Table 1.

Bond Angles (τ) and Torsional Rotations (ϕ and ψ) about Glycosidic Bonds in the Refined Structures of the PelC–(Ca2+)3–4–PentaGalpA Complexesa

Glycosidic Bondτbϕcψd
31 Helixe117.0°80.0°89.0°
21 Helixf117.0°80.0°161.0°
GalpA1–GalpA2117.0°54.0°90.0°
GalpA2–GalpA3116.6°117.0°157.0°
GalpA3–GalpA4120.4°73.0°51.0°
  • a Torsional angles were determined by looking from the nonreducing end side (with prime) down the bond of interest to the reducing end side and determining the angle of rotation created from the planes of O-5′–C-1 ′–O-4 and C-1′–O-4–C-4 for ϕ and C-1′–O-4–C-4 and O-4–C-4–C-5 for ψ. A cis configuration is taken to be 0°, and a trans configuration is taken to be 180°. A negative sign is a rotation from cis in a counterclockwise direction, and a positive sign is a rotation from cis in a clockwise direction.

  • b τ, the C1–O–C4′ bond angle.

  • c ϕ, the torsional rotation about the C1–O bond.

  • d ψ, the torsional rotation about the O–C4′ bond.

  • e The values for the 31 helix are those determined by the program O (Jones et al., 1991) from the model published by Walkinshaw and Arnott (1981b).

  • f The values for the 21 helix are those determined by the program O for a galacturonic acid model constructed using the parameters for alginic acid by Atkins et al. (1973).