Sequence-specific resonance assignment and secondary structure of (1-71) bacterioopsin

Area of Science:

• Biochemistry
• Structural Biology
• Spectroscopy

Background:

• Bacteriorhodopsin is a light-driven proton pump essential for energy transduction in halophilic archaea.
• Understanding the structure of its fragments aids in elucidating the overall protein mechanism.
• Chymotryptic fragment C2 (residues 1-71) represents a significant portion of the protein.

Purpose of the Study:

• To determine the three-dimensional conformation of chymotryptic fragment C2 of bacteriorhodopsin.
• To assign NMR resonances and identify secondary structural elements within the fragment.

Main Methods:

• Two-dimensional proton nuclear magnetic resonance (2D 1H NMR) spectroscopy was employed.
• Phase-sensitive DQF-COSY, TOCSY, and NOESY techniques were used for resonance assignment.
• Deuteration of leucine residues and measurement of deuterium exchange rates aided spectral analysis and conformational stability assessment.

Main Results:

• Resonances in the 1H NMR spectra of fragment C2 were largely assigned.
• Two distinct right-handed alpha-helical regions were identified: Pro8-Lys30 and Lys41-Leu62.
• The N-terminal segment (Ala2-Gly6) was found to adopt a helical conformation stabilized by three hydrogen bonds.

Conclusions:

• The study successfully elucidated the conformation of bacteriorhodopsin fragment C2 using advanced NMR techniques.
• The identified helical regions contribute to the understanding of bacteriorhodopsin's overall structure and function.
• The findings provide detailed structural information at the residue level for this important membrane protein fragment.