Essenz der Empirischen Chou-Fasman-Regeln:
1. A cluster of four helical residues (H_α or h_α) out of six residues along the protein sequence will nucleate a helix, with weak helical residues (I_α) counting as 0.5 h_α. The helical segment is extended in both directions until α-tetrapeptide breakers with {P_α} < 1.00 are reached. Pro cannot occur in the inner helix or at the C-terminal helical end. Pro, Asp, Glu and His, Lys, Arg are incorporated, respectively, at the N- and C-terminal ends. Any segment with {P_α} >= 1.03 as well as {P_α} > {P_β} is predicted as helical.
2. A cluster of three β formers (H_β or h_β) out of five residues along the protein sequence will nucleate a β-sheet. The β-sheet is extended in both directions until β-tetrapeptide breakers with {P_β} < 1.00 are reached. Any segment with {P_β} >= 1.05 as well as {P_β} > {P_α} is predicted as β-sheet.
3. When regions in proteins contain both α- and β-forming residues, the overlapping region is helical if {P_α} > {P_β}, or β-sheet if {P_β} > {P_α}.
4. The probability of bend occurence at residue i is calculated from p_t = f_i x f_i+1 x f_i+2 x f_i+3 with the aid of a Table of the conformational parameters for β-turn formation. The average probability of β-turn occurence is {p_t} = 0.55 x 10^-4. Tetrapeptides with p_t > 0.75 x 10^-4 as well as {P_t} > 1.00 and {P_α} < {P_t} > {P_β} are selected as probable bends.

Referenzen:

• P.Y. Chou and G.D. Fasman (1978)
  Empirical predictions of protein conformation
  Annu. Rev. Biochem. 47: 251-276

Latest update of content: June 12, 2002

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