Give two reasons to explain why a proline residue in the middle of an α-helix is predicted to be destabilizing to the helical structure. Check all tha apply. A. Pro does not have the α−NH group that acts as a stabilizing H-bond donor in the middle of the helix. B. Pro is nonpolar amino acid that does not connect turns of the α-helix. C. Pro is nonpolar amino acid that destabilizes polar core of the protein. D.Insertion of Pro gives an exceptional conformational rigidity to the protein chain chain. E. Pro is not able to adopt the ideal ϕ and ψ angles for an α -helix.