Sahariah, B; Sarma, B. K.* J. Phys. Chem. B. 2021,125, 49, 13394-13405.
The polyproline II (PPII) regions of proteins are important for protein-protein and protein-nucleic acid interactions. In addition, the individual strands of collagen, the most abundant protein in mammals, exist in the PPII helical conformation. However, unlike α-helices and β-sheets, the origin of the PPII helical stability is not clearly understood. Herein, we discovered several backbone noncovalent interactions that can explain the stabilization of the PPII helical conformation. At the centre of the cover art, these interactions are highlighted in a PPII helix. One of these interactions is the well-studied carbonyl-carbonyl (CO···CO) interaction. In the PPII helices, the CO···CO interactions form a unique pattern with an almost linear Oi···Ci+1···Oi+2 angle among three neighboring CO groups, which could be an important structural parameter when considered together with the φ and ψ torsion angles to identify and assign the PPII helical regions of proteins.
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