Figure 3.

Recognition of bile acids by RamR. (a) The substrate-binding site of RamR with bound cholic and chenodeoxycholic acid molecules. Key residues that are involved in forming hydrogen bonds with cholic or chenodeoxycholic acid are shown, including Tyr59, Thr85, Ser137 and Asp152 (indicated by red characters). Objects are colored as in Fig. 2. (b) Close-up view of the substrate-binding site of RamR containing cholic acid or chenodeoxycholic acid. Objects are colored as in Fig. 2, and key residues are colored as in Fig. 2a. Hydrogen bonds are indicated by dotted red lines.