Fig. 1: Natural Proteins with PPII helical bundles.

Experimentally determined structures from PDB for Hypogastrura harveyi AFP short isoform (PDB ID: 3BOG), Salmonella phage S16 tail fiber adhesin Gly-rich domain (PDB ID: 6F45), ALK Gly-rich domain (PDB ID: 7LS0/7LRZ), Aromatoleum aromaticum acetophenone carboxylase Gly-rich domain (PDB ID: 5L9W), Bacillus subtilis Obg GTPase Gly-rich domain (PDB ID: 1LNZ) and Granisotoma ranieri AFP (PDB ID: 7JJV), and predicted structure from Hypogastrura harveyi AFP long isoform (AF2 ID: D7PBP2). Roman numerals denote the distinct helices in each protein. From the reader’s perspective, the yellow PPII helices run from the N-terminus (bottom) to the C-terminus (top) and are parallel to each other; the gray PPII helices run from the C-terminus (bottom) to the N-terminus (top) and are parallel to each other, so the yellow and gray helices are antiparallel to each other.