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Biomedical subjects

Y Guan

Publications and source records attributed to Y Guan.

At least 163 records · Page 9Linked to original sources
PubMed1996

Vibrational analysis of nucleic acids. IV. Normal modes of the DNA phosphodiester structure modeled by diethyl phosphate.

Raman and ir spectra are reported for diethyl phosphate [(CH3CH2O)2PO2-] and diethyl phosphate isotopomers incorporating carbon-13 at methylene group sites [(CH313CH2O)2PO2-] and deuterium substituents on methyl and methylene carbons [(CH3CD2O)2PO2-, (CD3CH2O)2PO2-, (CD3CD2O)2PO2-]. The vibrational spectra are analyzed to develop a consistent set of assignments for the C-C-O-P(O2-)-O-C-C network, which serves as a model for the nucleic acid phosphodiester backbone. The present study resolves previously conflicting vibrational assignments for the phosphodiester skeleton and provides a firm empirical basis for interpreting conformationally sensitive modes of DNA and RNA. Ab initio vibrational analyses have also been conducted on the above isotopomers of diethyl phosphate in the trans-gauche-gauche-trans conformation, optimized using the 3-21+G* basis set at the restricted Hartree-Fock level. The ab initio calculations are in good agreement with the empirical results, thus strengthening the proposed assignment scheme for Raman and infrared spectra. The present study provides a basis for improvement of empirical force fields utilized in previous normal coordinate analyses of the nucleic acid phosphodiester group.

DNA↗
PubMed1996

[Study of an ancient corpse of the Warring States period unearthed from Tomb No. 1 at Guo-Jia Gang in Jingmen City (A comprehensive study)].

An ancient female corpse excavated from the robbed tomb No. 1 at Guo-Jia-Gang in Jingmen city of Hubei Province was studied. It was confirmed that the corpse was buried more than 2,300 years ago, namely at the middle stage of the Warring States period and is the earliest one of the ancient coffin corpses unearthed in China so far. It is of the same type as the ancient corpses of Weatern Han Dynasty excavated from tomb No. 1 at Ma-Wang-Dui in Changsha City and from the tomb No. 168 at Phoenix Hill in Jinagling City respectively. The collagenous fibers of connective tissue from all parts in the corpse were well preserved, showing fine ultrastructure with clear periodical cross banding, and a lot of bacterial spores were found between them. In addition, a large number of eggs of clonorchis sinensis and trichuris trichiura were found in the content of the bowel. The level and the cause of good preservation were discussed and it was believed that the good preservation may result from the combined effect of the internal and external environmental factors around the corpse.

Animals↗
PubMed1996

Vibrational analysis of nucleic acids. V. Force field and conformation-dependent modes of the phosphodiester backbone modeled by diethyl phosphate.

A generalized valence force field is derived for the diethyl phosphate anion [(CH3CH2O)2PO2-] and its deuterium [(CH3CD2O)2PO2-, (CD3CH2O)2PO2- and (CD3CD2O)2PO2-] and carbon-13 [(CH3 13CH2O)2PO2-] derivatives in the stable trans-gauche-gauche-trans conformation. Normal coordinate analysis of the trans-gauche-gauche-trans conformer, which serves as a structural analog of the nucleic acid phosphodiester group, is based on comprehensive infrared and Raman spectroscopic data and vibrational assignments obtained for the diethyl phosphate anion. The generalized valence force field is in good agreement with the scaled ab initio force field of diethyl phosphate and represents significant improvement over earlier modeling of the phosphodiester moiety with dimethyl phosphate. The conformational dependence of skeletal C-C-O-P(O2-)-O-C-C stretching vibrations is also explored. Starting with the trans-gauche-gauche-trans conformation, the frequency dependence of skeletal stretching modes has been obtained by stepwise rotation of the torsion angles of the P-O and C-O bonds corresponding to nucleic acid torsions alpha (P-O5'), beta (O5'-C5'), epsilon (C3'-O3'), and zeta (O3'-P). Both symmetric and antisymmetric phosphoester stretching modes are highly sensitive to P-O and C-O torsions, whereas symmetric and antisymmetric phosphodioxy (PO2-) stretching modes are less sensitive. The present results provide an improved structural basis for understanding previously developed empirical correlations between vibrational marker bands and nucleic acid backbone conformation.

Models, Chemical↗
PubMed1996

Emergence of avian H1N1 influenza viruses in pigs in China.

Avian influenza A viruses from Asia are recognized as the source of genes that reassorted with human viral genes to generate the Asian/57 (H2N2) and Hong Kong/68 (H3N2) pandemic strains earlier in this century. Here we report the genetic analysis of avian influenza A H1N1 viruses recently isolated from pigs in southern China, a host suspected to generate new pandemic strains through gene reassortment events. Each of the eight gene segments was of avian origin. Phylogenetic analysis indicates that these genes form an Asian sublineage of the Eurasian avian lineage, suggesting that these viruses are an independent introduction into pigs in Asia. The presence of avian influenza viruses in pigs in China places them in an optimal position for transmission to humans and may serve as an early warning of the emergence of the next human influenza virus pandemic.

Animals↗
PubMed1996

Drosophila rosA gene, which when mutant causes aberrant photoreceptor oscillation, encodes a novel neurotransmitter transporter homologue.

The Drosophila receptor oscillation A (rosA) mutations, which cause electroretinogram (ERG) defects, including oscillations, were localized to the 24F4-25A2 region of chromosome 2L. Genomic fragments from this region, isolated from bacteriophage P1 clones, included those that detect transcriptional defects in rosA mutants in RNA blot experiments. One of these genomic fragments was used to screen a head cDNA library. The largest cDNA clone (3.6 kb) isolated was shown to rescue a rosA mutant in P element-germline transformation experiments. The ROSA protein deduced from the open reading frame in the 3.6 kb rosA cDNA is 943 amino acids long and is 36-41% identical to members of the superfamily of Na+/Cl(-)-dependent neurotransmitter transporters, with no indication of higher sequence identity to any one subgroup within the superfamily. RNA blot experiments revealed multiple transcripts in various developmental stages, the most abundant one being a 3.7 kb transcript, particularly in the adult head. Tissue in situ experiments identified the rosA transcript to be localized to many tissues, with higher levels of hybridization in the nervous system and digestive tract. The results demonstrate that the rosA gene encodes a novel Na+/Cl(-)-dependent transporter important for normal response properties of the photoreceptor.

Amino Acid Sequence↗
PubMed1995

Primary familial polycythemia: a frameshift mutation in the erythropoietin receptor gene and increased sensitivity of erythroid progenitors to erythropoietin.

Primary familial and congenital polycythemia (PFCP) is characterized by erythrocytosis with normal arterial PO2, blood P50, and serum erythropoietin (EPO) levels. In two PFCP families EPO receptor (EPOR) polymorphisms cosegregated with PFCP. A heterozygous insertion of G at EPOR nucleotide 5975 was identified in genomic DNA from polycythemic members of family no. 2. 5974insG shifts the reading frame at codon 430, predicting amino acid substitutions and truncation of the last 64 amino acids. Wild-type and mutant EPOR transcripts were detected in erythroid progenitors from affected individuals. Burst-forming units-erythroid from patients exhibited increased colony size and sensitivity to EPO. Transfected Ba/F3 cells expressing EPOR 5974insG exhibited increased EPO sensitivity compared with cells expressing wild-type EPOR. The functional effect of this EPOR mutation was directly compared with the other C-terminal mutations reported in unrelated PFCP families by expression in Ba/F3 cells. The transfected cells with another primary polycythemia associated EPOR mutant construct (G6002A) also exhibited increased sensitivity to EPO.

Adult↗
PubMed1995

Cloning and characterization of a dihydrolipoamide acetyltransferase (E2) subunit of the pyruvate dehydrogenase complex from Arabidopsis thaliana.

A cDNA encoding a dihydrolipoamide acetyltransferase (E2) subunit of the pyruvate dehydrogenase complex has been isolated from Arabidopsis thaliana. A cell culture cDNA expression library was screened with a monoclonal antibody (JIM 63) raised against nuclear matrix proteins, and four clones were isolated. One of these was 2175 base pairs in length, and it contained an open reading frame with an amino acid sequence and domain structure with strong similarity to the E2s of other eukaryotic and prokaryotic organisms. The organization and number of functional domains within the Arabidopsis protein are identical to those of the human E2, although the amino acid sequences within these domains are equally similar to those of the yeast and human proteins. The predicted amino acid sequence reveals the presence of a putative amino-terminal leader sequence with characteristics similar to those of other proteins, which are targeted to the plant mitochondrial matrix. The cross-reactivities of plant mitochondrial matrix proteins with JIM 63 and antibodies raised against the E2 and protein X components of eukaryotic pyruvate dehydrogenase complexes are consistent with the clone encoding a mitochondrial form of E2 and not the smaller protein X. The E2 mRNA of 2.2 kilobases was expressed in a range of Arabidopsis and Brassica napus tissues.

Acetyltransferases↗
PubMed1995

Electrostatic potential distribution of the gene V protein from Ff phage facilitates cooperative DNA binding: a model of the GVP-ssDNA complex.

The crystal structure of the gene V protein (GVP) from the Ff filamentous phages (M13, fl, fd) has been solved for the wild-type and two mutant (Y41F and Y41H) proteins at high resolution. The Y41H mutant crystal structure revealed crystal packing interactions, which suggested a plausible scheme for constructing the polymeric protein shell of the GVP-single-stranded DNA (ssDNA) complex (Guan Y, et al., 1994, Biochemistry 33:7768-7778). The electrostatic potentials of the isolated and the cooperatively formed protein shell have been calculated using the program GRASP and they revealed a highly asymmetric pattern of the electrostatic charge distribution. The inner surface of the putative DNA-binding channel is positively charged, whereas the opposite outer surface is nearly neutral. The electrostatic calculation further demonstrated that the formation of the helical protein shell enhanced the asymmetry of the electrostatic distribution. A model of the GVP-ssDNA complex with the n = 4 DNA-binding mode could be built with only minor conformational perturbation to the GVP protein shell. The model is consistent with existing biochemical and biophysical data and provides clues to the properties of GVP, including the high cooperatively of the protein binding to ssDNA. The two antiparallel ssDNA strands form a helical ribbon with the sugar-phosphate backbones at the middle and the bases pointing away from each other. The bases are stacked and the Phe 73 residue is intercalated between two bases. The optimum binding to a tetranucleotide unit requires the participation of four GVP dimers, which may explain the cooperativity of the GVP binding to DNA.

Amino Acid Sequence↗
PubMed1995

Yishou jiangzhi (de-blood-lipid) tablets in the treatment of hyperlipemia.

The Yishoujiangzhi (de-blood-lipid) tablets (composed of Radix Polygori Multiflori, Rhizoma Polygonati, Fructus Lycii, Crataegus Pinnatifida and Cassia Tora) were used in the treatment of 130 cases of hyperlipemia, achieving an effective rate of 87.0% in lowering serum cholesterol and 80.8% in lowering triglyceride.

Adult↗
PubMed1995

[Correction of the secondary nasal deformity in bilateral cleft lip with a new technique].

Bilateral cleft lip often has nasal deformities of various degrees. It is not enough to elongate the nasal columella for such deformities. Based on the thoughts that secondary deformities of the nose and lip should be treated as a whole, the authors introduced a new technique, in which five aspects of the deformities were considered and treated at the same time. Thirteen patients have undergone surgical correction with satisfactory results.

Abnormalities, Multiple↗
PubMed1995

[Correction of unilateral cleft lip nasal deformity with modified Bardach's technique].

Twenty-nine cases of unilateral cleft lip nasal deformities were corrected with modified Bardach's technique. Overall results were satisfactory. The key to a successful and stable correction of the nasal deformity is to lengthen the columella on the cleft side and to mobilize alar cartilage from its surrounding tissue, creating a symmetric shape and length. The major advantages of the technique are lengthening of the cleft columella and creation of a symmetric and well-projected nasal tip. The surgical technique is described in details. Some considerations before and during operation were discussed.

Adolescent↗
PubMed1994

Crystal structures of Y41H and Y41F mutants of gene V protein from Ff phage suggest possible protein-protein interactions in the GVP-ssDNA complex.

Gene V protein (GVP) encoded by the filamentous phage Ff (M13, fl, fd) is a homodimeric protein of 87 amino acids that binds to single-stranded DNA (ssDNA) nonspecifically and cooperatively. The structure (monoclinic C2 form) of the wild-type protein has been determined and refined at 1.8-A resolution [Skinner et al. (1994) Proc. Natl. Acad. Sci. U.S.A. 91, 2071-2075]. The monomer structure consists of a somewhat distorted five-stranded beta-barrel core with three prominent loops: a DNA-binding loop, a dyad loop, and a dimer contact loop. The amino acid residue at position 41 plays an important role in the dimer-dimer interactions of the protein-ssDNA complex. Two Y41 mutant structures have been studied by X-ray crystallography. The Y41F GVP structure has been refined to an R-factor of 0.180 at 2.2-A resolution and is very similar to the wild-type (wt) structure (rmsd of all C alpha atoms = 0.30 A). In contrast, Y41H GVP forms a new crystal lattice in the space group P2(1)2(1)2(1) with a = 77.18 A, b = 84.17 A, and c = 28.62 A. Its structure has been solved by the molecular replacement method and refined to an R-factor of 0.170 at 2.5-A resolution. The two monomers of Y41H are crystallographically independent, and their structures remain similar to wt-GVP but with significant differences, particularly in the DNA-binding hairpin region. In both crystals, the loop (residues 36-43) that contains the Y41 residue is involved in the crystal dimer packings but in a different manner. The dimer-dimer contacts found in the wt-GVP crystal may be important for GVP aggregation in the absence of DNA. In the presence of DNA, the dimer-dimer contacts may switch to the type found in the Y41H crystal, allowing the GVP-ssDNA complex to form cooperatively. A model of the complex, consistent with existing biochemical and biophysical data, has been constructed from those crystal packing data.

Amino Acid Sequence↗
PubMed1994

Structure of the gene V protein of bacteriophage f1 determined by multiwavelength x-ray diffraction on the selenomethionyl protein.

The crystal structure of the dimeric gene V protein of bacteriophage f1 was determined using multiwavelength anomalous diffraction on the selenomethionine-containing wild-type and isoleucine-47-->methionine mutant proteins with x-ray diffraction data phased to 2.5 A resolution. The structure of the wild-type protein has been refined to an R factor of 19.2% using native data to 1.8 A resolution. The structure of the gene V protein was used to obtain a model for the protein portion of the gene V protein-single-stranded DNA complex.

Crystallography, X-Ray↗
PubMed1994

Vibrational analysis of nucleic acids. I. The phosphodiester group in dimethyl phosphate model compounds: (CH3O)2PO2-, (CD3O)2PO2-, and (13CH3O)2PO2-.

Normal coordinate analyses and vibrational assignments are presented for the dimethyl phosphate anion [(CH3O)2PO2-] and its deuteriomethyl [(CD3O)2PO2-] and carbon-13 [(13CH3O)2PO2-] derivatives in the gauche-gauche conformation. The dimethyl phosphate anion, which is the simplest model for the nucleic acid phosphodiester moiety, exhibits many of the spectral complexities of DNA and RNA and has previously resisted a complete and consistent vibrational analysis. In the present study we make use of new experimental data on the dimethyl phosphate isotopomers, including Raman depolarization measurements, to develop a consistent valence force field for normal modes of the C--O--P--O--C phosphodiester network and its hydrogenic substituents, as well as for stretching and bending modes of the O--P--O network of the anionic phosphodioxy group (PO2-). The force field established for dimethyl phosphate incorporates one significant nonbonded force constant, introduced from ab initio calculations, to account for interaction between the two ester C--O bonds. This study resolves previous problematic assignments for conformation-sensitive symmetric (in-phase) and asymmetric (out-of-phase) skeletal stretching modes of the ester linkages and demonstrates substantial anharmonicity in the hydrogen-stretching vibrations of the methyl substituents. New assignments are proposed for Raman bands of the phosphodioxy group, which may serve as potential indicators of structure and interaction of the DNA phosphates.

Carbon Isotopes↗
PubMed1994

E. coli penicillin acylase isolation by selective release, aqueous two-phase partitioning and ultrafiltration.

A procedure has been developed for the purification of penicillin acylase from E. coli fermentation broths. The method described is based primarily on selective release from biomass, charge-directed partitioning in an aqueous two-phase system, and the use of ultrafiltration membranes to recycle the modified polyethylene glycol required and to further purify the enzyme. Each step has been discussed and comparisons have been made with other approaches, where possible. Suggestions have been made for optimisation in process engineering. The approach developed may be applicable to other beta-lactam antibiotic acylases or more generally to some of the other E. coli periplasmic proteins.

Biological Assay↗
PubMed1993

Protective effects of silybin and tetrandrine on the outcome of spontaneously hypertensive rats subjected to acute coronary artery occlusion.

The effects of silybin and tetrandrine on the survival of spontaneously hypertensive rats subjected to acute coronary artery occlusion were investigated. The mortality after acute coronary occlusion in spontaneously hypertensive rats (66.7%) was higher than that of control Wistar-Kyoto rats (20%, P < 0.05). Oral administration of silybin (300 mg/kg daily) for 8-12 days reduced mortality in spontaneously hypertensive rats (0, P < 0.01 in comparison with untreated spontaneously hypertensive rats). Administration of tetrandrine 40 mg/kg daily for 8-12 days reduced the mortality to some extent (22.2%, P = 0.051, as compared with control rats). Silybin reduced blood pressure and the incidence of post-occlusion arrhythmias in spontaneously hypertensive rats to the same extent as tetrandrine. Both silybin and tetrandrine decreased the severity of ventricular hypertrophy. Although there were significant decreases in risk zone and infarct zone in silybin- and tetrandrine-treated rats, the ratio of infarct to risk zone was not changed. The results implies that silybin may be beneficial when used in hypertensive patients who develop acute myocardial infarction.

Alkaloids↗
PubMed1993

Molecular structure of cyclic diguanylic acid at 1 A resolution of two crystal forms: self-association, interactions with metal ion/planar dyes and modeling studies.

Cyclic ribodiguanylic acid, c-(GpGp), is the endogenous effector regulator of cellulose synthase. Its three dimensional structure from two different crystal forms (tetragonal and trigonal) has been determined by x-ray diffraction analysis at 1 A resolution. Both structures were solved by direct methods and refined by block-matrix least squares refinement to R-factors of 0.112 (tetragonal) and 0.119 (trigonal). In both crystal forms, two independent c-(GpGp) molecules associate with each other to form a self-intercalated dimer. All four c-(GpGp) molecules have very similar backbone conformation. The riboses are in the C3'-endo pucker with pseudorotation angles ranging from -7.2 degrees to 16.5 degrees and the bases have anti glycosyl chi angles (-175.5 degrees to 179.7 degrees). In the tetragonal form, a hydrated cobalt ion is found to coordinate to two N7 atoms of adjacent guanines, forcing these two guanines to destack with a large dihedral angle (33 degrees). This metal coordination mechanism has been noted previously in other Pt- or Co-GMP complexes and may be relevant to the binding of the anticancer drug cisplatin to a GpG sequence in DNA. A model of the adduct between cisplatin and a d(CAATGGATTG) duplex has been constructed in which the induced bending of the DNA helix at the Pt crosslinking site is 33 degrees, consistent with earlier electrophoretic analyses. Moreover, c-(GpGp) exhibits unusual spectral properties not seen in other cyclic dinucleotides. It interacts with planar organic intercalator molecules in ways similar to double helical DNA. We propose a cage-like model consisting of a tetrameric c-(GpGp) aggregate in which a large cavity (host molecule) is generated to afford a binding site for certain planar intercalators (guests molecules). The aggregate likely uses a hydrogen bonding scheme the same as that found in the G-quartet molecules, e.g., telomere DNA. The conformation of c-(GpGp) also suggests that certain nearest-neighbor intercalators may be synthesized on the basis of its unique molecular framework. Modeling studies have been carried out to test this hypothesis.

Base Sequence↗