Inhibitor Structures in the SD Binding Niche

Some notable backbone differences can be found between the early X-ray structures ISTD and 2STD obtained at low (pH 4.5, pH 5.1) and those obtained later at neutral pH (7.5-8) (3STD-7STD), which can be attributed to the pH differences. Site-directed mutations (see below) support the assumption that these differences affect the lipophilic inhibitor recognition. 

Superposition of the Ca-atoms of 1STD-7STD and looking at the resulting inhibitor positions gives an impression of the extensions of the active site (Fig. 20.6). 

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