Helix-forming tendencies of amino acids in short (hydroxybutyl)-L-glutamine peptides: an evaluation of the contradictory results from host-guest studies and short alanine-based peptides.
The helix propensities ("s-values") of amino acids measured using short alanine-based peptides are different, in both magnitude and rank order, from those found using random sequence copolymers of a "guest" amino acid and a (hydroxyalkyl)-L-glutamine "host". The origin of these differences is investigated here. In short alanine-based peptides containing 1-5 (hydroxybutyl)-, (hydroxypropyl)-, or (hydroxyethyl)-L-glutamines (HBQ, HPQ, and HEQ, respectively), we find the rank order of helix propensities to be Ala > HBQ > HPQ > HEQ, which is consistent with earlier results for HBQ, HPQ, and HEQ homopolymers and is attributed to helix-stabilizing hydrophobic interactions [Lotan, N., Yaron, A., & Berger, A. (1966) Biopolymers 4, 365-368]. The apparent s-values of nonpolar amino acids in a 17-residue, HBQ-based peptide cluster around 1, as they do in the host-guest studies, but in contrast to results with alanine-based peptides. The differences between the host-guest results and results obtained using alanine-based peptides may be rationalized in terms of side-chain interactions involving the hydroxyalkyl moiety.
Padmanabhan
S
S
Department of Biochemistry, Stanford University School of Medicine, California 94305.
York
E J
EJ
Gera
L
L
Stewart
J M
JM
Baldwin
R L
RL
D000409:Alanine / Q000737:chemistry*; D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry*; D002942:Circular Dichroism; D005973:Glutamine / Q000031:analogs & derivatives* / Q000737:chemistry; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry*; D017433:Protein Structure, Secondary; D013329:Structure-Activity Relationship; D014443:Tyrosine / Q000737:chemistry
D000596:Amino Acids; D010455:Peptides; C010985:hydroxybutylglutamine; D005973:Glutamine; D014443:Tyrosine; D000409:Alanine