Annie P-C Chen's scientific contributionswhile working at Academia Sinica (Taipei, Taiwan) and other institutions

Publications (6)

Publications citing this author (194)

    • Taken together, we hence suggest that the six TCM phytoextracts reported here can inhibit SARS-CoV replication with little or no cytotoxicity to Vero E6 cells, and are may thus serve as useful candidates for future development of anti-SARS therapeutics. The SARS-CoV 3CL protease is involved in the viral maturation process by cleaving the virus-encoded polyproteins (Chen et al., 2002). Because of its pivotal role in the SARS-CoV life cycle, the 3CL protease is recognized as an important target for discovery of anti-SARS-CoV agents.
    [Show abstract] [Hide abstract] ABSTRACT: Development of anti-severe acute respiratory syndrome associated coronavirus (SARS-CoV) agents is pivotal to prevent the reemergence of the life-threatening disease, SARS. In this study, more than 200 extracts from Chinese medicinal herbs were evaluated for anti-SARS-CoV activities using a cell-based assay that measured SARS-CoV-induced cytopathogenic effect (CPE) in vitro on Vero E6 cells. Six herbal extracts, one each from Gentianae Radix (龍膽 lóng dǎn; the dried rhizome of Gentiana scabra), Dioscoreae Rhizoma (山藥 shān yào; the tuber of Dioscorea batatas), Cassiae Semen (決明子 jué míng zǐ; the dried seed of Cassia tora) and Loranthi Ramus (桑寄生 sāng jì shēng; the dried stem, with leaf of Taxillus chinensis) (designated as GSH, DBM, CTH and TCH, respectively), and two from Rhizoma Cibotii (狗脊 gǒu jǐ; the dried rhizome of Cibotium barometz) (designated as CBE and CBM), were found to be potent inhibitors of SARS-CoV at concentrations between 25 and 200 μg/ml. The concentrations of the six extracts needed to inhibit 50% of Vero E6 cell proliferation (CC 50) and 50% of viral replication (EC 50) were determined. The resulting selective index values (SI = CC 50 /EC 50) of the most effective extracts CBE, GSH, DBM, CTH and TCH were > 59.4, > 57.5, > 62.1, > 59.4, and > 92.9, respectively. Among these extracts, CBM and DBM also showed significant inhibition of SARS-CoV 3CL protease activity with IC 50 values of 39 μg/ml and 44 μg/ml, respectively. Our findings suggest that these six herbal extracts may have potential as candidates for future development of anti-SARS therapeutics.
    Full-text · Article · Oct 2011
    • However, these bisphosphonates all bear substantial negative charge at physiological pH, which limit the compounds' ability to penetrate the cell membrane. In an effort to circumvent this perceived limitation , some biodegradable protecting groups have been used to mask a negative charge until after penetration of the cell membrane [18,19]. Further investigation and improvement of bisphosphonates are still required.
    [Show abstract] [Hide abstract] ABSTRACT: Background: Mevalonate pathway is an important cellular metabolic pathway present in all higher eukaryotes and many bacteria. Four enzymes in mevalonate pathway, including MVK, PMK, MDD, and FPPS, play important regulatory roles in cholesterol biosynthesis and cell proliferation. Methods: The following methods were used: cloning, expression and purification of enzymes in mevalonate pathway, organic syntheses of multifunctional enzyme inhibitors, measurement of their IC50 values for above four enzymes, kinetic studies of enzyme inhibitions, molecular modeling studies, cell viability tests, and fluorescence microscopy. Results and conclusions: We report our multi-target-directed design, syntheses, and characterization of two blue fluorescent bisphosphonate derivatives compounds 15 and 16 as multifunctional enzyme inhibitors in mevalonate pathway. These two compounds had good inhibition to all these four enzymes with their IC50 values at nanomolar to micromolar range. Kinetic and molecular modeling studies showed that these two compounds could bind to the active sites of all these four enzymes. The fluorescence microscopy indicated that these two compounds could easily get into cancer cells. General significance: Multifunctional enzyme inhibitors are generally more effective than single enzyme inhibitors, with fewer side effects. Our results showed that these multifunctional inhibitors could become lead compounds for further development for the treatment of soft-tissue tumors and hypercholesteremia.
    Full-text · Article · Feb 2013
    • The principal mechanism for cis-and trans-type enzymes is similar . For both an ionization–condensation–elimination mechanism has been proposed (Liang et al., 2002; Chang et al., 2004 ) that is applied several times, if several IPP molecules are used to yield the final product (Fig. 12). At the beginning of the reaction, a prenyl pyrophosphate (e.g.
    [Show abstract] [Hide abstract] ABSTRACT: General thermodynamic calculations using the semiempiric PM3 method have led to the conclusion that prenyldiphosphate converting enzymes require at least one divalent metal cation for the activation and cleavage of the diphosphate-prenyl ester bond, or they must provide structural elements for the efficient stabilization of the intermediate prenyl cation. The most important common structural features, which guide the product specificity in both terpene synthases and aromatic prenyl transferases are aromatic amino acid side chains, which stabilize prenyl cations by cation-pi interactions. In the case of aromatic prenyl transferases, a proton abstraction from the phenolic hydroxyl group of the second substrate will enhance the electron density in the phenolic ortho-position at which initial prenylation of the aromatic compound usually occurs. A model of the structure of the integral transmembrane-bound aromatic prenyl transferase UbiA was developed, which currently represents the first structural insight into this group of prenylating enzymes with a fold different from most other aromatic prenyl transferases. Based on this model, the structure-activity relationships and mechanistic aspects of related proteins, for example those of Lithospermum erythrorhizon or the enzyme AuaA from Stigmatella aurantiaca involved in the aurachin biosynthesis, were elucidated. The high similarity of this group of aromatic prenyltransferases to 5-epi-aristolochene synthase is an indication of an evolutionary relationship with terpene synthases (cyclases). This is further supported by the conserved DxxxD motif found in both protein families. In contrast, there is no such relationship to the aromatic prenyl transferases with an ABBA-fold, such as NphB, or to any other known family of prenyl converting enzymes. Therefore, it is possible that these two groups might have different evolutionary ancestors.
    Full-text · Article · Oct 2009
    • This result shows that TEAS does not deprive FPP of the C40 carotenoid pathway. Considering that the prenyltransferases have a much high turnover rate (kcat∼1 sec−1, for example, ref. [32]–[34]) than that of TEAS (0.04 sec−1) [35], it is conceivable that CrtE, a GGPP synthase, was efficient enough to convert the available FPP into GGPP and was unaffected by the co-existence of TEAS. Note that most (if not all) reported sesquiTPSs have kcat values similar to that of TEAS (for example, see [36]–[38]).
    [Show abstract] [Hide abstract] ABSTRACT: Terpene synthases catalyze the formation of a variety of terpene chemical structures. Systematic mutagenesis studies have been effective in providing insights into the characteristic and complex mechanisms of C-C bond formations and in exploring the enzymatic potential for inventing new chemical structures. In addition, there is growing demand to increase terpene synthase activity in heterologous hosts, given the maturation of metabolic engineering and host breeding for terpenoid synthesis. We have developed a simple screening method for the cellular activities of terpene synthases by scoring their substrate consumption based on the color loss of the cell harboring carotenoid pathways. We demonstrate that this method can be used to detect activities of various terpene synthase or prenyltransferase genes in a high-throughput manner, irrespective of the product type, enabling the mutation analysis and directed evolution of terpene synthases. We also report the possibility for substrate-specific screening system of terpene synthases by taking advantage of the substrate-size specificity of C30 and C40 carotenoid pathways.
    Full-text · Article · Mar 2014
    • 9. All the residues suggested to be involved in the catalysis for E. coli UPPS [40], namely D79, N81, R83, H96, S124, N127, and R130 (numbering according to AtCPT6) were conserved between these remote organisms (eukaryotic and prokaryotic), indicating the location of the AtCPT6 active center (Figs. 8, 9). On the other hand, residues comprising fragment of helix α3 and the loop between α3 and βC defined earlier as important for determination of the polyprenol chain length [7,41], highlighted by the blue box inFig.
    [Show abstract] [Hide abstract] ABSTRACT: cis-Prenyltransferases (CPTs) comprise a numerous enzymes synthesizing isoprenoid hydrocarbon skeleton with isoprenoid units in the cis (Z) configuration. The chain-length specificity of a particular plant CPT is in most cases unknown despite the composition of the accumulated isoprenoids in the tissue of interest being well established. In this report AtCPT6, one of the nine Arabidopsis thaliana CPTs, is shown to catalyze the synthesis of a family of very short-chain polyisoprenoid alcohols of six, seven, and eight isoprenoid units, those of seven units dominating. The product specificity of AtCPT6 was established in vivo following its expression in the heterologous system of the yeast Saccharomyces cerevisiae and was confirmed by the absence of specific products in AtCPT6 T-DNA insertion mutants and their overaccumulation in AtCPT6 - overexpressing plants. These observations are additionally validated in silico using an AtCPT6 model obtained by homology modeling. AtCPT6 only partially complements the function of the yeast homologue of CPT - Rer2 since it restores the growth but not protein glycosylation in rer2Δ yeast. This is the first in planta characterization of specific products of a plant CPT producing polyisoprenoids. Their distribution suggests that a joint activity of several CPTs is required to produce the complex mixture of polyisoprenoid alcohols found in Arabidopsis roots.
    Full-text · Article · Nov 2013