Apolar peptide models for conformational heterogeneity, hydration, and packing of polypeptide helices: crystal structure of hepta- and octapeptides containing alpha-aminoisobutyric acid

Proteins. 1990;7(1):62-73. doi: 10.1002/prot.340070107.

Abstract

The crystal structures of two helical peptides Boc-Val-Ala-Leu-Aib-Val-ala-Leu-OMe (VALU-7) and Boc-Val-Ala-Leu-Aib-Val-Ala-Leu-Aib-OMe (VALU-8) have been determined to a resolution of 1.0 and 0.9 A, respectively. Both the seven and eight residue peptides crystallize with two conformers per asymmetric unit. The VALU-8 conformers are completely helical and differ only at the C-terminus by a sign reversal of the phi, psi angles of the last residue. One of the VALU-7 conformers occurs as a normal alpha-helix, whereas in the other, the N(7)--O(3) alpha-type hydrogen bond is ruptured by the entry of a water molecule (W) into the helix, which in turn makes hydrogen bonds N(7)...W = 2.97 A and W...O(3) = 2.77 A. The other side of the water molecule is surrounded by a hydrophobic pocket. These two conformers give a static representation of a step in a possible helix unwinding or folding process. In the VALU-8 crystal the helices aggregate in a parallel mode, whereas the aggregation is anti-parallel in the VALU-7 crystal. The crystal parameters are VALU-7, P2(1), a = 10.203 (3) A, b = 19.744 (6) A, c = 22.561 (6) A, beta = 96.76 degrees, Z = 4, C38H69N7O10.0.5H2O, R = 6.65% for 3674 reflections observed greater than 3 sigma (F); and VALU-8, P2(1), a = 10.593 (4) A, b = 27.57 (6) A, c = 17.745 (5) A, beta = 95.76 (3) degrees, Z = 4, C42H76N8O11.0.25 CH3OH, R = 6.63% for 4701 reflections observed greater than 3 sigma (F).

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Aminoisobutyric Acids*
  • Hydrogen Bonding
  • Models, Biological
  • Molecular Sequence Data
  • Oligopeptides*
  • Peptides*
  • Protein Conformation
  • Water*
  • X-Ray Diffraction

Substances

  • Aminoisobutyric Acids
  • Oligopeptides
  • Peptides
  • Water
  • tert-butyloxycarbonyl-valyl-alanyl-leucyl-2-aminoisobutyryl-valyl-alanyl-leucyl methyl ester
  • t-butyloxycarbonyl-valyl-alanyl-leucyl-2-aminoisobutyryl-valyl-alanyl-leucyl-2-aminoisobutyryl methyl ester