Optimization of a β-sheet-cap for long loop closure

Area of Science:

• Biochemistry and Molecular Biology
• Structural Biology
• Biophysics

Background:

• Protein loops are crucial for secondary structure but their dynamics and stability effects remain poorly understood.
• Investigating loop closure dynamics and composition effects on fold stability is essential for understanding protein folding.
• Existing methods offer limited insight into the stability and dynamics of these critical protein elements.

Purpose of the Study:

• To design and characterize novel peptide systems for studying protein loop dynamics and fold stability.
• To investigate the impact of loop length and composition on the stability of beta-sheet structures.
• To utilize tryptophan (Trp) pairs as spectroscopic probes for assessing stability and dynamics.

Main Methods:

• Design of peptide sequences with varying loop lengths and compositions connecting two beta-strands.
• Incorporation of paired Trp residues to form stabilizing aromatic clusters.
• Utilizing Nuclear Magnetic Resonance (NMR) and Circular Dichroism (CD) spectroscopy for stability and dynamics analysis.

Main Results:

• A 16-residue loop peptide system demonstrated measurable folding stability (ΔG_U = 1.6 kJ/mol).
• Addition of a Trp/Trp pair significantly enhanced beta-sheet stability in a 16-residue loop peptide (ΔG_U = 6.3 kJ/mol, T_m ≈ 55°C).
• Trp/Trp pairs proved effective as spectroscopic probes for stability and dynamics via NMR.

Conclusions:

• Engineered peptide constructs with Trp pairs offer a powerful platform for studying protein loop effects.
• The findings provide new insights into the relationship between loop composition, stability, and folding dynamics.
• These systems serve as valuable tools for peptide chemists and structural biologists.