Structure of tyrocidine micelles in isotropic aqueous solution

Area of Science:

• Biophysical Chemistry
• Structural Biology
• Biomolecular Interactions

Background:

• Tyrocidine B is a cyclic peptide antibiotic with known antimicrobial properties.
• Understanding the aggregation behavior of tyrocidine B is crucial for elucidating its mechanism of action and potential therapeutic applications.

Purpose of the Study:

• To characterize the structural and hydrodynamic properties of tyrocidine B aggregates.
• To investigate the effect of iodine labeling on the aggregation process of tyrocidine B.

Main Methods:

• Analytical ultracentrifugation to determine molecular weight and sedimentation behavior.
• Light scattering techniques (inelastic and static) to assess aggregate size and hydrodynamic properties.
• Small-angle X-ray scattering (SAXS) to provide structural information on the aggregates.

Main Results:

• Tyrocidine B, iodoacetyltyrocidine B, and diiodotyrocidine B form aggregates with a molecular weight of 28,600.
• Hydrodynamic analysis describes these aggregates as rods (170 Å length, 30 Å diameter), consistent with SAXS data.
• Light scattering and SAXS yielded comparable hydrodynamic parameters (Stokes radii, frictional ratios) across various concentrations.
• Iodine atoms were localized at a radius of 16 Å, with an iodine-iodine distance of 34 Å across the aggregate cross-section.

Conclusions:

• The rod-like model provides a valid description of tyrocidine B aggregates.
• Iodine labeling does not interfere with the aggregation process of tyrocidine B.
• The applied biophysical techniques are effective in characterizing the structural and hydrodynamic properties of peptide aggregates.