Studies on the crystal structure of (D-Ala)-B0 porcine insulin at 1.9 A resolution

The crystal structure of (D-Ala)-B0 porcine insulin has been determined, using data to 1.9 A and atomic parameters of 2 Zn porcine insulin as a starting model, and through the use of the difference method and the restrained least square method, to a final R-factor of 0.211 and r.m.s. deviation of 0.057 A for the bond lengths. The electron densities of B0 residues were very clear. Introduction of B0 residues into the molecules had reduced the thermal vibration of the N-terminus of B-chain for both molecules I and II and made the molecules pack closer in the crystal. The obvious differences between the crystal structures of 2 Zn and (D-Ala)-B0 porcine insulin were the conformations of partial polar groups around the possible receptor binding surface and the assembly mode of two helixes of A-chain in molecule I. In the local environment of the N-terminus of B-chain there were great differences between the crystal structures of (D-Ala)-B0 porcine insulin, (Trp)-B1 porcine insulin and Des B1(Phe) bovine insulin. In this paper the structure-immunoactivity relationships of insulin molecule have also been discussed briefly.     

The crystal structure of silver carp insulin at medium resolution

It is an important way of surveying the structure-function relationship of insulin to study insulins from different species. Based on the structure model of an orthorhombic crystal obtained by the molecular replacement method, the crystallographic refinement of a hexamer of silver carp insulin in an asymmetric unit has been carried out with 2.8 A resolution data using the restrained least-squares method. The comparisons of insulin structures have shown that the six silver carp insulin molecules have very similar but not identical three-dimensional structures which are similar to the known 2 Zn pig insulin structure but remarkably different in some local conformations.     

Crystal structure determination of 4-zinc bovine insulin at 1.9 A resolution

With the isomorphous difference Fourier method and the restrained least-squares refinement technique, the crystal structure of 4-zinc bovine insulin in space group R3 was determined. The final crystallographic residual is 0.19 at 1.9 A resolution. Based on the refined model, the structural mechanism for prolonged action of 4-zinc insulin is discussed.     

Structure of bistramide A-actin complex at a 1.35 angstroms resolution

Bistramide A is a highly potent antiproliferative marine natural product from Lissoclinum bistratum. We have previously established actin as the primary cellular receptor of bistramide A. We report herein the X-ray structure of bistramide A bound to monomeric actin at a resolution of 1.35 A. The most notable aspect of the bistramide A-actin structure is an extensive hydrogen-bonding network established upon a deep penetration of the central segment of bistramide A into the actin-binding cleft between subdomains 1 and 3. The structure presents the first insight into the observed ability of bistramide A to modulate G-actin polymerization. The structural information combined with our ability to chemically modify the bistramide framework provides the basis for rational development of a series of new synthetic analogues as useful probes for studying actin cytoskeleton and as potential therapeutic leads.     

The 2.0 angstroms crystal structure of a pocilloporin at pH 3.5: the structural basis for the linkage between color transition and halide binding

The pocilloporin Rtms5 and an engineered variant Rtms5H146S undergo distinct color transitions (from blue to red to yellow to colorless) in a pH-dependent manner. pK(a) values of 4.1 and 3.2 were determined for the blue (absorption lambda(max), 590 nm) to yellow (absorption lambda(max), approximately 453 nm) transitions of Rtms5 and Rtms5H146. The pK(a) for the blue-yellow transition of Rtms5H146S increased by 1.4 U in the presence of 0.1 M KI, whereas the pK(a) for the same transition of Rtms5 was relatively insensitive to added halides. To understand the structural basis for these observations, we have determined to 2.0 angstroms resolution the crystal structure of a yellow form of Rtms5H146S at pH 3.5 in the presence of iodide. Iodide was found occupying a pocket in the structure with a pH of 3.5, forming van der Waals contacts with the tyrosyl moiety of the chromophore. Elsewhere, it was determined that this pocket is occupied by a water molecule in the Rtms5H146S structure (pH 8.0) and by the side chain of histidine 146 in the wild-type Rtms5 structure. Collectively, our data provide an explanation for the observed linkage between color transitions for Rtms5H146S and binding to halides.     

The crystal structure of LSbOF

LSbOF is orthorhombic, space group Pnma, with a = 8.873, b = 4.099 and c = 5.483 Å. Four anions are bonded to Sb³⁺, all to one side, and such polyhedra form chains by edge sharing along c. Evidence is given for an ordered arrangement of fluorine and oxygen anions. The lone pair of electrons is described as taking a certain volume, the centre of which is derived. Relationships with other structures are discussed.     

The crystal structure of 1-p-bromophenylsilatrane at 293 K and 133 K

The crystal structure of 1-p-bromophenylsilatrane was determined at ambient and low temperature. The methylene groups of the silatrane skeleton in the β-position to the nitrogen atom are disordered in the ambient temperature structure. The disorder disappears at 133 K. The Si ← N dative bond length is nearly identical at both temperatures (2.139(3) and 2.132(2) Å). The deviation of the atoms in the silatrane moiety from the ideal three-fold symmetry seems to point to the most dynamically behaving parts of the molecule.     

The crystal structure of the molybdenum boride Mo1−xB3

The structure of Mo_1?xB₃, with x close to 0.20, has been investigated using powder diffractometry, in conjunction with the electron microprobe and chemical analysis. The range of homogeneity of the compound is very small and does not include the stoichiometric composition. The structure is described in the hexagonal space group $\text{P6}{}_3\text{mmc}$ with the axes a = 5.2026 (2) Å and c = 6.3489 (3) Å. No significant variations in cell dimensions were observed. There are four formula units per unit cell with molybdenum at 2(b) (occupancy 60%) and 2(c) and boron at 12(i) with x = 0.333. The refinement was performed with least-squares and Fourier difference techniques. The final R value, based on intensities, was 8.8%.The structure may be described as a stacking of two-dimensional boron nets and highly defect metal layers. The molybdenum-boron distance exceeds the radius sum by 3%, while the Mo-Mo distances are 7 and 13% longer than the radius sum. There are holes in the structure, which are large enough to accommodate boron atoms. However, there is no evidence that these holes are even partially filled.     

The structure of the singlet tetramethylene diradical intermediate

Ab initio MC SCF geometry optimizations of the gauche and trans conformers of the singlet tetramethylene diradical have been carried out using MC SCF gradients with a minimal (STO-3G) and extended (4-31G) basis set. At both computational levels, it has been found that the tetramethylene diradical exists as a stable species in two different conformations, a gauche and a trans.     

The crystal structure of Rb2SeO4 at high temperature

The crystal structure of Rb₂SeO₄ in its high-temperature phase is reported for the first time. Powder diffraction data collected at T = 898 K show that it is hexagonal (a = 6.3428(1) Å, c = 8.5445(1) Å, V = 297.71(1) Å³, space group P6₃/mmc (194), Z = 2) and is isostructural to Tl₂SeO₄, thus belonging to the α-K₂SO₄ structure type. DSC measurements indicate that the phase transition occurs at T = 818 K.     

The crystal structure of [1.1.1]propellane at 138 K

The molecular structure of [1.1.1]propellane has been determined from single-crystal X-ray diffraction measurements at 138 K. The crystals of this reactive compound were grown from the melt at ca. 263 K. The space group is C2, and the asymmetric unit contains four molecules. All have large thermal motion and two show orientational disorder as well. Because of these problems, the atomic positions cannot be determined with high accuracy. Within the experimental limits, the two ordered molecules have D_3h symmetry, with corrected lengths of central and side bonds of ca. 1.60 Å and 1.53 Å, respectively. At lower temperature, the crystals undergo a phase transition. The transition temperature, in the range of 100 to 132 K, varied from one crystal sample to another. All crystals obtained of the low-temperature phase were twinned, and its space group could not be established.     

The three-dimensional structure of trichosanthin refined at 2.7resolution

The three-dimensional structure of trichosanthin crystallizing in space group C2 has beenrefined at 2.7 resolution from a previously reported starting model at 3 resolution based on asolvent flattened map and the revised primary structure consisting of 247 amlno-acids.The finalR-factor is 19.2% with the root mean-square deviations of 0.018 from ideal bond lengths andof 2.2° from ideal bond angles.Trichosanthin molecule is composed of two domains,the largedomain consisting of 181 amino-acld residues starting from N-terminus and the small domain con-sisting of the rest of the amino-acid residues.The molecule contains eight α-helices,five β-sheetsmade of sixteen β-strands,and some reverse turns.It is noteworthy that some of the α-helicesand β-sheets show irregular hydrogen bonding patterns.Six of the thirteen residues absolutelyconserved in eleven ribosome-inactivating proteins are located in a cleft near the interface ofthe two domains and they are likely to be active sites.Three additional conservative residueslocated in the cleft region might make some functional contribution as well.     

Chemical bonding in the crystal structure of 1-hydrosilatrane

A study has been made of the crystal and molecular structure of 1-hydrosilatrane HSi(OCH_2CH₂)₃N. The quantum chemical calculations of its crystal structure have been carried out. According to an estimate of the energy, the coordination bond N→Si is by 5 kcal mol^?1 stronger than that in the crystal of 1-methylsilatrane. The charge values calculated within the framework of the topological analysis of the electron density demonstrate that the electron density of the coordination bond N→Si is primarily transferred to the region of the equatorial bonds Si—O and, to a lesser extent, to the bond Si—H. On going from the isolated molecule of 1-hydrosilatrane to its crystal, the interatomic distance N—Si decreases, mainly owing to the weak intermolecular interaction C—H...O.