Position of Lys300 on TM 10. (A) Cartoon representation of the structure viewed from the periplasmic side of the membrane. The charged residues, Asp133 (TM 4b), Asp163 (TM 5) and Asp164 (TM 5), and Lys300 (TM 10), in the new structure are shown as colored sticks. The position of Lys300 in the previously published structure (Protein Data Bank accession no. 1ZCD) is shown in gray (red text). The structure has been colored from red at the N terminus through to blue at the C terminus. Loop regions except for the breaks between the discontinuous helices have been omitted for clarity. (B) As A, but from the side and zoomed in. The dashed line represents the salt bridge between Asp163 and Lys300.