Energy of stabilization of the right-handed beta alpha beta crossover in proteins.
An explanation in terms of conformational energies is provided for the observed nearly exclusive preference of the beta alpha beta structure for forming a right-handed, rather than a left-handed, crossover connection. Conformational energy computations have been carried out on a model beta alpha beta structure, consisting of two six-residue Val beta-strands and of a 12-residue Ala alpha-helix, connected by two flexible four-residue Ala links to the strands. The energy of the most favorable right-handed crossover is 15.51 kcal/mol lower than that of the corresponding left-handed cross-over. The right-handed crossover is a strain-free structure. Its energy of stabilization arises largely from the interactions of the two beta-strands with one another and with the alpha-helix. On the other hand, the left-handed crossover is either disrupted after energy minimization or it remains conformationally strained, as indicated by an energetically unfavorable left twisting of the beta-sheet and by the presence of high-energy local residue conformations. In the energetically most favorable right-handed crossover, the right twisting of the beta-sheet and its manner of interacting with the alpha-helix are identical with those computed earlier for isolated beta-sheets and for packed alpha/beta structures. This result supports a proposed principle that it is possible to account for the main features of frequently occurring structural arrangements in globular proteins in terms of the properties of their component structural elements.
Chou
K C
KC
Computational Chemistry Unit, The Upjohn Company, Kalamazoo, MI 49001.
Némethy
G
G
Pottle
M
M
Scheraga
H A
HA
D004734:Energy Metabolism; D008958:Models, Molecular; D010455:Peptides; D011487:Protein Conformation; D011506:Proteins / Q000378:metabolism
D010455:Peptides; D011506:Proteins