Electrostatic Interactions in Collagen-like Triple-Helical Peptides

Abstract

Collagen-like peptides with potential for ion pair formation were studied to investigate the role of electrostatic interactions in the triple-helix conformation. Three peptides--(POG)10, the EK-containing peptide (POG)4EKG(POG)5, and T3-487, a peptide with 18 residues of type III collagen and a C-terminal (GPO)4 tail--all form stable triple helices in aqueous solution, with melting temperatures of 58, 46, and 26 degrees C, respectively, at neutral pH. The thermal stabilities of these peptides correlate with their imino acid content, which is 66%, 60%, and 41%, respectively. Variation of pH over the range of 1-13 led to 8-9 degrees C changes in the Tm of the EK-containing peptide and peptide T3-487, with the greatest stability seen at pH values where both acidic and basic residues are ionized. Equilibrium ultracentrifugation shows these peptides are largely trimeric at low temperature, with no hexamers or larger aggregates, indicating that the pH-dependent stability arises from intramolecular interaction. Computer modeling indicates both intrachain ion pairs and interchain ion pairs can form and stabilize the triple helix. Studies of the pH dependence of the thermal stability of (POG)10 and the N-terminal acetylated form of T3-487 indicate that repulsion of the three charged N-terminal or C-terminal ends has a destabilizing effect. Taking into account these end effects, the energy contribution of two oppositely charged residues in a triple helix which are sterically capable of participating in ion pairs and backbone hydrogen bonding is 0.5-1 kcal/mol ion pair. It is possible that the stabilizing influence of ion pairs arises indirectly, through elimination of like charge repulsion, formation of ion pairs in the single chain form, or solvent effects.

Elongated fibrillar structure of a streptococcal adhesin assembled by the high-affinity association of α- and PPII-helices

“…A negative change in the heat capacity (ΔC P ) supports the burial of hydrophobic surfaces in the association of the helices. The thermodynamic properties of the enthalpically driven association of the alanine-rich and proline-rich repeats are similar in sign and magnitude as those observed in the formation of triplehelical collagen-like peptides (28), and in the binding of SH3 to short PPII-conforming peptides (29). In the latter case, the enthalpy and entropy changes were of opposite sign from that expected of a primarily hydrophobic interaction.…”

Destabilization of osteogenesis imperfecta collagen-like model peptides correlates with the identity of the residue replacing glycine

“…A set of host-guest model peptides of the form acetyl-(Gly-Pro-Hyp) 3 Gly-Xaa-Yaa-(Gly-Pro-Hyp) 4 -Gly-Gly-amide has been studied extensively in our laboratory. This design embeds a guest triplet Gly-Xaa-Yaa near the middle of a Gly-Pro-Hyp-rich environment and has an acetylated N terminus and amidated C terminus to eliminate interactions between guest triplets and ionized ends (25,26). The host peptide acetyl-(Gly-Pro-Hyp) 8 -Gly-Gly-amide has a T m ϭ 45°C, and all of the more than 40 peptides with different L-amino acids in the Xaa and Yaa positions studied thus far formed stable triple helices with melting temperatures in the 20-45°C range (19)(20)(21)(22)27).…”

Preparation and characterization of monomers to tetramers of a collagen-like domain fromStreptococcus pyogenes

“…This may arise from use of a different method to determine the value. In the present study a first derivative was used, 26 whereas, in other studies, the point on the melting curve at 50% melting was determined. Similar, slight differences between these methods have previously been reported, with the first derivative approach giving values up to 1 C higher.…”