Browsing by Author "Chen, Chun-Chen"

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PPISearch: a web server for searching homologous protein-protein interactions across multiple species
(2009-07-01)
Chen, Chun-Chen
;
Lin, Chun-Yu
;
Lo, Yu-Shu
;
Yang, Jinn-Moon
;
生物科技學系
As an increasing number of reliable protein-protein interactions (PPIs) become available and high-throughput experimental methods provide systematic identification of PPIs, there is a growing need for fast and accurate methods for discovering homologous PPIs of a newly determined PPI. PPISearch is a web server that rapidly identifies homologous PPIs (called PPI family) and infers transferability of interacting domains and functions of a query protein pair. This server first identifies two homologous families of the query, respectively, by using BLASTP to scan an annotated PPIs database (290 137 PPIs in 576 species), which is a collection of five public databases. We determined homologous PPIs from protein pairs of homologous families when these protein pairs were in the annotated database and have significant joint sequence similarity (E <= 10(-40)) with the query. Using these homologous PPIs across multiple species, this sever infers the conserved domain domain pairs (Pfam and InterPro domains) and function pairs (Gene Ontology annotations). Our results demonstrate that the transferability of conserved domain-domain pairs between homologous PPIs and query pairs is 88% using 103 762 PPI queries, and the transferability of conserved function pairs is 69% based on 106 997 PPI queries. The PPISearch server should be useful for searching homologous PPIs and PPI families across multiple species. The PPISearch server is available through the website at http://gemdock.life.nctu.edu.tw/ppisearch/.
Rank-based interolog mapping for predicting protein-protein interactions between genomes
(2013-01-01)
Lo, Yu-Shu
;
Chen, Chun-Chen
;
Hsu, Kai-Cheng
;
Yang, Jinn-Moon
;
交大名義發表
As rapidly increasing number of sequenced genomes, the methods for predicting protein-protein interactions (PPIs) from one organism to another is becoming important. Best-match and generalized interolog mapping methods have been proposed for predicting (PPIs). However, best-match mapping method suffers from low coverage of the total interactome, because of using only best matches. Generalized interolog mapping method may predict unreliable interologs at a certain similarity cutoff, because of the homologs differed in subcellular compartment, biological process, or function from the query protein. Here, we propose a new "rank-based interolog mapping" method, which uses the pairs of proteins with high sequence similarity (E-value<10-10) and ranked by BLASTP Evalue in all possible homologs to predict interologs. First, we evaluated "rank-based interolog mapping" on predicting the PPIs in yeast The accuracy at selecting top 5 and top 10 homologs are 0.17, and 0.12, respectively, and our method outperformed generalized interolog mapping method (accuracy=0.04) with the joint E-value<10-70. Furthermore, our method was used to predict PPIs in four organisms, including worm, fly, mouse, and human. In addition, we used Gene Ontology (GO) terms to analyzed PPIs, which reflect cellular component, biological process, and molecular function, inferred by rank-based mapping method. Our rank-based mapping method can predict more reliable interactions under a given percentage of false positives than the best-match and generalized interolog mapping methods. We believe that the rank-based mapping method is useful method for predicting PPIs in a genome-wide scale.
Structural simulation and protein engineering to convert an endo-chitosanase to an exo-chitosanase
(2008-09-01)
Yao, Yueh-Yun
;
Shrestha, Keshab Lal
;
Wu, Yue-Jin
;
Tasi, Huei-Ju
;
Chen, Chun-Chen
To obtain an enzyme for the production of chito-disaccharides (GlcN(2)) by converting endo-chitosanase to exo-chitosanase, we chose an endo-chitosanase from Bacillus circulans MH-K1 (Csn) as the candidate for protein engineering. Using molecular modeling, two peptides with five amino acids (PCLGG) and six amino acids (SRTCKP) were designed and inserted after the positions of D(115) and T(222) of Csn, respectively. The inserted fragments are expected to form loops that might protrude from opposite walls of the substrate-binding cleft, thus forming a 'roof' over the catalytic site that might alter the product specificity. The chimeric chitosanase (Chim-Csn) and wild-type chitosanase (WT-Csn) were both over-expressed in Escherichia coli and purified nearly to homogeneity. The products formed from chitosan were analyzed by ESI-MS (electrospray ionization-mass spectrometry). A mixture of GlcN(2), GlcN(3) and GlcN(4) was obtained with WT-Csn, whereas Chim-Csn formed, with a smaller catalytic rate (3% of WT-Csn activity), GlcN(2) as the dominant product. Measurements of viscosity showed that, with similar amounts of enzyme activity, Chim-Csn catalyzed the hydrolysis of chitosan with a smaller rate of viscosity decrease than WT-Csn. The results indicate that, on inserting two surface loops, the endo-type chitosanase was converted into an exo-type chitosanase, which to our knowledge is the first chitosanase that releases GlcN(2) from chitosan as the dominant product.