Amino acid, that destabilizes alpha-helix is:
Proline lacks an amide proton, this precludes hydrogen bonding between it and hydrogen bond acceptors, and thus often restricts the residue to the first four positions of an a-helix. Helices with proline after position four have a pronounced kink. a -helix: It is a spiral structure resulting from hydrogen bonding between one peptide bond and the fouh one. Stability of an a helix: The stability of an a helix arises primarily from hydrogen bonds formed between the oxygen of the peptide bond carbonyl and the hydrogen atom of the peptide bond nitrogen of the fouh residue down the polypeptide chain. The ability to form the maximum number of hydrogen bonds, supplemented by van der Waals interactions in the core of this tightly packed structure, provides the thermodynamic driving force for the formation of an a helix. Proline: The peptide bond nitrogen of proline lacks a hydrogen atom to contribute to a hydrogen bond, proline can only be stably accommodated within the first turn of an a helix. When present elsewhere, proline disrupts the conformation of the helix, producing a bend. Glycine also tends to disrupt helices because its high conformational flexibility makes it entropically expensive to adopt the relatively constrained a-helical structure. Ref: Molecular Biology: Genes to Proteins, By Buon E. Tropp,4th Edition, Page 53.
Proline
Alanine
Glutamine
Tryptophan