Fig. 2: PPII helix assembly orientations.
From: Orientation affects hydrogen bonding cooperativity in polyproline II helical bundles
A 2D, Gly-rich antiparallel PPII helical bundle computational model: red spheres represent oxygen; blue, nitrogen; gray, carbon, and white, hydrogen. B Graphical representation of a PPII helix as a triangle and of the three-fold symmetry axis as a dashed line. C Graphical side-view representation of the 3D, Gly-rich PDPR configuration. D Graphical side-view representation of the 3D, Gly-rich PDAR configuration. E Graphical side-view representation of the 3D, Gly-rich ADPR configuration. F Graphical side-view representation of the 3D, Gly-rich ADAR configuration. The gray PPII helices are parallel to each other and the yellow PPII helices are parallel to each other, so the yellow and gray helices are antiparallel to each other. PDPR: parallel PPII helices along both the direct growth direction (from the carbonyl oxygen of B and the reverse (from the amide hydrogen of B); PDAR: parallel PPII helices along the direct growth direction and antiparallel along the reverse; ADPR: antiparallel PPII helices along the direct growth direction and parallel along the reverse, and ADAR: antiparallel PPII helices along both the direct and the reverse growth directions.
