Biomedical subjects

H Y Qi

Publications and source records attributed to H Y Qi.

14 recordsLinked to original sources

PubMed2004

Pectinase production by Aspergillus niger using wastewater in solid state fermentation for eliciting plant disease resistance.

An elicitor of plant disease resistance, pectinase, was produced by solid state fermentation with Aspergillus niger. Sugar beet pulp was used as carbon source and the wastewater from monosodium glutamate production was used as nitrogen and water source. The composition of the fermentation medium was: 11 ml concentrated wastewater (containing NH3-N 38.2 mg/ml), sugar beet pulp 10 g, Na2HPO4.12H2O 0.2 g, KH2PO4 0.04 g in a 500 ml Erlenmeyer flask. The fermentation temperature was 30 degrees C and the relative humidity of the air was 75-90%. The maximum production of pectinase was reached after 96 h cultivation. The crude pectinase extracted from the fermented materials could elicit disease resistance in cucumber and tomato seedlings.

Aspergillus niger↗

PubMed2003

Chromosomal polymorphism of mandarin vole, Microtus mandarinus (Rodentia).

The mitotic and meiotic chromosomes of mandarin vole, Microtus mandarinus Milne-Edwards, from Shandong Province of China were analyzed by conventional, G- and C-banding and Silver-staining techniques. We detected chromosomal polymorphism in the vole, exhibiting diploid chromosome numbers 2n = 48-50 and variable morphology of the 1st pair, one medium sized telocentric pair and the X chromosomes. Four types of karyotypes were revealed in the population. According to banding analysis, there were pericentric inversion, Robertsonian fusion and translocation in M. mandarinus karyotype evolution. The X displayed two different morphologies, which could be explained by prericentric inversion and a telocentric autosome translocation.

Animals↗

PubMed2001

Evidence for a novel GTPase priming step in the SRP protein targeting pathway.

Protein targeting by the signal recognition particle (SRP) pathway requires the interaction of two homologous GTPases that reciprocally regulate each other's GTPase activity, the SRP signal peptide- binding subunit (SRP54) and the SRP receptor alpha-subunit (SRalpha). The GTPase domain of both proteins abuts a unique 'N domain' that appears to facilitate external ligand binding. To examine the relationship between the unusual regulation and unique architecture of the SRP pathway GTPases, we mutated an invariant glycine in Escherichia coli SRP54 and SRalpha orthologs ('Ffh' and 'FtsY', respectively) that resides at the N-GTPase domain interface. A G257A mutation in Ffh produced a lethal phenotype. The mutation did not significantly affect Ffh function, but severely reduced interaction with FtsY. Likewise, mutation of FtsY Gly455 produced growth defects and inhibited interaction with Ffh. The data suggest that Ffh and FtsY interact only in a 'primed' conformation which requires interdomain communication. Based on these results, we propose that the distinctive features of the SRP pathway GTPases evolved to ensure that SRP and the SR engage external ligands before interacting with each other.

Alleles↗

PubMed2001

FtsY binds to the Escherichia coli inner membrane via interactions with phosphatidylethanolamine and membrane proteins.

Targeting of many polytopic proteins to the inner membrane of prokaryotes occurs via an essential signal recognition particle-like pathway. FtsY, the Escherichia coli homolog of the eukaryotic signal recognition particle receptor alpha-subunit, binds to membranes via its amino-terminal AN domain. We demonstrate that FtsY assembles on membranes via interactions with phosphatidylethanolamine and with a trypsin-sensitive component. Both interactions are mediated by the AN domain of FtsY. In the absence of phosphatidylethanolamine, the trypsin-sensitive component is sufficient for binding and function of FtsY in the targeting of membrane proteins. We propose a two-step mechanism for the assembly of FtsY on the membrane similar to that of SecA on the E. coli inner membrane.

Bacterial Proteins↗

PubMed2001

Preparation of levoglucosan by pyrolysis of cellulose and its citric acid fermentation.

Levoglucosan (LG), 1,6-anhydro-beta-D-glucopyranose, was produced by pyrolysis of cellulose. A response surface method was used to optimize the reaction parameters: X1, temperature; X2, time required for heating cellulose from room temperature to the designed pyrolysis temperature; and X3, vacuum, and a Box-Behnken design was employed for this purpose. The optimal temperature and time were found to be 388 degrees C and 26.2 min by fixing the vacuum at 1 mm Hg. The levoglucosan prepared was fermented to citric acid by Aspergillus niger CBX-209, which was a mutant derived by gamma-ray mutagenesis of the parent strain CBX-2. The mutant could produce increasing citric acid with increasing LG purity and had a citric acid yield of 87.5% when using purified levoglucosan as the sole carbon source in a 5 day fermentation period.

Aspergillus niger↗

PubMed1999

SecA is required for the insertion of inner membrane proteins targeted by the Escherichia coli signal recognition particle.

Recent work has demonstrated that the signal recognition particle (SRP) is required for the efficient insertion of many proteins into the Escherichia coli inner membrane (IM). Based on an analogy to eukaryotic SRP, it is likely that bacterial SRP binds to inner membrane proteins (IMPs) co-translationally and then targets them to protein transport channels ("translocons"). Here we present evidence that SecA, which has previously been shown to facilitate the export of proteins targeted in a post-translational fashion, is also required for the membrane insertion of proteins targeted by SRP. The introduction of SecA mutations into strains that have modest SRP deficiencies produced a synthetic lethal effect, suggesting that SecA and SRP might function in the same biochemical pathway. Consistent with this explanation, depletion of SecA by inactivating a temperature-sensitive amber suppressor in a secAam strain completely blocked the membrane insertion of AcrB, a protein that is targeted by SRP. In the absence of substantial SecA, pulse-labeled AcrB was retained in the cytoplasm even after a prolonged chase period and was eventually degraded. Although protein export was also severely impaired by SecA depletion, the observation that more than 20% of the OmpA molecules were translocated properly showed that translocons were still active. Taken together, these results imply that SecA plays a much broader role in the transport of proteins across the E. coli IM than has been previously recognized.

Adenosine Triphosphatases↗

PubMed1999

Ancestral origins and worldwide distribution of the PRNP 200K mutation causing familial Creutzfeldt-Jakob disease.

Creutzfeldt-Jakob disease (CJD) belongs to a group of prion diseases that may be infectious, sporadic, or hereditary. The 200K point mutation in the PRNP gene is the most frequent cause of hereditary CJD, accounting for >70% of families with CJD worldwide. Prevalence of the 200K variant of familial CJD is especially high in Slovakia, Chile, and Italy, and among populations of Libyan and Tunisian Jews. To study ancestral origins of the 200K mutation-associated chromosomes, we selected microsatellite markers flanking the PRNP gene on chromosome 20p12-pter and an intragenic single-nucleotide polymorphism at the PRNP codon 129. Haplotypes were constructed for 62 CJD families originating from 11 world populations. The results show that Libyan, Tunisian, Italian, Chilean, and Spanish families share a major haplotype, suggesting that the 200K mutation may have originated from a single mutational event, perhaps in Spain, and spread to all these populations with Sephardic migrants expelled from Spain in the Middle Ages. Slovakian families and a family of Polish origin show another unique haplotype. The haplotypes in families from Germany, Sicily, Austria, and Japan are different from the Mediterranean or eastern European haplotypes. On the basis of this study, we conclude that founder effect and independent mutational events are responsible for the current geographic distribution of hereditary CJD associated with the 200K mutation.

Amyloid↗

PubMed1997

Roles of histidine-103 and tyrosine-235 in the function of the prolipoprotein diacylglyceryl transferase of Escherichia coli.

Phosphatidylglycerol:prolipoprotein diacylglyceryl transferase (Lgt) is the first enzyme in the posttranslational sequence of reactions resulting in the lipid modification of lipoproteins in bacteria. A previous comparison of the primary sequences of the Lgt enzymes from phylogenetically distant bacterial species revealed several highly conserved amino acid sequences throughout the molecule; the most extensive of these was the region 103HGGLIG108 in the Escherichia coli Lgt (H.-Y. Qi, K. Sankaran, K. Gan, and H. C. Wu, J. Bacteriol. 177:6820-6824, 1995). These studies also revealed that the kinetics of inactivation of E. coli Lgt with diethylpyrocarbonate were consistent with the modification of a single essential histidine or tyrosine residue. The current study was conducted in an attempt to identify this essential amino acid residue in order to further define structure-function relationships in Lgt. Accordingly, all of the histidine residues and seven of the tyrosine residues of E. coli Lgt were altered by site-directed mutagenesis, and the in vitro activities of the altered enzymes, as well the abilities of the respective mutant lgt alleles to complement the temperature-sensitive phenotype of E. coli SK634 defective in Lgt activity, were determined. The data obtained from these studies, in conjunction with additional chemical inactivation studies, support the conclusion that His-103 is essential for Lgt activity. These studies also indicated that Tyr-235 plays an important role in the function of this enzyme. Although other histidine and tyrosine residues were not found to be essential for Lgt activity, alterations of His-196 resulted in a significant reduction of in vitro activity.

Amino Acid Sequence↗

PubMed1995

Mutation in Cys662 of Escherichia coli DNA topoisomerase I confers temperature sensitivity and change in DNA cleavage selectivity.

Cys662 is one of the 12 cysteine residues proposed to be co-ordination sites for binding of three Zn(II) in Escherichia coli DNA topoisomerase I. Oligonucleotide-directed mutagenesis was used to convert Cys662 to either serine or histidine. The mutant enzymes were overexpressed and purified to homogeneity. Analysis of the purified enzymes demonstrated that the mutations resulted in loss of one tightly bound Zn(II). In vivo complementation tests and in vitro relaxation activity assays at different temperatures showed that the partial relaxation activities retained in the two mutant enzymes were temperature sensitive. Fluorescence measurements indicated that the wild-type and mutant enzymes have structural differences. When DNA cleavage specificity was examined, the mutant enzymes were found to have altered cleavage site preferences. The preferred cleavage sites of the wild-type enzyme all had a cytosine residue four nucleotides to the minus side of the break. The cleavage sites produced by the mutant enzymes did not show a preference for cytosine at that position.

Base Sequence↗

PubMed1995

Structure-function relationship of bacterial prolipoprotein diacylglyceryl transferase: functionally significant conserved regions.

The structure-function relationship of bacterial prolipoprotein diacylgyceryl transferase (LGT) Has been investigated by a comparison of the primary structures of this enzyme in phylogenetically distant bacterial species, analysis of the sequences of mutant enzymes, and specific chemical modification of the Escherichia coli enzyme. A clone containing the gene for LGT, lgt, of the gram-positive species Staphylococcus aureus was isolated by complementation of the temperature-sensitive lgt mutant of E. coli (strain SK634) defective in LGT activity. In vivo and in vitro assays for prolipoprotein diacylglyceryl modification activity indicated that the complementing clone restored the prolipoprotein modification activity in the mutant strain. Sequence determination of the insert DNA revealed an open reading frame of 837 bp encoding a protein of 279 amino acids with a calculated molecular mass of 31.6 kDa. S. aureus LGT showed 24% identity and 47% similarity with E. coli, Salmonella typhimurium, and Haemophilus influenzae LGT.S. aureus LGT, while 12 amino acids shorter than the E. coli enzyme, had a hydropathic profile and a predicted pI (10.4) similar to those of the E. coli enzyme. Multiple sequence alignment among E. coli, S. typhimurium, H. influenzae, and S. aureus LGT proteins revealed regions of highly conserved amino acid sequences throughout the molecule. Three independent lgt mutant alleles from E. coli SK634, SK635, and SK636 and one lgt allele from S. typhimurium SE5221, all defective in LGT activity at the nonpermissive temperature, were cloned by PCR and sequenced. The mutant alleles were found to contain a single base alteration resulting in the substitution of a conserved amino acid. The longest set of identical amino acids without any gap was H-103-GGLIG-108 in LGT from these four microorganisms. In E. coli lgt mutant SK634, Gly-104 in this region was mutated to Ser, and the mutant organism was temperature sensitive in growth and exhibited low LGT activity in vitro. Diethylpyrocarbonate inactivated the E. coli LGT with a second-order rate constant of 18.6 M-1S-1, and the inactivation of LGT activity was reversed by hydroxylamine at pH 7. The inactivation kinetics were consistent with the modification of a single residue, His or Tyr, essential for LGT activity.

Amino Acid Sequence↗

PubMed1993

Protein, cDNA, and genomic DNA sequences of the towel gourd trypsin inhibitor. A squash family inhibitor.

Two trypsin inhibitor components of the squash family were isolated and purified from the juice of the towel gourd (Luffa cylindrica) using anhydrotrypsin affinity chromatography followed by high pressure liquid chromatography. The inhibitors were sequenced and found to consist of 28 and 29 amino acid residues. The determined sequences show high similarity to other inhibitors of the squash family, especially in the location of disulfide bonds and the reactive site and also in the COOH-terminal region. A cDNA library of towel gourd was constructed and used as a template for polymerase chain reaction amplification of two cDNA fragments of the inhibitor with an overlapping sequence. A full-length cDNA sequence coding for the inhibitor was then completed. The open reading frame codes for a prepro-inhibitor protein with the pre- and pro-peptides consisting of 21 and 13 residues, respectively. The deduced amino acid sequence of 29 residues for the inhibitor is consistent with that determined by primary structure analysis. The genomic sequence of the mature inhibitor was also ascertained using the total DNA of the towel gourd as a polymerase chain reaction template. The genomic sequence is completely identical with that of the cDNA, showing no intervening sequence.

Amino Acid Sequence↗

PubMed1992

Isolation and purification of HSV-1 specific transfer factor produced by HSV-1 immunized goat leukocyte dialysate.

A herpes simplex virus type 1 (HSV-1)-specific transfer factor (TF), was separated and purified from the leukocyte dialysate of goats immunized with HSV-1 using affinity chromatography on antigen-sorbent and reversed phase high performance liquid chromatography (RP-HPLC). The antigen-specific activities of the starting dialysate and the isolated TF component (s) were examined by 51Cr-labelled leukocyte adherence inhibition (51Cr LAI) assay. The analytical hydrophobic interaction HPLC (HI-HPLC) and isoelectric focusing (IEF) techniques were employed to evaluate the purity and the isoelectric point (PI) of isolated TF component(s). The experiments provided a two-step procedure for purifying the TF material from the starting dialysate. It seems that the purified active TF component (PTFC) was specific for HSV-1. The specific PTFC activity was increased 10,000-fold as compared with the activity of the dialysate. The active moiety appeared as a single band in the IEF gel as demonstrated by silver staining; it was hydrophilic and its PI was pH 4.48.

Animals↗

PubMed1992

Chemical characterization of the purified component of specific transfer factor in the leukocyte dialysates from HSV-1 immunized goats.

The chemical characterization of the purified component responsible for HSV-1 specific transfer factor activity (PTFC) by high resolution analytical methods was performed. PTFC had a molecular weight of 6,000 dalton by the size-exclusion HPLC analysis; it showed a marked UV-absorbance spot at 254 nm and a fluorescent spot at 366 nm on the thin-layer plate by thin-layer chromatography which spots coincided at the same place of the plate. The amino acid composition and sequencing analyses showed that PTFC consisted of at least twelve different amino acids, but the amino acid sequence could not be determined. The combined results indicate that PTFC is a compound with a molecular weight of 6,000 dalton, composed of peptide and nucleotide-like material. The peptide is rich in aspartic acid and its N-terminal end may be blocked.

Amino Acids↗

PubMed1990

Interspecific protoplast fusion in Streptomyces--selection of thermotolerant antibiotic-producing recombinant.

The thermotolerant fusants were obtained after interspecific protoplast fusion between S. qingfengmyceticus M15S (SMr, stop growth at 39 degrees C, producing qingfingmycin with wide antimicrobial spectrum) and S. hygroscopicus var. jinggangensis *75 (SMs, grow well at 42 degrees C, producing jingganmycin of antifungus) by directly selecting from the regeneration plates containing SM 100 micrograms/ml and incubated at 42 degrees C. The fusion frequency was about 10(-5) -10(-4). The stable thermotolerant recombinants with antimicrobial activity were obtained. The properties of their products were quite different from that of the parents (Qm, Jm). The antimicrobial substance produced by recombinant F6-6 consists of two components: one has acid-alkaline indicator property; the other is fluorescent under UV light. The antimicrobial products of F1-16, F1-38 and FM3-32 have absorption peaks at 274nm, which suggests that a cytosine moiety may be present in their molecules.

Anti-Bacterial Agents↗