Stabilization of a type VI turn in a family of linear peptides in water solution

摘要: The sources of the stability a type VI turn formed with high population in cis isomeric form an unblocked six residue peptide, Ser1-Tyr2-Pro3-Tyr4-Asp5-Val6 (SYPYDV), were investigated by making extensive amino acid substitutions at residues 2, 4 and 5. Several NMR parameters indicate presence turn, including significant upfield shifts proton resonances proline, small 3JHN alpha coupling constant for cross-turn d N(i,i+2) from 2 to increased mole fraction conformational ensemble. By these criteria, number peptides found contain populations conformers peptide. are highly dependent on sequence strongly correlated each other turn. greatest conformations observed general AA-Ar-Pro-Ar-Hp, where AA represents any acid, Ar aromatic Hp hydrophilic residue. There is no evidence lowered amide temperature coefficients direct hydrogen bonding as primary source stability. Instead, major stabilizing factor, indicated strong dependence (not hydrophobic) positions 4, stacking proline rings. A measurable preference deprotonated aspartate position 5, which not part itself, destabilization low pH, that electrostatic interactions between N terminus carboxyl group also act stabilize conformation when Ar-Pro-Ar present. Implications stabilization local elements secondary structure during earliest events protein folding discussed.