Human interleukin 4. The solution structure of a four-helix bundle protein

Area of Science:

• Biochemistry
• Structural Biology
• Molecular Biophysics

Background:

• Human interleukin 4 (IL-4) is a critical cytokine involved in immune responses.
• Understanding the three-dimensional (3D) structure of IL-4 is essential for elucidating its biological functions and interactions.
• Previous structural information may be limited or based on predictions.

Purpose of the Study:

• To determine the high-resolution solution structure of human interleukin 4.
• To characterize the topological arrangement and residue distribution within the IL-4 protein.

Main Methods:

• Utilized heteronuclear 13C and 15N three-dimensional nuclear magnetic resonance (n.m.r.) spectroscopy.
• Employed a dynamical simulated annealing protocol for structure calculation.
• Integrated 1735 distance restraints, 101 phi angle restraints, and 27 hydrogen bond restraints.

Main Results:

• The solution structure of human IL-4 was determined as a four-helix bundle protein.
• A left-handed up-up-down-down topology was identified for the four helices.
• Hydrophobic residues, especially leucines, cluster in the core, while charged residues are on the surface.

Conclusions:

• The determined solution structure provides detailed insights into the folding and organization of human IL-4.
• The structural features, including the helix topology and residue distribution, are likely key to IL-4's biological activity.
• Comparison with predicted and crystal structures aids in understanding variations and conserved features among helix bundle proteins.