Uniformity, ideality, and hydrogen bonds in transmembrane alpha-helices

Area of Science:

• Structural biology
• Biophysics
• Protein science

Background:

• Protein environments critically impact molecular interactions and structural stability.
• Transmembrane helices reside in the hydrophobic lipid bilayer, lacking water and featuring hydrophobic amino acid residues.

Purpose of the Study:

• To analyze the structural uniformity of transmembrane helices.
• To investigate hydrogen bond geometry, peptide plane tilt, and backbone torsion angles in specific transmembrane helices.

Main Methods:

• Analysis of bacteriorhodopsin crystal structures.
• Examination of M2 protein transmembrane helix structures from influenza A.
• Comparison of X-ray crystallography and solid-state Nuclear Magnetic Resonance (NMR) data.

Main Results:

• Certain transmembrane helices display exceptional uniformity in hydrogen bond geometry, peptide plane tilt, and backbone torsion angles.
• Intramolecular backbone hydrogen bonds in these helices are shorter than those in water-soluble proteins.
• Hydrogen bond geometry indicates a dominance of electrostatic over covalent contributions.

Conclusions:

• Transmembrane helices possess a high degree of structural uniformity, influenced by their lipid bilayer environment.
• Electrostatic interactions play a key role in stabilizing the backbone hydrogen bonds of transmembrane helices.
• Increased structural resolution reveals greater helix uniformity, suggesting more such structures may be identified in existing databases.