Hydrophobicity-induced pK shifts in elastin protein-based polymers

Area of Science:

• Biopolymers
• Materials Science
• Physical Chemistry

Background:

• Elastin-based polypentapeptides are model systems for studying protein conformational changes.
• Hydrophobicity plays a crucial role in the inverse temperature transition and folding of these peptides.
• Understanding residue-level interactions is key to controlling peptide behavior.

Purpose of the Study:

• To investigate how changes in hydrophobicity affect the pKa and its temperature dependence of glutamic acid residues in elastin-like polypentapeptides.
• To synthesize and characterize novel polypentapeptide analogues with modified hydrophobic residues (Ile and Phe).
• To elucidate the relationship between hydrophobicity, molecular proximity, and acid-base properties.

Main Methods:

• Synthesis of three elastin-like polypentapeptide analogues with varying hydrophobic residues (Val, Ile, Phe).
• Measurement of pKa values and their temperature dependence for the glutamic acid residues.
• Analysis of structural changes and residue proximity using spectroscopic and physical chemistry techniques.

Main Results:

• Significant pKa shifts (up to 1.7 units) were observed upon increasing hydrophobicity.
• A steeper temperature dependence of pKa was noted for more hydrophobic analogues, linked to residue proximity.
• The addition of 0.15 N NaCl suppressed the hydrophobicity-induced pKa shift, despite the dominance of inverse temperature transitions.

Conclusions:

• Hydrophobicity is a critical determinant of the acid-base properties of glutamic acid residues in elastin-like polypentapeptides.
• The proximity of hydrophobic residues to glutamic acid influences pKa and its temperature sensitivity.
• Salt concentration can modulate hydrophobicity-driven effects on peptide ionization.