Differences in dynamic structure of LC8 monomer, dimer, and dimer-peptide complexes.

Area of Science:

• Biochemistry
• Structural Biology
• Molecular Dynamics

Background:

• Dynein light chain LC8 dimerization forms binding grooves.
• Dimerization is sensitive to pH, protein concentration, and phosphorylation.
• A phosphomimetic mutation can induce LC8 monomerization and dissociation.

Purpose of the Study:

• Characterize the dynamic structure and unfolding of monomeric LC8 (H55K mutant).
• Investigate how ligand binding affects LC8 backbone dynamics.
• Elucidate the role of conformational flexibility in LC8 function.

Main Methods:

• Backbone (15)N relaxation experiments to study protein dynamics.
• Analysis of LC8 mutant H55K dynamics at neutral pH.
• Studying LC8 dynamics upon binding to Swallow (Swa) and dynein intermediate chain (IC) peptides.

Main Results:

• LC8 monomer exhibits heterogeneous dynamics compared to the dimer, particularly in binding groove residues.
• Conformational heterogeneity is retained in LC8/IC but lost in LC8/Swa complexes.
• Binding to Swa peptide shows reduced motional complexity and less favorable binding entropy than IC.

Conclusions:

• Monomeric LC8 samples pre-binding conformations, favored in the dimer.
• Ligand binding induces specific conformational changes in LC8.
• The flexibility of the beta 3 strand is crucial for LC8 dimerization and ligand binding specificity.