Structural study of TcaR and its complex with salicylic acid form Staphylococcus epidermidis

• Main Authors: Yao-Jen Yeh, 葉耀仁
• Other Authors: Andrew H.-J. Wang
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/18565035381196582515

碩士 === 國立臺灣大學 === 生化科學研究所 === 96 === TcaR is a repressor of ica operon that affects biofilm formation in Staphylococcus epidermidis. Here we describe the crystal structure of the apo form TcaR and TcaR-salicylate-cacodylate complex that are determined at the resolution of 2.3 Å and 2.5 Å, respectively. The structure shows TcaR as a dimer with the winged-helix DNA binding motif. It is important that we find the salicylic acid and cacodylate (containing heavy metal As) which can interact with TcaR. Salicylic acid, which inhibits DNA binding, is a known inactivator for some MarR family proteins and the relationship between cacodylate and TcaR may be the same. We compare the structure of apo form TcaR with complex TcaR, revealing that the mechanism of regulation maybe involves a conformational change in the DNA binding domain. In order to confirm TcaR binds specifically to the ica promoter, we combined purified TcaR with the 184-bp probe representing the sequence of the entire wild-type ica promoter from S. epidermidis RP62A in electrophoretic mobility shift assay (EMSA). The results indicate that TcaR indeed bind to the ica promoter. We further predict three fragments of 33-mer DNA that contain partial palindrome sequence within ica operon, which may interact with TcaR, and perform EMSA experiment to confirm the interaction. A series of EMSA experiments revealed that two TcaR dimers bind to 33-mer probe without cooperativity. In summary, our study advances efforts aimed at identifying the regulation mechanisms and finding out small molecules that could modulate the function of the TcaR protein.