alpha- and 3(10)-helix interconversion: a quantum-chemical study on polyalanine systems in the gas phase and in aqueous solvent.
Helices are among the predominant secondary structures in globular proteins. About 90% of the residues in them are found to be in the alpha-helical conformation, and another 10% in the 3(10) conformation. There is a standing controversy between experimental and some theoretical results, and controversy among theoretical results concerning the predominance of each conformation, in particular, helices. We address this controversy by ab initio Hartree-Fock and density functional theory studies of helices with different lengths in a vacuum and in the aqueous phase. Our results show that (1) in a vacuum, all oligo(Ala) helices of 4-10 residues adopt the 3(10) - conformation; (2) in aqueous solution, the 6-10 residue peptides adopt the alpha-helical conformation; (3) there might be two intermediates between these helical conformers allowing for their interconversion. The relevance of these results to the structure and folding of proteins is discussed.
Topol
I A
IA
Advanced Biomedical Computing Center, SAIC Frederick, P.O. Box B, National Cancer Institute at Frederick, Frederick, Maryland 21702-1201, USA. topol@ncifcrf.gov
Burt
S K
SK
Deretey
E
E
Tang
T H
TH
Perczel
A
A
Rashin
A
A
Csizmadia
I G
IG
D006860:Hydrogen Bonding; D008958:Models, Molecular; D010455:Peptides / Q000737:chemistry*; D017433:Protein Structure, Secondary; D011506:Proteins / Q000737:chemistry*; D011789:Quantum Theory; D012997:Solvents; D014867:Water
D010455:Peptides; D011506:Proteins; D012997:Solvents; D014867:Water; C019529:polyalanine