A new drug design method, the multiple field three-dimensional quantitative structure-activity relationship (MF-3D-QSAR), is proposed. It is a combination and development of classical 2D-QSAR and traditional 3D-QSAR. In addition to the electrostatic and van der Waals potentials, more potential fields (such as lipophilic potential, hydrogen bonding potential, and nonthermodynamic factors) are integrated in the MF-3D-QSAR. Meanwhile, a principal component analysis (PCA) and iterative double least square (IDLS) technique is developed for predicting the bioactivity of query drug candidates. As an example, the MF-3D-QSAR is applied to the design of neuraminidase inhibitor and to prove its predictive power, and some useful findings are obtained for developing drugs against influenza virus.
A rapid and efficient method to perform site-directed mutagenesis based on an improved version of overlap extension by polymerase chain reaction (OE-PCR) is demonstrated in this paper. For this method, which we name modified (M)OE-PCR, there are five steps: (1) synthesis of individual DNA fragments of interest (with average 20-bp overlap between adjacent fragments) by PCR with high-fidelity pfu DNA polymerase, (2) double-mixing (every two adjacent fragments are mixed to implement OE-PCR without primers), (3) pre-extension (the teams above are mixed to obtain full-length reassembled DNA by OE-PCR without primers), (4) synthesis of the entire DNA of interest by PCR with outermost primers and template DNA from step 3, (5) post-extension (ten cycles of PCR at 72 degrees C for annealing and extension are implemented). The method is rapid, simple and error-free. It provides an efficient choice, especially for multiple-site mutagenesis of DNAs; and it can theoretically be applied to the modification of any DNA fragment. Using the MOE-PCR method, we have successfully obtained a modified sam1 gene with eight rare codons optimized simultaneously.
A new open reading frame in Thermobifida fusca sequenced genome was identified to encode a new trehalose synthase, annotated as "glycosidase" in the GenBank database, by bioinformatics searching and experimental validation. The gene had a length of 1830 bp with about 65% GC content and encoded for a new trehalose synthase with 610 amino acids and deduced molecular weight of 66 kD. The high GC content seemed not to affect its good expression in E. coli BL21 in which the target protein could account for as high as 15% of the total cell proteins. The recombinant enzyme showed its optimal activities at 25 °C and pH 6.5 when it converted substrate maltose into trehalose. However it would divert a high proportion of its substrate into glucose when the temperature was increased to 37 °C, or when the enzyme concentration was high Its activity was not inhibited by 5 mM heavy metals such as Cu but affected by high concentration of glucose. Blasting against the database indicated that amino acid sequence of this protein had maximal 69% homology with the known trehalose synthases, and two highly conserved segments of the protein sequence were identified and their possible linkage with functions was discussed.
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