Fig. 3.

Occupancy of the inner cavity of the c₈-ring. (A) Cross-section of the solvent-excluded surface of the model of the c₈-ring and e-subunit of the membrane domain, the foot of the central stalk, and the unmodeled density (teal), which is mainly the detergent-lipid micelle surrounding the protein, plus density extending beyond residue e58 toward the opening of the central cavity of the c₈-ring. (B) Cross-sectional view of the solvent-excluded surface of the membrane domain. The unmodeled region (khaki transparency) probably represents residues e59 to the C-terminal residue e70. It is conceivable that a brief span of the extreme C-terminal region penetrates a short distance into the cavity of the c₈-ring and that this region is occupied by the C-terminal tail of subunit e plus a phospholipid (PLC). The density inside the c₈-ring is weak and rotationally averaged and probably represents PLC molecules (SI Appendix, Fig. S13). A second PLC is shown occupying the upper region of the cavity.