Lab2-Peptides
Proteins = Sum of aminoacids
One amino acid X is equipped with two minimal peptide bonds: The C terminus COOH becomes COCH3, the N terminus NH2 becomes NHCH3. For instance, alanine dipeptide is CH3CONHCH(CH3)CONHCH3 or Ace-Ala-NMe
PES (potential energy surface) of one aminoacid
21 proteinogenic aminoacids
Proteins – the machinery of life
Helices -49 -26 -57 -47 -57 -70
Sheets
Loops and turns
OPLS energy hierarchy of Ace-Ala-Ala-NMe
Conformers of Ace-Ala-Ala-NMe
Dihedral angles of Ace-Ala-Ala-NMe
Alpha-helix or 3.6 helix 13
Dipole momentum destabilizes helix NH3+ COO- Addition of certain aminoacids neutralize dipole momentum
Alpha-helix G (goes up) and H (goes down) of myoglobin (C=O bonds form Christmas tree structure) Alpha-helix breakers: glycine (yellow), proline (green) N (red circle) doesn’t form H bond
γ-turn (C7) Separated by 2 bonds (b) β-turn (C10) Separated by 3 bonds (c) α-turn (C13) Separated by 4 bonds (d) π-turn (C16) Separated by 5 bonds Type I β-turns, (b) type II′ β-turns, (c) type VI β-turns
f y Steric interference Structure Fully extended 180 Antiparallel b-sheet -139 135 Parallel b-sheet -119 113 Right-handed a-helix -57 -47 Left-handed a-helix 60 310 helix -49 -26 p-helix -70 Steric interference
Planarity of peptide bond? Peptide bond rotational energies and angular frequency distribution. The histogram represents the angular frequency distribution of 3.938 proteins. The red points are energies derived from Maxwell-Boltzmann relations. The line is the function A sin2 ω for A = 30 kcal mol-1. (Pauling, Corey) The black and gray points are peptide bond rotational energies for proteins and peptides, respectively, and were derived from Maxwell-Boltzmann relations.