Biomedical subjects

Liang Feng

Publications and source records attributed to Liang Feng.

30 records · Page 2Linked to original sources

PubMed2004

Molecular mechanism of AHSP-mediated stabilization of alpha-hemoglobin.

Hemoglobin A (HbA), the oxygen delivery system in humans, comprises two alpha and two beta subunits. Free alpha-hemoglobin (alphaHb) is unstable, and its precipitation contributes to the pathophysiology of beta thalassemia. In erythrocytes, the alpha-hemoglobin stabilizing protein (AHSP) binds alphaHb and inhibits its precipitation. The crystal structure of AHSP bound to Fe(II)-alphaHb reveals that AHSP specifically recognizes the G and H helices of alphaHb through a hydrophobic interface that largely recapitulates the alpha1-beta1 interface of hemoglobin. The AHSP-alphaHb interactions are extensive but suboptimal, explaining why beta-hemoglobin can competitively displace AHSP to form HbA. Remarkably, the Fe(II)-heme group in AHSP bound alphaHb is coordinated by the distal but not the proximal histidine. Importantly, binding to AHSP facilitates the conversion of oxy-alphaHb to a deoxygenated, oxidized [Fe(III)], nonreactive form in which all six coordinate positions are occupied. These observations reveal the molecular mechanisms by which AHSP stabilizes free alphaHb.

Animals↗

PubMed2004

Biosensor for the determination of sorbitol based on molecularly imprinted electrosynthesized polymers.

Despite the increasing number of applications of biosensors in many fields, the construction of a steady biosensor remains still challenging. The high selectivity and stability of molecularly imprinted polymers for the template molecule make them ideal alternatives as recognition elements for sensors. In this work, the fabrication and characterization of biosensor based on molecularly imprinted electrosynthesized polymers is reported as the first case of imprinting sorbitol. A relevant molecularly imprinted film is prepared by o-phenylenediamine (o-PD) using the electrochemical method. Quartz crystal microbalance is employed as a sensitive apparatus of biosensor for the determination of sorbitol. An equation is deduced to characterize the interaction between molecularly imprinted films and the template. A linear relationship between the frequency shift and the concentration of analyte in the range of 1-15 mM was found. The detection limit is about 1mM.

Biosensing Techniques↗

PubMed2004

Aminoacyl-tRNA synthesis by pre-translational amino acid modification.

Aminoacyl-tRNAs (aa-tRNAs) are essential substrates for ribosomal translation, and are generally synthesized by aminoacyl-tRNA synthetases (aaRSs). It was expected earlier that every organism would contain a complete set of twenty aaRSs, one for each canonical amino acid. However, analysis of the many known genome sequences and biochemical studies revealed that most organisms lack asparaginyl- and glutaminyl-tRNA synthetases, and thus are unable to attach asparagine and glutamine directly onto their corresponding tRNA. Instead, a pretranslational amino acid modification is required to convert Asp-tRNA(Asn) and Glu-tRNA(Gln) to the correctly charged Asn-tRNA(Asn) and Gln-tRNA(Gln), respectively. This transamidation pathway of amide aa-tRNA synthesis is common in most bacteria and archaea. Unexpected results from biochemical, genetic and genomic studies showed that a large variety of different bacteria rely on tRNA-dependent transamidation for the formation of the amino acid asparagine. Pretranslational modifications are not restricted to asparagine and glutamine but are also found in the biosynthesis of some other aa-tRNAs, such as the initiator tRNA fmet-tRNA(Met)(i) and Sec-tRNA(Sec) specifying selenocysteine, the 21(st) cotranslationally inserted amino acid. tRNA-dependent amino acid modification is also involved in the generation of aminolevulinic acid, the first precursor for porphyrin biosynthesis in many organisms.

Amino Acids↗

PubMed2004

Molecularly imprinted TiO2 thin film by liquid phase deposition for the determination of L-glutamic acid.

For the first time, the feasibility of a molecularly imprinted liquid phase deposition (LPD) thin film has been demonstrated. Thin films of titanium oxide imprinted with L-glutamic acid were prepared by the LPD method on a gold-coated quartz crystal microbalance. The imprinted molecule could be removed upon treatment with immersion in deionized water. A sensor was developed on the basis of this method and showed good sensitivity, selectivity, and reproducibility to the template molecule. An equation was deduced to characterize the interaction between molecularly imprinted films and the template by virtue of Scatchard analysis. X-ray photoelectron spectroscopy was introduced to show the evidence for the molecular imprinting phenomenon. The linear relationship between the frequency shifts and the concentration of analyte in the range of 10-200 microM was obtained. LPD proves to be a powerful method for imprinting titanium oxide thin films.

Biosensing Techniques↗

PubMed2004

[Determination of total, soluble and insoluble dietary fiber in foods].

OBJECTIVE: To determinate the total, soluble and insoluble dietary fiber in different kinds of food so as to provide the references for guiding the diet for control and prevention of chronic diseases. METHODS: The contents of total, soluble and insoluble dietary fiber in 33 food samples were determined by enzymatic-gravimetric method. RESULTS: The average total dietary fiber(TDF, g/100 g edible part) in dry beans, flesh beans and whole grains were 36%, 14%, 16% respectively, and that of refine grains, vegetables and fruits were lower than 10%. The contents of soluble dietary fiber in beans were highest, and the contents of insoluble dietary fiber in dry beans and other grains were higher. CONCLUSION: The repeatability of the analysis method was good, the contents and pattern of dietary fiber in different kinds of food were largely varied.

Dietary Fiber↗

PubMed2004

[Studies on IgG antibodies of SARS patients].

OBJECTIVE: To investigate the significance of detecting specific serum IgG antibodies in clinical diagnosis of SARS as well as affecting factors. METHODS: Enzyme-linked immunoassay kit for SARS coronavirus antibodies developed by HuaDa Biological Company was applied to detect specific serum IgG from SARS patients and the production of SARS specific antibodies among patients of different age groups, sex and with or without steroid treatment were statistically compared. RESULTS: Out of 121 patients studied, 71.1% were SARS specific IgG positive. Patients younger than 15 years, between 15 to 59 years, older than 59 years had positive rates of 60.0%, 70.2%, and 85.7%, respectively with no statistically significance (P=0.766); patients with or without steroid treatment showed positive rates of 70.6% and 72.4%, respectively (P=0.84); patients exhibiting either severe or light syndromes showed positive rates of 78.1% and 67.4%, respectively (P=0.493); both male and female patients showed the same positive rate of 71.1%. CONCLUSION: The sensitivity of the SARS specific IgG kit utilized needs to be further improved. The production of SARS IgG is not notably correlated with sex, age, seriousness of symptoms, and steroid treatment.

Adolescent↗

PubMed2004

[Pathological development of researches on intervertebral disc degeneration].

This article reviews the literature about the etiology and pathology of intervertebral disc degeneration. The degeneration of intervertebral disc is associated with certain biomechanical factor. Stress can directly lead to the rupture of intervertebral disc and, more importantly, change its biological properties. And then, it can trigger the process of degeneration via inflammatory mechanism which may include autoimmunity.

Biomechanical Phenomena↗

PubMed2003

Expanding tRNA recognition of a tRNA synthetase by a single amino acid change.

Aspartyl-tRNA synthetase (AspRS) occurs in two types: the discriminating enzyme (D-AspRS) forms only Asp-tRNA(Asp), whereas the nondiscriminating enzyme (ND-AspRS) also synthesizes Asp-tRNA(Asn), which is a required intermediate for protein synthesis in many organisms. We attempted to expand the tRNA recognition of the discriminating Thermococcus kodakaraensis AspRS to that of a ND-AspRS by in vitro mutagenesis. An alignment of 26 archaeal AspRS proteins revealed two positions (26 and 85 in the T. kodakaraensis sequence) whose amino acid identity changes according to the enzymes' tRNA specificity. In their anticodon-binding domain, D-AspRS proteins contain W26 (or Q26) and K85, compared with H26 and P85 in the ND-AspRSs. T. kodakaraensis AspRS gained the ability to form Asp-tRNA(Asn) in vitro when the W26H or K85P changes were introduced independently or in combination. In the aminoacylation of tRNA(Asn) or tRNA(Asp) transcripts, the mutant enzymes displayed at least a 100- to 500-fold change in tRNA specificity, as judged by the ratio of the k(cat)K(m) values of Asp-tRNA(Asp) vs. Asp-tRNA(Asn) formation. That T. kodakaraensis mutant AspRSs mischarge tRNA(Asn) was also manifested in the higher level (1.7%) of aspartylation of unfractionated Pyrococcus tRNA compared with that achieved by the wild-type enzyme (0.9%). Northern blot analysis of the Asp-tRNA separated by acidurea gel electrophoresis confirmed the in vitro synthesis of Asp-tRNA(Asn). A structure-based model points to a direct interaction of K85 in T. kodakaraensis AspRS with the anticodon nucleotide C36 of tRNA(Asp). Thus, a switch between D-AspRS and ND-AspRS enzymes could have evolved with only limited amino acid changes.

Amino Acid Sequence↗

PubMed2002

Evolutionary divergence of the archaeal aspartyl-tRNA synthetases into discriminating and nondiscriminating forms.

Asparaginyl-tRNA (Asn-tRNA) is generated in nature via two alternate routes, either direct acylation of tRNA with asparagine by asparaginyl-tRNA synthetase (AsnRS) or in a two-step pathway that requires misacylated Asp-tRNA(Asn) as an intermediate. This misacylated aminoacyl-tRNA is formed by a nondiscriminating aspartyl-tRNA synthetase (AspRS), an enzyme that in addition to forming Asp-tRNA(Asp) also misacylates tRNA(Asn). In contrast, a discriminating AspRS cannot acylate tRNA(Asn). It has been suggested that the archaeal AspRS enzymes are nondiscriminating, whereas the bacterial ones discriminate. The archaeal and bacterial AspRS proteins are indeed distinct in sequence and structure. However, we show that both discriminating and nondiscriminating forms of AspRS exist among the archaea. Using unfractionated methanobacterial and pyrococcal tRNA, the Methanothermobacter thermautotrophicus AspRS acylated approximately twice as much tRNA as did AspRS from Pyrococcus kodakaraensis or Ferroplasma acidarmanus. Proof that Asp-tRNA(Asn) was generated by the methanogen synthetase was the conversion of Asp-tRNA formed by M. thermautotrophicus AspRS to Asn-tRNA by M. thermautotrophicus Asp-tRNA(Asn) amidotransferase. In contrast, Asp-tRNA formed by the Pyrococcus or Ferroplasma enzymes was not a substrate for the amidotransferase. Also, although all three AspRS enzymes charged tRNA(Asp) transcripts, only M. thermautotrophicus AspRS aspartylated the tRNA(Asn) transcript. Genomic analysis provides a rationale for the nature of these enzymes. The mischarging AspRS correlates with the absence in the genome of AsnRS and the presence of Asp-tRNA(Asn) amidotransferase, employed by the transamidation pathway. In contrast, the discriminating AspRS correlates with the absence of the amidotransferase and the presence of AsnRS, forming Asn-tRNA by direct aminoacylation. The high sequence identity, up to 60% between discriminating and nondiscriminating archaeal AspRSs, suggests that few mutational steps may be necessary to convert the tRNA-discriminating ability of a tRNA synthetase.

Aspartate-tRNA Ligase↗

PubMed2002

[Localization diagnosis of chyluria by radionuclide lymphoscintigraphy].

OBJECTIVE: To study the effect of radionuclide lymphoscintigraphy, a new method of localization diagnosis of chyluria. METHODS: Radionuclide lymphoscintigraphy was used to examine 34 patients with chyluria and the results of radionuclide lymphoscintigraphy was compared with those of cystoscopy and lymphangiography. RESULTS: Among the 34 patients 85.3% of unilateral localization diagnosis by radionuclide lymphoscintigraphy was coincident with that by cystoscopy. The positive rate of bilateral localization diagnosis was higher than that by cystoscopy. CONCLUSION: A less invasive technique, radionuclide lymphoscintigraphy can be used as a new option for the localization diagnosis of chyluria.

Adult↗

PubMed2002

Aminoacyl-tRNA formation in the extreme thermophile Thermus thermophilus.

Thermophilic organisms must be capable of accurate translation at temperatures in which the individual components of the translation machinery and also specific amino acids are particularly sensitive. Thermus thermophilus is a good model organism for studies of thermophilic translation because many of the components in this process have undergone structural and biochemical characterization. We have focused on the pathways of aminoacyl-tRNA synthesis for glutamine, asparagine, proline, and cysteine. We show that the T. thermophilus prolyl-tRNA synthetase (ProRS) exhibits cysteinyl-tRNA synthetase (CysRS) activity although the organism also encodes a canonical CysRS. The ProRS requires tRNA for cysteine activation, as is known for the characterized archaeal prolyl-cysteinyl-tRNA synthetase (ProCysRS) enzymes. The heterotrimeric T. thermophilus aspartyl-tRNA(Asn) amidotransferase can form Gln-tRNA in addition to Asn-tRNA: however, a 13-amino-acid C-terminal truncation of the holoenzyme A subunit is deficient in both activities when assayed with homologous substrates. A survey of codon usage in completed prokaryotic genomes identified a higher Glu:Gln ratio in proteins of thermophiles compared to mesophiles.

Amino Acyl-tRNA Synthetases↗

PubMed2002

Crystal structure of a staphylokinase: variant a model for reduced antigenicity.

Staphylokinase (SAK) is a 15.5-kDa protein from Staphylococcus aureus that activates plasminogen by forming a 1 : 1 complex with plasmin. Recombinant SAK has been shown in clinical trials to induce fibrin-specific clot lysis in patients with acute myocardial infarction. However, SAK elicits high titers of neutralizing antibodies. Biochemical and protein engineering studies have demonstrated the feasibility of generating SAK variants with reduced antigenicity yet intact thrombolytic potency. Here, we present X-ray crystallographic evidence that the SAK(S41G) mutant may assume a dimeric structure. This dimer model, at 2.3-A resolution, could explain a major antigenic epitope (residues A72-F76 and residues K135-K136) located in the vicinity of the dimer interface as identified by phage-display. These results suggest that SAK antigenicity may be reduced by eliminating dimer formation. We propose several potential mutation sites at the dimer interface that may further reduce the antigenicity of SAK.

Antigens, Bacterial↗