Fig. 2: Structural details of the gateway/annulus complex.
A, B The backbone of the gateway (magenta). A The basic (blue, stick) and acidic (red, stick) amino acid residues of the gateway (residues 564–592, magenta) from the ABCA1 structure determined by cryo-EM13. The three amino acid residues in the gateway known to be mutated in Tangier disease (four point mutations in total) are shown in the space-filling mode. B The POPC molecule (yellow stick) forms salt-bridges to residues D571 and K568 (space-filling red and blue, respectively) in the 1.9 µsec frame during coarse-grained molecular dynamics (CGMD) modeling of unmutated ABCA1. All side chains but residues D571 and K568 are magenta stick. C The gateway (magenta)/annulus (cyan) complex. Residues of the elongated hydrophobic tunnel that lie within 10 Å of any gateway residue form the annulus domain (residues 69, 71–80, 363, and 368–379). D The annulus (cyan) viewed from the side opposite the outward-facing transmembrane cavity. Note the small orifice (residues 73-75, 77, 78, 371, 375, colored white) in the middle of the annulus through which magenta-colored residues of the gateway on the opposite side are visible. E The base of the annulus (D) rotated 180° around the y-axis to show the gateway. The view is from the outward-facing transmembrane cavity. F Representation of the annulus with the gateway removed to display the annulus orifice. G The amino acid composition of the gateway/annulus complex. Acidic residues, rose; basic residues, blue; aromatic residues, magenta; hydrophobic residues, orange; prolines, yellow; neutral residues, green; glycines, white.
