Figure 5.

Transmembrane assembly including the contribution of sterol lipid

(A) Extracellular view of the transmembrane domain (layer 3).

(B) The two CD3-ζ chains (shown in white) are positioned in very different environments within the CD3 TM assembly. The view is related to Figure 4A by a 165° rotation around the longest axis of the complex. Residues interacting with CD3-ζ (blue) and CD3-ζ′ (cyan) were identified using the program PISA (Krissinel and Henrick, 2007) and are shown as sticks and with their atomic van der Waals radii as transparent spheres.

(C) Tight associations in the outer leaflet portions of the TCR-α and TCR-β TMs with CD3-εδ and CD3-ε′γ, respectively, enable the intra-membrane neutralization of positive charges in TCR-α and TCR-β. Hydrogen bonds and salt bridges in (A) and (C) are depicted by black dashed lines.

(D) Extra non-protein density (transparent blue surface) was observed in the outer leaflet between the TM helices of CD3-ζ′ and CD3-γ, likely matching a cholesterol molecule.