As described in [37, 71] , the conversed H-bonding network formed by the polar acidic head of Core A in both GW409544 and Comp#1 to the four key residues of PPARa (or PPARc), such as Ser280 (or Ser289), Tyr314 (or His323), Tyr464 (or Tyr473) and His440 (or His449), were observed in our docking study. This Hbonding network played the role in stabilizing the conformation of the AF2-helix in arm I (red helix in Fig. 1) , which is vitally important for receptor-binding and activation [37, 72, 73, 74, 75, 76, 77] .