Structure Analysis of Thymidylate Synthase Gene from LCDV-C

Thymidylate Synthase (TS) is an enzyme involved in making one of the major building blocks for DNA deoxythymidylic acid (dTMP), and plays a critical role in cell growth and division and is overexpressed in the majority of cancers. Lymphocystis disease virus (LCDV) belong to iridoviridae, and the causative agent of lymphocystis disease, which has been reported to occur in over 100 different fish species worldwide, and viral infection that causes cells to become megaloblastic, thus forming small tumors (bumps or growths). The complete nucleotide sequence of the LCDV-C genome was recently determined. Among the sequenced vertebrate iridoviruses, lymphocystis disease virus isolated from China (LCDV-C) is of the largest genome. Computer-assisted analysis revealed the potential open reading frames ORF 011L of LCDV-C was TS gene, the first report of complete TS gene from vertebrate iridoviruses. The LCDV-C TS gene consists of 858 bp in length with a base composition of 28.2% G+C, and encoded a protein of 286 amino acids with a predicted size of 32.7KD. Comparison of the LCDV-C TS to TS from Chilo iridescent virus(CIV), Ambystoma tigrinum virus (ATV) and tiger frog virus (TFV) three iridoviruses and other sixteen species, showed extensive amino acid similarities of TS between four iridoviruses and other species. The predicted LCDV-C TS amino acid sequences contain the folate-binding site in 44-70 residues and dUMP-binding site in 163-206 residues. The secondary structure of LCDV-C TS was predicted with 8 alpha helixes, 6 beta sheets and 23 loops, showed the structure flexible and torsional rotation. Phylogenetic tree was constructed based on the multiple alignments of TS amino acid sequences from twenty species, and LCDV-C TS is a branch alone.