オリゴペプチド結晶中の2次構造

概要

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Many oligopeptides with two or more peptide units fold into the so-called secondary structures, which give several rules and accurate parameters of protein foldings. β-turn: Type I is frequently found in the oligopeptides having three or more peptide units. The NCαC angles at the second site are 113-116°. The mean length of the intramolecular 4→1 hydrogen bonds is 3.03Å. Val and Ile having two Cγ atoms are not usually accomodated at the third site. β-sheet structure: Several peptides show the (ideally) parallel β-sheet structures, while at present only tri (L-Ala) crystallizes in an infinitely extended antiparallel β-sheet structure. In some peptide crystals two molecules are linked to a dimer by a pair of hydrogen bonds of the antiparallel β-structure type. Several peptides crystallize in “twisted” β-sheets, and their conformational angles are close to those of the collagen group peptides. poly (L-proline) II helix: Tri- and tetra-prolines are in a poly (L-proline) II helix with the trans peptide bonds. Several others containing Pro and Gly have similar conformations. Cis peptide bond: Cis prolines have been found in Z-GIy-Pro-Leu and a few cyclic oligopeptides. The bond angles around the N atom are : CNCα (cis) = CNCδ (trans) =126°, CNCδ (cis) =CNCα (traps) =121°, and CαNCγ (trans, cis) =113°.
日本結晶学会の論文