1.7 A resulted in a crystallographic R-factor of 18.0%. The asymmetric unit contains one dimeric ribulose-1,5-biphosphate carboxylase molecule, consisting of 869 amino acid residues and 736 water molecules. The geometry of the refined model is close to ideal, with root-mean-square deviations of 0.018 A in bond lengths and 2.7 degrees in bond angles. Two loop regions, comprising residues 54 to 63 and 324 to 335, and the last ten amino acid residues at the C terminus are disordered in our crystals. The expected trimodal distribution is obtained for the side-chain chi 1-angles with a marked preference for staggered conformation. The hydrogen-bonding pattern in the N-terminal beta-sheet and the parallel sheet in the beta/alpha-barrel is described. A number of hydrogen bonds and salt bridges are involved in domain-domain and subunit-subunit interactions. The subunit-subunit interface in the dimer covers an area of 2800 A2. Considerable deviations from the local 2-fold symmetry are found at both the N terminus (residues 2 to 5) and the C terminus (residues 422 to 457). Furthermore, loop 8 in the beta/alpha-barrel domain has a different conformation in the two subunits. A number of amino acid side-chains have different conformations in the two subunits. Most of these residues are located at the surface of the protein. An analysis of the individual temperature factors indicates a high mobility of the C-terminal region and for some of the loops at the active site. The positions and B-factors for 736 solvent sites have been refined (average B: 45.9 A2). Most of the solvent molecules are bound as clusters to the protein. The active site of the enzyme, especially the environment of the activator Lys191 in the non-activated enzyme is described. Crystallographic refinement at 1.7 A resolution clearly revealed the presence of a cis-proline at the active site. This residue is part of the highly conserved region Lys166-Pro167-Lys168.     

Refined structure of spinach glycolate oxidase at 2 A resolution

The amino acid sequence of glycolate oxidase from spinach has been fitted to an electron density map of 2.0 A nominal resolution and the structure has been refined using the restrained parameter least-squares refinement of Hendrickson and Konnert. A final crystallographic R-factor of 18.9% was obtained for 32,888 independent reflections from 5.5 to 2 A resolution. The geometry of the model, consisting of 350 amino acid residues, the cofactor flavin mononucleotide and 298 solvent molecules, is close to ideal with root-mean-square deviations of 0.015 A in bond lengths and 2.6 degrees in bond angles. The expected trimodal distribution with preference for staggered conformation is obtained for the side-chain chi 1-angles. The core of the subunit is built up from the eight beta-strands in the beta/alpha-barrel. This core consists of two hydrophobic layers. One in the center is made up of residues pointing in from the beta-strands towards the barrel axis and the second, consisting of two segments of residues, pointing out from the beta-strands towards the eight alpha-helices of the barrel and pointing from the helices towards the strands. The hydrogen bond pattern for the beta-strands in the beta/alpha-barrel is described. There are a number of residues with 3(10)-helix conformation, in particular there is one left-handed helix. The ordered solvent molecules are organized mainly in clusters. The average isotropic temperature factor is quite high, 27.1 A2, perhaps a reflection of the high solvent content in the crystal. The octameric glycolate oxidase molecule, which has 422 symmetry, makes strong interactions around the 4-fold axis forming a tight tetramer, but only weak interactions between the two tetramers forming the octamer.     

Preliminary crystallographic data for transketolase from yeast

Crystals of the vitamin B1-dependent enzyme transketolase from baker's yeast have been grown from the apo- and the holoform of the enzyme, using PEG as precipitant. The crystals are orthorhombic, space group P2(1)2(1)2(1) with cell constants a = 76.3 A, b = 114.2 A, and c = 163.5 A. The crystals are stable in the x-ray beam and diffract to at least 2.2 A on a conventional x-ray source. The enzyme is a dimer of identical subunits, and a Vm value of 2.2 A/dalton indicates that the asymmetric unit contains a dimer. Rotation function calculations using native data (10-5 A) revealed a local 2-fold rotation axis with phi = 0 degree and omega = 20 degrees.     

Recombination between satellite phage P4 and its helper P2. I. In vivo and in vitro construction of P4: :P2 hybrid satellite phage

P4::P2 hybrid satellite phages which carry a portion (including the P2 head gene Q and the cohesive end) of the left end of the P2 chromosome linked to the essential part of the P4 chromosome have been isolated by in vivo as well as in vitro recombination. These hybrids express gene Q and grow in the presence of a P2 helper even if defective in gene Q.     

Interleukin-4 downregulates the p70 chain of the IL-2 receptor on peripheral blood mononuclear cells

Data that support a differential regulation of the interleukin-2 receptor (IL-2R) alpha-(p55 or Tac) and beta-chain (p70) expression by IL-4 are presented. Cytofluorometric analysis performed on peripheral blood mononuclear cells, some of which had been nylon wool passed (enriched for T-cells), in the presence or absence of phytohemagglutinin (PHA) or OKT3, demonstrated that IL-4 has a dose-dependent capacity to inhibit beta-chain IL-2R expression, whereas the alpha-chain is nearly unaffected. We could also, as a consequence of the decreased p70 expression, detect a slight increase in the amounts of IL-2 obtained from PHA-stimulated cultures, when IL-4 was present. Further, the proliferative response, especially to IL-2, but also to PHA alone, was depressed in the presence of IL-4. These data thus give further support to the idea that not only the IL-2R complex as such, but also the two individual IL-2R chains, can be independently regulated.     

Enzymatic synthesis and isolation of thymidine diphosphate-6-deoxy-D-xylo-4-hexulose and thymidine diphosphate-L-rhamnose. Production using cloned gene products and separation by HPLC.

A two-step enzymatic synthesis of dTDP-L-rhamnose is developed using enzymes from sonicated extracts of cultures of Escherichia coli K12 strains harboring plasmids containing different parts of the rfb gene cluster of Salmonella enterica LT2. The intermediate dTDP-6-deoxy-D-xylo-4-hexulose was isolated after a 1-h reaction, using only dTDP-D-glucose and dTDP-D-glucose 4,6-dehydratase, followed by protein precipitation and desalting by gel chromatography (yield 89%). In a two-step reaction using dTDP-D-glucose and dTDP-D-glucose 4,6-dehydratase in the first step, and with NADPH, dTDP-6-deoxy-D-xylo-4-hexulose 3,5-epimerase and NADPH:dTDP-6-deoxy-L-lyxo-4-hexulose-4-reductase in the second hour of incubation, the dTDP-D-glucose was fully converted to dTDP-L-rhamnose. The hexoses of both products were identified by mass spectroscopy. The molar yield of dTDP-L-rhamnose, after protein precipitation, anion-exchange chromatography and desalting by gel chromatography, was 62%, corresponding to more than 150 mg, starting from 250 mg of dTDP-D-glucose. When stored lyophilysed under nitrogen, these products were found to be stable for several months. Both dTDP-6-deoxy-D-xylo-4-hexulose and dTDP-L-rhamnose have light absorption maxima at 267 nm, with molar absorption coefficients close to that of dTMP. However, the absorption coefficient of dTDP-6-deoxy-D-xylo-4-hexulose at the absorption maximum of 320 nm (specific for sugars containing keto groups) was found to be approximately 20% higher than values presented earlier. Furthermore, an HPLC technique is presented for determining the net activity of dTDP-6-deoxy-D-xylo-4-hexulose 3,5-epimerase and NADPH:dTDP-6-deoxy-L-lyxo-4-hexulose-4-reductase, based on separation of dTDP-6-deoxy-D-xylo-4-hexulose and dTDP-L-rhamnose. The HPLC technique is also suitable for determination of all the nucleotide components involved in the synthesis.