TPP binding site of the model structure of TtALS.

TtALS_WT, TtALS_H474R, and the neighboring monomer are shown in gray, purple, and cyan, respectively. TPP and FAD are shown in yellow, whereas Mg²⁺ is represented as a yellow sphere. Oxygen atoms are shown in red whereas nitrogen atoms are in blue. New hydrogen bonds are formed between the side chain of H474R with the side chain of S479 and the main chain of M28, which belongs to the neighboring monomer (shown by dotted lines). The cavity through which substrates seem to access the catalytic site is indicated by a black arrow.