Fig. 6: Structural determinant for the silicic acid permeability and modeled eight silicic acid positions in the Lsi1 channel.

SF of Lsi1_cryst (a), and a possible conformation of silicic acid during the passage through SF (b). Water molecules in the channel (Wat1, Wat2, Wat3, Wat4, and Wat9) are shown as spheres and numbered in blue. Among them, three (Wat1, Wat2, and Wat4) are superposition from the eight Lsi1_cryst protomers of the two tetramers. Putative hydrogens of hydroxyl groups of the silicic acid in the position Si2 are encircled by dashed lines. The view direction is the same as Fig. 2a. Water molecules used for the assignment of possible silicic acid positions (c) and the assigned eight silicic acids (Si1-Si8) in the channel (d) are shown in a cross-section view. Water molecules in the channel region (red spheres) and the extracellular region (pink spheres) are labeled in numbers. Arg222_LE2 in the SF region and two Asn residues in the NPA motifs are shown as the stick. e Water molecules employed for the assignment of four hydroxyl groups in silicic acid are listed. Ext in c and e indicates water molecules at the extracellular side.