Peptide models. XIV. Ab initio study on the role of side-chain backbone interaction stabilizing the building unit of right- and left-handed helices in peptides and proteins
✍ Scribed by András Perczel; Ödön Farkas; John F. Marcoccia; Imre G. Csizmadia
- Publisher
- John Wiley and Sons
- Year
- 1997
- Tongue
- English
- Weight
- 407 KB
- Volume
- 61
- Category
- Article
- ISSN
- 0020-7608
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✦ Synopsis
Previous ab initio computations revealed that the conformational building unit of the Ž . right-handed helix f y54Њ, f y45Њ is not an energy minimum on two-Ž Ä 4 . dimensional-type Ramachandran potential energy surfaces E s E , . Theoretical investigations were performed on several single-amino-acid diamides such as For᎐Gly᎐NH , For᎐L᎐Ala᎐NH , Ac᎐L᎐Ala᎐NHMe, and For᎐L᎐Val᎐NH containing 2 2 2 Ž . amino acid residues e.g., Ala which can often be found in helices as shown by X-ray w Ž .x data analysis of globular proteins. The current ab initio self-consistent field SCF Ž w U U x . results based on four different basis sets 3-21G, 4-21G, 4-21G , and 6-31G presented Ž . point toward an intrinsic i.e., non-environmental-assisted stability of the right-handed helical subconformation of a simple amino acid diamide if the residue contains a polar side chain. Such is the case for a serine derivative when its ᎏCH OH side chain is 2 favorably oriented. For the For᎐L᎐Ser᎐NH model compound two slightly different 2 right-handed helical backbone conformations were determined. Depending on the relative Ž orientation of the side chain, the conformational monomer of the 3 helix a sharper 10 & Sons, Inc.