Search

Background: The interfacial activation of lipases results primarily from conformational changes in the enzymes which expose the active site and provide a hydrophobic surface for interaction with the lipid substrate. Comparison of the crystallization conditions used and the structures observed for a variety of lipases suggests that the enzyme conformation is dependent on solution conditions. Pseudomonas cepacia lipase (PCL) was crystallized in conditions from which the open, active conformation of the enzyme was expected. Its three-dimensional structure was determined independently in three different laboratories and was compared with the previously reported closed conformations of the closely related lipases from Pseudomonas glumae (PGL) and Chromobacterium viscosum (CVL). These structures provide new insights into the function of this commercially important family of lipases. Results: The three independent structures of PCL superimpose with only small differences in the mainchain conformations. As expected, the observed conformation reveals a catalytic site exposed to the solvent. Superposition of PCL with the PGL and CVL structures indicates that the rearrangement from the closed to the open conformation involves three loops. The largest movement involves a 40 residue stretch, within which a helical segment moves to afford access to the catalytic site. A hydrophobic cleft that is presumed to be the lipidbinding site is formed around the active site. Conclusions: The interfacial activation of Pseudomonas lipases involves conformational rearrangements of surface loops and appears to conform to models of activation deduced from the structures of fungal and mammalian lipases. Factors controlling the conformational rearrangement are not understood, but a comparison of crystallization conditions and observed conformation suggests that the conformation of the protein is determined by the solution conditions, perhaps by the dielectric constant.

Subtilisin BPN’ (BPN) is an industrially important serine protease that has been extensively investigated in many laboratories. In an effort to improve the thermal stability of the enzyme, researchers at Procter & Gamble have used site-directed mutagenesis techniques to produce several variants of BPN in which residues at the surface of the enzyme have been substituted. We initiated crystallographic studies to determine the structural consequences of these amino acid substitutions. In the course of this work we obtained excellent crystals that correspond to the C2 crystal form of native BPN that has been previously reported.1 Since the structure reported in that work was of only medium resolution, high-resolution X-ray data for this crystal form of native BPN have been collected and the refinement of the structure has been extended using these new data. Isomorphous crystals of two variants, Q19E and Q271E, have also been grown, high-resolution X-ray data have been collected for these crystals, and the experimental results are described. The structures of the native enzyme and the Q271E variant have been refined and are described.

This presentation provides a change of direction in several respects relative to the other presentations in this symposium. First, rather than dealing with small chemical molecules, I will be considering complex biological macromolecules. Second, whereas the research described in the other presentations has typically been based on limited amounts of data, protein crystal structure determinations require vast amounts of data (from 15,000 to 25,000 independent measurements for a 30 kDa protein structure at 2.0 A resolution). Third, the compounds reported in the other presentations are relatively stable both chemically and with respect to ionizing radiation. But proteins are highly sensitive to both chemical and radiation-induced degradation. And finally, this presentation will describe a general strategy to use synchrotron X-radiation to solve industrially important protein structures, whereas the other presentations have provided detailed case studies of how synchrotron X-ray data have been used to address industrially important problems.

The neutral lipase from the bacteria Pseudomonas fluorescens, marketed under the trade name LpL-200S, has been crystallized in a form suitable for X-ray diffraction analysis from 35% n-propanol at pH 8·5. The crystals are monoclinic prisms and are of space group C2 with a = 91·00 A ̊, b = 47·17 A ̊, c = 35·21 A ̊ and β = 121·43 °. There is one molecule of the protein as the asymmetric unit of the crystals. The diffraction pattern extends to at least 1·6 Å resolution and the crystals are extremely robust in terms of X-ray exposure. © 1991.

RuX 2 (Me 2 SO)[EtS(CH 2 ) 3 SO(CU 2 ) 3 SEt] avec X=Cl, Br. Les deux composes cristallisent dans le systeme monoclinique, groupe d'espace P2 1 et leur structure est affinee jusqu'a R=0,023 et R=0,030 respectivement

Structures cristallines des deux formes polymorphes du [Rh ((R)-Cycphos) (norbornadiene)] ClO 4 . Mise en evidence d'orientation differente des cycles phenyle et cyclohexyle. Complexes plan carre. Relation entre resultats cristallographiques et mecanisme d'hydrogenation asymetrique

Die in MeOH bei 35°C durchgefuhrte Titeloxidation, in der das koordinierte Thiolat nucleophil angreift, liefert den Komplex (Ia), der mit Z=4 in der RG P21/c kristallisiert.

The crystal structure of methyl[hydrotris(pyrazol-1-yl)borato]carbonylplatinum(II) has been determined by single crystal X-ray diffraction techniques. Crystals of (CH3)[HB(C3N2H3)3]Pt(CO) are monoclinic, P21/c,a = 14.416(1), b = 7.951(1), c = 12.990(1) A, β = 104.35(1)°. The observed density (2.04 g cm−3) agrees favorably with that calculated (2.08 g cm−3) on the basis of four molecules per unit cell. The structure was solved by the Patterson method and has been refined by full-matrix least squares techniques to a final R1 value of 0.041 (R2 = 0.039) for 2124 reflections. The compound is square-planar with only two of the three pyrazolyl groups coordinated to the platinum atom. The platinum atom is located 0.015(1) A above the plane defined by the four donor atoms. The uncoordinated pyrazolyl group is disordered with the shortest intramolecular distance involving platinum and any non-hydrogen atom of that ring being 3.30(1) A. The PtN distances are 2.036(9) and 2.064(9) A; PtC(methyl) and PtC(carbonyl) distances are 2.070(12) and 1.798(16) A, respectively.

The structure of o -(diphenylphosphino) phenyl- cis -1,2-dicarbomethoxyethenyltriphenylphosphineplatinum,(Ph3P)[Ph2P(C6H4)]Pt- cis -(CO2MeCCHCO2Me), has been determined by single crystal X-ray diffraction methods. The crystals are triclinic, space group P 1 , two molecules per unit cell with dimensions a = 12.560(1), b = 13.600(1), c = 11.452(1) A, α = 110.01(1), β = 97.58(1), and γ = 91.03(1)°. A calculated density of 1.57 g cm−3 for two formula units per cell is consistent with the measured value of 1.56(2) g cm−3. The coordination about the platinum atom is square-planar with the two phosphine ligands oriented cis with respect to one another. The σ-bonded vinyl group also possesses cis stereochemistry. The geometry of the four-atom metallocyclic ring in this compound is compared to those of metallocyclobutene and platinacyclobutane complexes. The average PtP bond length is 2.330(2) A and the observed PtC bond lengths are 2.059(8) and 2.026(8) A. These bond lengths are discussed in terms of the trans -influence. Full-matrix least-squares refinement has yielded R = 0.047 (0.048 for weighted R) based on the 5208 reflections whose intensities are significantly above background (Inet ≥ 10 counts s−1).

The crystal structure of hexafluoroacetone azine bis(triphenylphosphine)platinum, C42H30F12N2P2Pt, has been determined by single-crystal X-ray diffraction techniques. The compound crystallizes in the monoclinic space group C2/c with a 31.155(3), b 13.091(1), c 21.828(2) A, β 109.23(1)° and Z = 8. Manual diffractometer methods (Cu radiation, λ 1.54050 A) were used to obtain 5046 reflections with Inet ⩾ 8 counts sec−1 at 21°C. The structure was solved by the heavy atom method and was refined, including CH2Cl2 at occupancy 0.4 on a crystallographic 2-fold axis, by block-diagonal least-squares methods to R = 0.056. Location of the phenyl hydrogen atoms was not attempted. The platinum atom is σ-bonded to one CN of the azine ligand forming a PtCN three-membered ring. Coordination about platinum consists of a slightly distorted square-planar arrangement of the phosphorus atoms and the bonded carbon and nitrogen atoms of the unsaturated ligand. The observed difference in PtP bond lengths is rationalized in terms of the trans-influence.

Infrared spectra were obtained for methallyl iodide (3-iodo-2-methylpropene)in the liquid state at room temperature and for the vapor state at a series of temperatures. The spectra show that this compound exists in only one form in the neat liquid at room temperature. In the vapor, the concentration of a second form becomes appreciable at elevated temperatures. The energy difference between the two forms in the vapor state is about 4 Kcal/mole. Some of the infrared bands were assigned.

Cristallisation dans I 4 /m avec Z=2; affinement jusqu'a R=0,018. La molecule a la symetrie cristallographique 4/m

Synthese du nouveau coordinat et de son complexe de Rh(I) qui est stable. Etude RX de la structure cristalline

Cationic platinum(II) hydrides [HPtL 2 L′] + (L = phosphines) have been prepared and the ligand steric effects studied; the crystal and molecular structure of trans -[PtH(PCy 3 ) 2 PPh 3 ] PF 6 is described.

Die in MeOH bei 35°C durchgefuhrte Titeloxidation, in der das koordinierte Thiolat nucleophil angreift, liefert den Komplex (Ia), der mit Z=4 in der RG P21/c kristallisiert.

Cristallisation dans I 4 /m avec Z=2; affinement jusqu'a R=0,018. La molecule a la symetrie cristallographique 4/m

The crystal structure of a bidentate hydridotris(pyrazol-1-yl)borate complex with platinum(II) is reported.

A new 11-methylated prostaglandin analogue bearing the unusual 13,14-didehydro-15-oxo bottom side-chain has been prepared by total synthesis. Its complete structure has been established unambiguously by a single crystal X-ray analysis.