High-resolution structure and dynamic implications for a double-helical gramicidin A conformer

Area of Science:

• Structural Biology
• Biophysics
• Molecular Biophysics

Background:

• Gramicidin A is a channel-forming polypeptide known for its biological activity.
• Understanding its precise structure is key to elucidating its membrane interaction mechanisms.

Purpose of the Study:

• To determine the high-resolution three-dimensional structure of a dimeric conformer of gramicidin A.
• To investigate the structural basis for gramicidin A's channel-forming properties.

Main Methods:

• Two-dimensional Nuclear Magnetic Resonance (2D NMR) techniques were employed in a benzene-ethanol mixed-solvent system.
• Experimental constraints, including Nuclear Overhauser Effects (NOEs) and coupling constants, were used for structure determination.
• Distance geometry and simulated annealing routines were utilized for structure refinement and side-chain conformation analysis.

Main Results:

• The high-resolution structure of a gramicidin A dimer was elucidated, revealing an antiparallel intertwined double helix.
• The determined structure features approximately 5.6-5.7 residues per turn, a dimer length of 36-37 Å, and a pore width of 2.5-3.0 Å.
• Side-chain conformations were analyzed, showing substantial amphipathic character that may influence membrane insertion.

Conclusions:

• The determined structure provides critical insights into the molecular architecture of gramicidin A dimers.
• The amphipathic nature of the side chains is proposed to play a significant role in the conformational changes associated with membrane insertion.
• This structural information is vital for understanding the mechanism of ion channel formation by gramicidin A.