Filamentous chemokine CCL5 structure and the functional aspects

Area of Science:

• Biochemistry
• Structural Biology
• Cell Biology

Background:

• Human CC chemokine ligand 5 (hCCL5) exhibits self-assembly under physiological conditions, but the mechanisms and functions of its oligomerization are not fully understood.
• Previous studies suggested various intermolecular interactions mediate hCCL5 oligomerization, complicating structural determination.

Purpose of the Study:

• To elucidate the structural basis of hCCL5 oligomerization and filament formation.
• To investigate the functional significance of hCCL5 self-assembly, particularly the role of specific residues and the resulting filament structure.

Main Methods:

• Utilized a K25S mutation in hCCL5 to disrupt specific intermolecular interactions.
• Employed transmission electron microscopy (TEM) to visualize filament formation.
• Applied X-ray solution scattering and cryo-electron microscopy (cryo-EM) for structural determination of the large filaments.
• Confirmed filament packing using Nuclear Magnetic Resonance (NMR) spectroscopy.

Main Results:

• A K25S mutation induced the formation of helical hCCL5 filaments observed via TEM.
• Filamentous polymerization became dominant around 100 nM concentration, with higher-order assemblies forming at increased concentrations.
• Structural analysis revealed critical involvement of residues R44 and K45 in filament packing.
• The ⁴³TRKNR⁴⁷ sequence was identified as essential for both intracellular hCCL5 trafficking and extracellular glycosaminoglycan binding.

Conclusions:

• hCCL5 forms helical filaments, driven by specific intermolecular interactions involving residues R44 and K45.
• The identified sequence ⁴³TRKNR⁴⁷ plays a vital role in hCCL5's cellular trafficking and extracellular interactions.
• The study provides structural insights into hCCL5 oligomerization and its functional implications.