Conformational changes in G-CSF/Receptor complex as investigated by isotope-edited FTIR spectroscopy

Area of Science:

• Structural Biology
• Biophysics
• Molecular Interactions

Background:

• Granulocyte-colony stimulating factor (G-CSF) is crucial for neutrophil production.
• Cytokine receptor binding typically induces conformational changes in the receptor for signal transduction.
• The structural dynamics of G-CSF and its receptor upon complex formation are not fully understood.

Purpose of the Study:

• To investigate the conformational changes of G-CSF and its receptor upon complex formation.
• To determine the impact of complex formation on the stability of G-CSF and receptor structures.
• To elucidate the role of G-CSF's unique 310 helix in receptor binding.

Main Methods:

• Isotope-edited Fourier-transform infrared (FTIR) spectroscopy was employed.
• Uniformly 13C/15N isotope-labeled G-CSF was prepared for spectral resolution.
• Comparative analysis of FTIR spectra of G-CSF, its receptor, and their complex was performed.

Main Results:

• G-CSF's AB loop, containing a 310 helix, likely transforms into an alpha-helix upon receptor binding.
• The receptor exhibits a minor increase in alpha-helical conformation.
• Complex formation significantly stabilizes protein structures, increasing G-CSF's alpha-helix melting transition by ~30°C and the receptor's beta-strand by ~15°C.

Conclusions:

• Ligand-receptor complex formation induces conformational changes in both G-CSF and its receptor.
• G-CSF binding stabilizes approximately 15% of receptor residues and the entire alpha-helical content of G-CSF.
• These findings suggest a potential physiological role for the 310 helix in G-CSF's receptor binding activity.