FIG. 5.

Flavin site of A. fulgidus ISF3. In contrast to ISF-Mt, access to this site is limited due to the side chain of Arg99 from a neighboring monomer. Stacked between the flavin and a cation-π interaction with the side chain of Arg102, a benzamidine molecule (BAM) from the crystallization buffer was modeled hydrogen bonded to Arg99. The aromatic ring of the benzamidine molecule is situated in a hydrophobic pocket created by Leu121 and Phe84. The benzamidine sits at the entrance of a channel that crosses the entire ISF3 tetramer (see Fig. 6).