Solution dimensions of the gramicidin dimer by dynamic light scattering

Area of Science:

• Biophysics
• Biochemistry
• Physical Chemistry

Background:

• Gramicidin is a peptide antibiotic known to form helical structures.
• Previous studies suggest gramicidin forms dimeric rods in alcohol solutions.
• Evidence indicates that potassium ions may alter gramicidin's rod dimensions.

Purpose of the Study:

• To investigate the solution structure of gramicidin in alcohol solvents.
• To determine the effect of potassium ions on gramicidin's dimensions.
• To calculate translational and rotational diffusion coefficients to infer solution dimensions.

Main Methods:

• Diffusion coefficient measurements of gramicidin in methanol and ethanol.
• Addition of potassium thiocyanate (KSCN) to observe ion effects.
• Calculation of solution dimensions from diffusion data.

Main Results:

• Gramicidin exists primarily as dimers in methanol and ethanol solutions.
• The addition of potassium ions leads to a decrease in the length of the gramicidin rod.
• Diffusion coefficients were determined in the presence and absence of KSCN.

Conclusions:

• Gramicidin predominantly forms dimeric helical rods in alcohol solutions.
• Potassium ions induce a conformational change, shortening the gramicidin rod.
• Findings align with X-ray crystallographic data on gramicidin.