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Biomedical subjects

Fan Xiao

Publications and source records attributed to Fan Xiao.

12 recordsLinked to original sources
PubMed2007

Aggregation of prion protein with insertion mutations is proportional to the number of inserts.

Mutation in the prion gene, PRNP, accounts for approx. 10-15% of human prion diseases. However, little is known about the mechanisms by which a mutant prion protein (PrP) causes disease. We compared the biochemical properties of a wild-type human prion protein, rPrP(C) (recombinant wild-type PrP), which has five octapeptide-repeats, with two recombinant human prion proteins with insertion mutations, one with three more octapeptide repeats, rPrP(8OR), and the other with five more octapeptide repeats, rPrP(10OR). We found that the insertion mutant proteins are more prone to aggregate, and the degree and kinetics of aggregation are proportional to the number of inserts. The octapeptide-repeat and alpha-helix 1 regions are important in aggregate formation, because aggregation is inhibited with monoclonal antibodies that are specific for epitopes in these regions. We also showed that a small amount of mutant protein could enhance the formation of mixed aggregates that are composed of mutant protein and wild-type rPrP(C). Accordingly, rPrP(10OR) is also more efficient in promoting the aggregation of rPrP(C) than rPrP(8OR). These findings provide a biochemical explanation for the clinical observations that the severity of the disease in patients with insertion mutations is proportional to the number of inserts, and thus have implications for the pathogenesis of inherited human prion disease.

Antibodies, Monoclonal↗
PubMed2006

Test for detection of disease-associated prion aggregate in the blood of infected but asymptomatic animals.

We have developed a sensitive in vitro assay for detecting disease-associated prion aggregates by combining an aggregation-specific enzyme-linked immunosorbent assay (AS-ELISA) with the fluorescent amplification catalyzed by T7 RNA polymerase technique (FACTT). The new assay, named aggregation-specific FACTT (AS-FACTT), is much more sensitive than AS-ELISA and could detect prion aggregates in the brain of mice as early as 7 days after an intraperitoneal inoculation of PrP(Sc). However, AS-FACTT was still unable to detect prion aggregates in blood of infected mice. To further improve the detection limit of AS-FACTT, we added an additional prion amplification step (Am) and developed a third-generation assay, termed Am-A-FACTT. Am-A-FACTT has 100% sensitivity and specificity in detecting disease-associated prion aggregates in blood of infected mice at late but still asymptomatic stages of disease. At a very early stage, Am-A-FACTT had a sensitivity of 50% and a specificity of 100%. Most importantly, Am-A-FACTT also detects prion aggregates in blood of mule deer infected with the agent causing a naturally occurring prion disease, chronic wasting disease. Application of this assay to cattle, sheep, and humans could safeguard food supplies and prevent human contagion.

Animals↗
PubMed2006

Selection of CC chemokine receptor 5-binding peptide from a phage display peptide library.

Human CC chemokine receptor (CCR) 5 is a G protein-coupled receptor involved in a broad range of human diseases that mediates HIV-1 viral entry into cells. Certain small molecule receptor antagonists to CCR5 have been useful in therapy for these diseases. In this study, CCR5-expressing CHO cells (CHO/CCR5 cells) were used to select CCR5-binding peptides from a phage-displayed 12-mers peptide library. All of the 30 clones selected from the library showed specific binding to CHO/CCR5 cells by enzyme linked immunosorbent assay (ELISA). Seventeen out of the 30 clones shared the amino acid motif AFDWTFVPSLIL. The motif-containing phages and synthetic peptide AFDWTFVPSLIL blocked the binding of mAb 2D7 to CHO/CCR5 cells and competitively inhibited the ability of chemokine regulated on activation normal T cell expressed and secreted (RANTES) binding to CHO/CCR5 cells. Furthermore, the peptide AFDWTFVPSLIL also inhibited RANTES induced increase in the intracellular Ca2+ level in CHO/CCR5 cells. These results suggest that the peptide AFDWTFVPSLIL was specific for CCR5 and that it might become a CCR5 antagonist.

Amino Acid Motifs↗
PubMed2006

Prion proteins with insertion mutations have altered N-terminal conformation and increased ligand binding activity and are more susceptible to oxidative attack.

We compared the biochemical properties of a wild type recombinant normal human cellular prion protein, rPrP(c), with a recombinant mutant human prion protein that has three additional octapeptide repeats, rPrP(8OR). Monoclonal antibodies that are specific for the N terminus of rPrP(c) react much better with rPrP(8OR) than rPrP(c), suggesting that the N terminus of rPrP(8OR) is more exposed and hence more available for antibody binding. The N terminus of PrP(c) contains a glycosaminoglycan binding motif. Accordingly, rPrP(8OR) also binds more glycosaminoglycan than rPrP(c). In addition, the divalent cation copper modulates the conformations of rPrP(c) and rPrP(8OR) differently. When compared with rPrP(c), rPrP(8OR) is also more susceptible to oxidative damage. Furthermore, the abnormalities associated with rPrP(8OR) are recapitulated, but even more profoundly, in another insertion mutant, which has five extra octapeptide repeats, rPrP(10OR). Therefore, insertion mutants appear to share common features, and the degree of abnormality is proportional to the number of insertions. Any of these anomalies may contribute to the pathogenesis of inherited human prion disease.

Amino Acid Motifs↗
PubMed2006

Polymorphisms in the promoter region of the angiotensinogen gene are associated with liver cirrhosis in patients with chronic hepatitis B.

BACKGROUND AND AIMS: It is known that the renin-angiotensin system (RAS) regulates fibrosis. Polymorphisms in the genes of the RAS may contribute to the outcome of liver cirrhosis. Angiotensinogen (AGT), mainly produced in the liver, is the substrate of renin. The aim of this study was to determine whether polymorphisms in the promoter region of the AGT gene are associated with liver cirrhosis in patients with chronic hepatitis B. METHODS: Restriction fragment length polymorphism PCR was used to study polymorphisms in the promoter region of the AGT gene in patients with liver cirrhosis and in a control population. Four polymorphisms were assayed: G-217A, G-152A, A-20C and A-6G. RESULTS: A statistically significant relationship was seen between polymorphisms of the AGT core promoter region and liver cirrhosis in patients with chronic hepatitis B (A-20C, P = 0.007; A-6G, P = 0.042). However, the distributions of the AGT-217 and AGT-152 genotypes were not significantly different from the control population (P = 0.615 and P = 0.170, respectively). CONCLUSIONS: Polymorphisms of the core promoter region of the AGT gene (AGT-20 and AGT-6) were associated with liver cirrhosis in patients with chronic hepatitis B.

Alleles↗
PubMed2006

[Expression of human tumstatin in Pichia pastoris and its bioactivity].

Human tumstatin(hTumstatin)cDNA was amplified from recombinant plasmid pET-3c-tum, cloned in frame with the signal sequence in yeast vector pPICZalphaA and transformed into Pichia pastoris GS115 by electroporation. The expression of hTumstatin in GS115(pPICZalpha-tum)was then induced by methanol and secreted into the culture medium, with a yield of 25mg/L as shown by SDS-PAGE and Western blotting. The expressed hTumstatin was purified to more than 85% purity using a simple one-step SP-Sepharose cation exchange chromatography. The MTT and chick chorioallantoic membrane assay showed that the yeast produced hTumstatin could inhibit the proliferation of human umbilical vein endothelial cells and the neovascularization induced by bFGF. Hoechst 33258 fluorescent staining also demonstrated the apoptotic change in endothelial cellular nuclear morphology.

Angiogenesis Inhibitors↗
PubMed2004

Dibenzyl bromophenols with diverse dimerization patterns from the brown alga Leathesia nana.

Six novel dibenzyl bromophenols (1-6) with different dimerization patterns and two propyl bromophenol derivatives (7 and 8), together with 11 known bromophenol derivatives, were isolated from the ethanolic extract of the brown alga Leathesia nana. On the basis of spectroscopic methods the structures of the new compounds were determined as 5,6'-diethyloxymethyl-3,4,2'-tribromo-2,3',4'-trihydroxydiphenyl ether (1), 2-(2,3-dibromo-4,5-dihydroxybenzyl)-3,5-dihydroxy-4-methoxybenzyl alcohol (2), 6-(2,3-dibromo-4,5-dihydroxybenzyl)-2,3-dibromo-4,5-dihydroxy benzyl methyl ether (3), 9,10-dihydro-9,10-dimethoxy-3,4,7,8-tetrabromo-1,2,5,6-tetrahydroxyanthracene (4), (+)-3-(2,3-dibromo-4,5-dihydroxyphenyl)-4-bromo-5,6-dihydroxy-1,3-dihydroisobenzofuran (5), rel-(4aS,10aR)-(+/-)-6,7-dibromo-4a-hydroxy-3,8-dihydroxymethyl-10a-methoxy-1,4,4a,10a-tetrahydrodibenzo[b,e][1,4]dioxin-1-one (6), (E)-2-methyl-3-(2,3-dibromo-4,5-dihydroxyphenyl)propenal (7), and 2-methyl-3-(2,3-dibromo-4,5-dihydroxyphenyl)-1-propanol (8). Some compounds including 3 showed in vitro selective cytotoxicity against several human cancer cell lines. This is the first brown alga to be reported containing bromophenols.

China↗
PubMed2004

Frames of reference in mobile augmented reality displays.

In 3 experiments, the authors investigated spatial updating in augmented reality environments. Participants learned locations of virtual objects on the physical floor. They were turned to appropriate facing directions while blindfolded before making pointing judgments (e.g., "Imagine you are facing X. Point to Y"). Experiments manipulated the angular difference between the learning heading and the imagined heading and between the actual heading and the imagined heading. The effect of actual-imagined on pointing latency was observed for naive users but not for users with brief training or instructions concerning the fact that objects can move with body movements. The results indicated that naive users used an environment-stabilized reference frame to access information arrays, but with experience and instruction the nature of the representation changed from an environment stabilized to a body stabilized reference frame.

Environment↗
PubMed2003

Expression, purification and functional characterization of a recombinant scorpion venom peptide BmTXKbeta.

BmTXKbeta, a scorpion toxin isolated from the Chinese scorpion Buthus martensii Karsch (BmK), was expressed as a GST fusion protein in BL21 (DE3) strain. The recombinant GST-BmTXKbeta protein was purified by affinity chromatography. When treated with enterokinase, the GST-BmTXKbeta fusion protein released an approximate 6.5kDa protein which was the expected size for correctly processed. About 2mg purified recombinant BmTXKbeta protein (rBmTXKbeta) was produced from 1l bacterial culture, using this expression and purification system. The function of rBmTXKbeta was studied on the rabbit atrial myocyte by whole-cell patch clamp technique. The results showed that rBmTXKbeta inhibited the transient outward current (I(to)) of rabbit atrial myocyte with recovery after washout and the inhibition was concentration-dependent. The rBmTXKbeta prolonged the action potential duration of rabbit atrial myocyte in a concentration-dependent manner, whereas it did not affect the action potential amplitude.

Action Potentials↗
PubMed2003

Bioactivity of metallic biomaterials with anatase layers deposited in acidic titanium tetrafluoride solution.

A simple and versatile treatment was developed to provide various metallic biomaterials such as Ti, NiTi, Ta and SUS 316L stainless steel with in vitro bioactivity or ability to deposit carbonate-incorporated apatite in a simulated body fluid (Kokubo solution). A well-crystallized anatase layer deposited on the metallic biomaterials surfaces after soaking them at 60 degrees C for 24 h in an aqueous solution of titanium tetrafluoride (40 mM) whose pH was adjusted to 1.9 with HCl. The as-coated anatase layers did not deposit apatite. When heated at 300 degrees C they were so bioactive as to deposit apatite within 5 day(s) in the Kokubo solution. The trace amount of fluorine weakly bound in the as-coated anatase layers was suggested to be one of the factors that suppressed the bioactivity.

Journal Article↗
PubMed2003

[Analysis of the genomic organization of a novel scorpion toxin BmTXK beta].

Scorpion venoms contain different types of low molecular mass toxic peptides acting on ion channels. Many cDNAs and genomic genes encoding these toxins have been isolated and sequenced while the mechanisms of expression and regulation of scorpion toxins is not well studied yet. BmTXK beta, one of the four putative long-chain potassium channel toxins, is isolated from the cDNA library of the venom gland of Chinese scorpion BmK (Buthus martensii Karsch). It has an 886 bp intron located in the mature peptide while other scorpion toxins' introns are located in the signal peptide. The special genomic organization of BmTXK beta makes it a good object to study the mechanism of expression and regulation of scorpion toxins. With primers designed according to the already known sequence of BmTXK beta, its 5' and 3' flanking regions are cloned by the Vecttorette II Staorette Pack method and sequenced. Analysis of the sequence shows that another intron longer than 997 bp is located in the signal peptide region of BmTXK beta, which makes BmTXK beta different from all the other scorpion toxins that have no intron or only one intron in the signal peptide. The special genomic organization of BmTXK beta indicates that BmTXK beta is a new membership of long-chain potassium channel toxin.

Amino Acid Sequence↗