![]() Phi and psi involve atoms in the segment for which the angles are being measured (seg), the previous segment (seg - 1), and the next segment (seg + 1).įor phi, the four points are the locations of the carboxyl carbon (seg - 1), the amino nitrogen (seg), the alpha carbon (seg), and the carboxyl carbon (seg).įor psi, the four points are the locations of the amino nitrogen (seg + 1), the carboxyl carbon (seg), the alpha carbon (seg), and the amino nitrogen (seg). This allows phi and psi (and dihedral angles in general) to be specified by just four points. The planes for phi and psi both share two atoms with the reference plane. Phi involves the four atoms on the left psi involves the four atoms on the right. The component atoms that determine phi and psi. Psi is the angle between this plane and the reference plane. The plane for psi contains the amino nitrogen from the next segment, plus carboxyl carbon and the alpha carbon from the segment in question. Phi is the angle between this plane and the reference plane. The plane for phi contains the carboxyl carbon from the previous segment, plus the amino nitrogen and the alpha carbon from the segment in question. (The carboxyl carbon is sometimes indicated as C' or "C prime".) The reference plane for both phi and psi contains three atoms: the nitrogen in the amino group, the alpha carbon, and the carbon in the carboxyl group. Unlike phi and psi, which are shown in the Rama map, Foldit doesn't have a direct display of omega angles. The peptide bond is expected to be nearly "planar" or flat, so this angle is considered less interesting. The other backbone angle is omega (ω), which involves the peptide bond between two segments. Phi is the horizontal x-axis, psi is the vertical y-axis of the Rama map.īoth phi and psi involve the alpha carbon (or Cα), the atom that connects the sidechain, the amino group, and the carboxyl group, making it the center of a segment's backbone. These angles are plotted on the Rama map. The most important backbone angles are phi (φ) and psi (ψ). They're also referred to as torsion angles, referring to how part of the backbone rotates or twists twists with regard to another part. Generated from Psi and Phi angles at īackbone angles in a protein are dihedral angles, which are the angles between two intersecting planes. In this line view with hydrogens displayed, the sidechain of an isoleucine points down from the point of the yellow triangle. Psi is measured between the purple and the yellow triangles. Phi is measured between the orange and yellow triangles. The yellow triangle is the reference plane.
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