Parallel β-Sheet Structure and Structural Heterogeneity Detected within Q11 Self-Assembling Peptide Nanofibers.

Area of Science:

• Biomaterials Science
• Molecular Biophysics
• Peptide Self-Assembly

Background:

• Q11 peptide nanofibers are biomaterials for antigen presentation and tissue engineering.
• Previous knowledge of their molecular-level structure was limited.
• The Q11 sequence was designed for antiparallel β-sheet formation using hydrophobic/polar amino acid patterning.

Purpose of the Study:

• To investigate the molecular organization of self-assembled Q11 peptide nanofibers.
• To determine if the molecular structure aligns with the design's expectation of antiparallel β-sheets.
• To evaluate the effectiveness of heuristics-based design in controlling peptide assembly.

Main Methods:

• Solid-state nuclear magnetic resonance (NMR) spectroscopy was the primary technique.
• Two-dimensional (2D) ¹³C-¹³C dipolar-assisted rotational resonance (DARR) was used to assess spatial proximity.
• Frequency-selective rotational echo double resonance (fsREDOR) and ¹³C PITHIRDS-CT dipolar recoupling were employed to analyze β-sheet arrangements.

Main Results:

• Q11 nanofibers exhibit structural heterogeneity, forming a distribution of molecular structures.
• Contrary to design, the predominant structure consists of parallel β-sheets, not antiparallel.
• Approximately 9% of residues (K3 and E9) showed proximity indicative of salt bridge formation, and 22% of β-strands had antiparallel neighbors.

Conclusions:

• Heuristics-based design can promote β-sheet formation but struggles with precise control over β-strand arrangement.
• Solid-state NMR revealed unexpected parallel β-sheet assembly in Q11 nanofibers.
• Designing specific peptide self-assembly structures remains a significant challenge.