Dissection of Factors Affecting the Variability of the Peptide Bond Geometry and Planarity

Figure 4

Local steric hindrance in β-branched residues. Ball-and-stick representations of the most populated rotamer of Val (used here as a representative model of a β-branched residue) are reported. (a) The backbone-independent repulsive interactions between the two heavy C^γ atoms and both backbone N and C atoms are shown as dashed gray lines; they can explain the widening of the NC^αC^β and C^βC^αC angles (the C^β atom is shown in green). (b) The backbone-dependent contact between C^γ1 atom and the O backbone atom is shown (dashed gray lines) in the α-helical conformation (φ, ψ) = (−63°, −43°). (c) In β-sheet conformation (φ, ψ) = (−120°, 130°), the same atoms are on opposite sides. In both panels (b) and (c), the H atoms are omitted for clarity.

(a)

(b)

(c)