Figure 3.

Extension of the Tyr side chain out of the membrane in different rotamers. The distance the Tyr Oη atom extends out of the membrane core depends on the Tyr χ1 angle. The Oη atom extends 5.0 Å toward the C-terminal side of the membrane with χ1 = 180°, but it only extends 3.2 Å and 2.0 Å toward the N-terminal side with χ1 = +60° and −60°, respectively. These distances are the extension of the Oη atom from the Cβ along the membrane normal. For each χ1 angle, we averaged the distances of Tyr placed in eight different positions in β-strands. These values are specific to lipid-facing Tyr residues. Residues facing inside the β-barrel have a different angle between the N-Cα bond and the normal membrane, and therefore the χ1 angles affect the Oη extension differently.