A helix propensity scale based on experimental studies of peptides and proteins.
The average globular protein contains 30% alpha-helix, the most common type of secondary structure. Some amino acids occur more frequently in alpha-helices than others; this tendency is known as helix propensity. Here we derive a helix propensity scale for solvent-exposed residues in the middle positions of alpha-helices. The scale is based on measurements of helix propensity in 11 systems, including both proteins and peptides. Alanine has the highest helix propensity, and, excluding proline, glycine has the lowest, approximately 1 kcal/mol less favorable than alanine. Based on our analysis, the helix propensities of the amino acids are as follows (kcal/mol): Ala = 0, Leu = 0.21, Arg = 0.21, Met = 0.24, Lys = 0.26, Gln = 0.39, Glu = 0.40, Ile = 0.41, Trp = 0.49, Ser = 0.50, Tyr = 0. 53, Phe = 0.54, Val = 0.61, His = 0.61, Asn = 0.65, Thr = 0.66, Cys = 0.68, Asp = 0.69, and Gly = 1.
Pace
C N
CN
Department of Medical Biochemistry and Genetics, Texas A&M University, College Station, Texas 77843-1114, USA. pace@bioch.tamu.edu
Scholtz
J M
JM
D000596:Amino Acids / Q000737:chemistry; D055592:Biophysical Phenomena; D001703:Biophysics; D010455:Peptides / Q000737:chemistry*; D017433:Protein Structure, Secondary; D011506:Proteins / Q000737:chemistry*; D013816:Thermodynamics
D000596:Amino Acids; D010455:Peptides; D011506:Proteins