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β‐Alanine containing cyclic peptides with turned structure: The “pseudo type II β‐turn.” VI
Author(s) -
Pavone Vincenzo,
Lombardi Angelina,
Saviano Michele,
Nastri Flavia,
Fattorusso Roberto,
Maglio Ornella,
Isernia Carla,
Paolillo Livio,
Pedone Carlo
Publication year - 1994
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.360341109
Subject(s) - chemistry , conformational isomerism , molecule , monoclinic crystal system , hydrogen bond , peptide , crystallography , stereochemistry , crystal structure , peptide bond , carbodiimide , dichloromethane , methylene , turn (biochemistry) , guanidinium chloride , organic chemistry , biochemistry , enzyme , solvent
In the present paper we describe the synthesis, purification, single crystal x‐ray analysis, and nmr solution characterization, combined with restrained molecular dynamic simulations, of the cyclic hexapeptide cyclo ‐( L ‐Pro‐ L ‐Phe‐β‐Ala) 2 . The peptide was synthesized by classical solution methods and the cyclization of the free hexapeptide was accomplished in good yields in diluted methylene chloride solution using N , N ‐dicyclohexyl‐carbodiimide. The compound crystallizes in the monoclinic space group P2 1 from methanol‐dichloro‐methane solution. The two identical halves of the molecule adopt in the solid state two different conformations. One β‐Ala‐ L ‐Pro peptide bond is trans , while the second is cis . The molecule is present in dimethylsulfoxide d 6 solutions as a mixture of conformational families. One of these corresponds to a C 2 symmetrical molecule with both β‐Ala‐Pro cis peptide bonds, while the second major conformation is very similar to that observed in the solid state. All Pro‐Phe segments, both in the solid state and the symmetrical and unsym‐metrical solution conformations, display ϕ,ψ angles close to that of position i + 1 and i + 2 of type II β‐turns. In addition, the segments preceeded by a trans β‐Ala‐Pro peptide bond are characterized by a typical i ← i + 3 hydrogen bond, which is absent in the conformer containing a cis β‐Ala‐Pro peptide bond. The latter conformation corresponds to a new structural domain we define as the “ pseudo type II β‐turn.” © 1994 John Wiley & Sons, Inc.