Biomedical subjects

W R Chang

Publications and source records attributed to W R Chang.

29 records · Page 2Linked to original sources

PubMed1996

Crystal structure of R-phycoerythrin from Polysiphonia urceolata at 2.8 A resolution.

The structure of R-phycoerythrin (R-PE) from Polysiphonia urceolata was determined at 2.8 A resolution. The crystals belong to space group R3 with unit cell dimensions of a = b = 189.8 A, c = 60.1 A. The subunit composition of R-PE is (alpha 2 beta 2)3 gamma. The three-dimensional structure of R-PE was solved by the multiple isomorphous replacement method. After several cycles of model building and refinement, the crystallographic R-factor of the final model is 18.0% with data from 10.0 to 2.8 A resolution. The four phycoerythrobilin chromophores alpha 84, alpha 140a, beta 84 and beta 155 in an (alpha beta) unit are each covalently bound to a cysteine residue through ring A. The phycourobilin chromophore is bound to cysteine beta 50 by ring A and bound to cysteine beta 61 by ring D. The ring A and ring D of phycourobilin deviate from the conjugate plane formed by ring B and ring C and the four rings form a boat-shaped structure. R-PE contains a 34 kDa gamma subunit that is assumed to lie in the central channel of the molecular disc (alpha 2 beta 2)3. The energy transfer and relationship between cysteine residues and chromophores are discussed.

Bacterial Proteins↗

PubMed1996

Purification and crystal growth of F1-ATPase from pig heart mitochondria.

A method has been evolved toward the aim of getting suitable crystals for high resolution of structural analysis of F1-ATPase by X-ray crystallography. The different conditions for crystal growth of ATPase that were isolated and purified by different methods from pig heart mitochondrial ATP synthase had been compared and screened. A simple method for purification of F1-ATPase was adopted. The F1-ATPase is released with chloroform from submitochondrial particles. Then it was treated with fractional precipitation of (NH4)2SO4 and finally was further purified by employing the sephadex G 200 column. The crystals of F1-ATPase were usually obtained after a few months. They appeared to have uniform morphology of tetrahedron. They diffracted to a resolution of 7A. The diffraction data were collected on the XRD-100 Siemens Area Detector. According to a total of 240 frames, the cell parameters obtained are a = b = 147 A, c = 208 A, alpha = beta = gamma = 90 alpha, the probable space group is P4 or its antipode. The reproducibility of this method for crystallization of F1-ATPase is good.

Animals↗

PubMed1994

A proposed interaction model of the insulin molecule with its receptor.

Based on the extensive structural comparisons among the determined structures of the different species and crystal forms of insulin and its derivatives in our laboratory, it was suggested that the binding interaction with the receptor molecule should take place mainly on an amphipathic surface of the insulin molecule. In the middle of this amphipathis surface, there was a hydrophobic surface with an area of about 150 A2, while the polar and charged groups distributing around the hydrophobic surface constructed a hydrophilic zone. The hydrophobic surface was usually covered by the extended B-chain C-terminal peptides with great mobility. The angle between the proposed binding interaction surface and the surface of dimerization was about 20 degrees. The results from studies on structures of A1-(L-Trp) insulin and A1-(D-Trp) insulin confirmed the interaction mechanism model we proposed.

Amino Acid Sequence↗

PubMed1993

Studies on long-acting insulin: crystal structure of Arg-B31 human insulin at 2.0A resolution.

The crystal structure of Arg-B31 human insulin (ABHI), a long-acting insulin derivative, has been determined at 2.0 A resolution by using X-ray diffraction analysis. The final crystallographic R factor of the structure model after the refinement is 0.189 with the bond length r. m. s deviation of 0.018 A. The refined structure of ABHI showed that the conformation of B-chain C-terminal residues was more stable than that in the native molecule. A striking structural feature of ABHI was an additional ion pair formed between Arg-B31 of molecule I and Glu-B21 of molecule II in a dimer, and three ionic bonds between the neighbouring molecules thereby appeared on the surface of ABHI hexamer. These secondary bonds generated by the insertion of the residue Arg-B31 should make the rate of dissociation of ABHI hexamer slow down when it was injected into the body and the property of protraction should be produced by a 'depot effect'. This ought to be the main structure basis of the prolonged action of ABHI. The results observed here demonstrate that the main idea we used in search for long-acting insulin is reasonable and correct which goes like this: making some additional non-covalent bonds between insulin monomers so as to slow down the dissociation of insulin oligomers and gain the protraction from a 'depot effect', which may be used as a principle in the further research. It also shows an impressive example that the experimental result reported here is in agreement with the theoretical prediction before the structural determination.

Crystallization↗

PubMed1993

Studies on the crystal structure of [L-Met]B0 bovine insulin at 3.0A resolution.

Based on the crystal symmetry of [L-Met]B0 bovine insulin (LMBBI) and the fundamental theory of the molecular packing method, the scheme for the determination of the position and orientation of the molecules by only using one-dimensional rotation and one-dimensional translation was chosen to be used, and therefore the calculation of the rotation function of the molecular replacement method and the refinement of the rotational and translational parameters by using the R-factor search method were simplified greatly. After the preliminary refinement by using the macromolecular rigid body refinement technique, the molecular model was further refined and adjusted by using the energy-minimizing stereochemical-restrained least squares refinement technique assisted by the manual revision on the difference Fourier maps. The L-Met residues on the N-terminus of the B-chain appeared clearly on the final electron density map.

Animals↗

PubMed1992

The characteristics and motion model of insulin monomer.

The extensive conformational comparisons among the determined structures of the different species and crystal forms of insulin and the varied insulin derivatives were performed by using the least-squares superimposition technique and the graphics technique. The results of the investigation showed that the structure of molecule I in 2Zn insulin was closer to that of the natural monomer; the conformational difference between two molecules of a dimer came out during dimerization and it was further improved and stabilized during the hexamerization and packing of hexamers in crystal; through the hinge peptides, such as A10, B4, B8, B24, B20 and B23, there was a flexible relative motion among the structural segments in the insulin molecule, and the residues at the B-chain C-terminal might have a shift of more than 10A; the mobility for each residue side-chain was very different due to the different surroundings.

Insulin↗

PubMed1992

The possible mechanism of binding interaction of insulin molecule with its receptor.

Detailed structural comparisons and investigation of DPI, 2 Zn insulin and some other derivatives of insulin were performed by the least-squares superimposition technique and the graphics technique. It is pointed out in this paper that the binding interaction with the receptor molecule should take place mainly on an amphipathic surface of the insulin molecule. In the middle, there is a hydrophobic surface with an area of about 150 A2 consisting of many hydrophobic residues; while the polar or charged groups distributing around the hydrophobic surface construct a hydrophilic zone. The hydrophobic surface is usually covered by the extended B-chain C-terminal peptides with great mobility and protected from the solvent molecules. The angle between the amphipathic surface and the surface of dimerization is about 20 degrees. The results from the detailed structural comparison between Al-(L-Trp) insulin and Al-(D-Trp) insulin have provided a very good explanation to their great difference in biological activity, and confirmed our proposed binding interaction model of the insulin molecule with its receptor as well.

Animals↗

PubMed1991

Crystal structure of a bovine neurophysin II dipeptide complex at 2.8 A determined from the single-wavelength anomalous scattering signal of an incorporated iodine atom.

The crystal structure of a dipeptide complex of bovine neurophysin II has been solved at 2.8 A resolution solely by using single-wavelength anomalous scattering data from a single iodinated derivative. The asymmetric unit is an elongated tetramer of dimensions 110 x 40 x 30 A, composed of two dimers related by pseudo twofold symmetry. Each monomer consists of two homologous layers, each with four antiparallel beta-strands. The two regions are connected by a helix followed by a long loop. Monomer-monomer contacts involve antiparallel beta-sheet interactions, which form a dimer with two layers of eight beta-strands. One peptide per monomer occupies the principal hormone-binding pocket formed by part of the amino-terminal region and parts of the connecting helix and loop, with binding to protein consistent with conclusions drawn from solution studies. Dimer-dimer contacts involve the Tyr49 region adjacent to this site. A fifth dipeptide, of unknown biological significance, helps to stabilize one of the monomer-monomer interfaces and the tetramer-tetramer network in the crystal.

Amino Acid Sequence↗

PubMed1989

A new crystal form of ricin-OR.

Ricin-OR, an antitumor toxin, has been crystallized in space group P2 with cell parameters a = 8.77 nm, b = 4.64 nm, c = 7.64 nm and beta = 101 degrees. There is one molecule in the asymmetric unit and the solvent content is estimated to be 48% by volume. The crystals diffract to 0.25 nm resolution which is higher than that of the previously reported C2 crystal form which had a solvent content of 65%.

Antineoplastic Agents↗

PubMed1989

Crystal structure determination of desheptapeptide (B24--B30)-insulin.

Desheptapeptide (B24--B30)-insulin (DHPI), an essentially inactive insulin analog, is crystallized in space group P212121 with two molecules in an asymmetric unit. The orientations of the molecules in the crystal cell have been determined by using Patterson search method at 6 A resolution and the positions of the molecules are deduced from translation function calculation and R search at 3 A resolution. After using the rigid body refinement (CORELS) further to refine the orientational and positional parameters as well as the initial energy restrained refinement (EREF) for the model, the crystallographic R value is reduced to 0.384 at 3 A resolution. The initial Fourier map shows that the B-chain N-terminal (B1-B8) and C-terminal (B20-B22) segments, compared with the native 2 zinc insulin, exhibit drastic conformational changes, but the three helices of B- and A-chains and their relative arrangement are essentially kept in DHPI.

Crystallography↗

PubMed1984

The microbial production of amylase inhibitor and its application. I. Isolation and cultivation of Streptomyces nigrifaciens NTU-3314.

In the course of screening amylase inhibitor producing, microorganisms, a strain identified as Streptomyces nigrifaciens NTU-3314 was found to have the highest inhibitor-producing ability among the other isolated strains. This strain was aerobically cultured at 30 degrees C in a 5l jar fermentor with a working volume of 2l. The optimum cultural medium consisted of defatted soybean flake 3.0%, potato starch 4.0%, casein 0.6%, sucrose 0.6%, serine 0.02% and NaCl 0.8% (pH 7.0). With an aeration rate of 1.5 vvm, an agitation speed of 300 rpm and an inoculum of 15% seed (previously grown in seed medium 3), the highest amount of inhibitor was obtained after 24 hours of cultivation. The amylase inhibitor produced had inhibitory effects on both alpha-amylase and glucoamylase, but not on beta-amylase, alpha-glucosidase, beta-glucosidase or dextranase. It was quite stable in 0.1M phosphate buffer (pH 7.0) and nearly 100% of its activity was retained even after boiling at 100 degrees C for 20 min.

Amylases↗