Parallel and antiparallel aggregation of α helices

Karle, I. L. ; Flippen-Anderson, J. L. ; Sukumar, M. ; Balaram, P. (1990) Parallel and antiparallel aggregation of α helices International Journal of Peptide and Protein Research, 35 (6). pp. 518-526. ISSN 0367-8377

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An apolar helical decapeptide with different end groups, Boc- or Ac-, crystallizes in a completely parallel fashion for the Boc-analog and in an antiparallel fashion for the Ac-analog. In both crystals, the packing motif consists of rows of parallel molecules. In the Boc-crystals, adjacent rows assemble with the helix axes pointed in the same direction. In the Ac-crystals, adjacent rows assemble with the helix axes pointed in opposite directions. The conformations of the molecules in both crystals are quite similar, predominantly α helical, except for the tryptophanyl side chain where Χ1≃ 60° in the Boc- analog and ≃ 180° in the Ac-analog. As a result, there is one lateral hydrogen bond between helices, N(lε)...O(7), in the Ac-analog. The structures do not provide a ready rationalization of packing preference in terms of side-chain interactions and do not support a major role for helix dipole interactions in determining helix orientation in crystals. The crystal parameters are as follow. Boc-analog: C3H7,N11O13 C3H7OH, space group P1 with a = 10.250(3) Å, b = 12.451(4) Å, c = 15.077(6)Å, x= 96.55(3)°, β = 92.31(3)°, y= 106.37(3)°,, Z = 1, R = 5.5% for 5581 data (|F| > 3.0a(F)), resolution 0.89 Å. Ac-analog: C57,H91,N11,O12, space group P21, with a = 9.965(1) Å, b = 19.707(3) Å, c = 16.648(3) Å, β= 94.08(1), Z = 2, R = 7.2% for 2530 data (|F| > 3.0σ(F)), resolution 1.00 Å.

Item Type:Article
Source:Copyright of this article belongs to Munksgaard International Publishers.
Keywords:Z-helix and Mixed 310/α -helix;head-to-tail Hydrogen Bonding; Hydrogen Bonds; Hydrophobic Attractions; Ile Conformations; Polymorphs; X-ray Diffraction
ID Code:91388
Deposited On:21 May 2012 08:41
Last Modified:21 May 2012 08:41

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