Residual flexibility in the topologically constrained multivalent complex between the GKAP scaffold and LC8 hub...

Area of Science:

• Molecular biology
• Structural biology
• Neuroscience

Background:

• Guanylate kinase-associated protein (GKAP) is a large postsynaptic scaffold protein.
• GKAP has two binding sites for the dynein light chain LC8.
• This arrangement suggests potential for varied complex formations.

Purpose of the Study:

• To investigate the complex formation between GKAP and LC8.
• To determine the stoichiometry and structural characteristics of the GKAP-LC8 complex.
• To explore the dynamics and flexibility within the assembled complex.

Main Methods:

• Nuclear magnetic resonance (NMR) spectroscopy to analyze protein interactions.
• Molecular dynamics calculations to simulate complex behavior.
• Biochemical assays to confirm complex stoichiometry.

Main Results:

• A well-defined hexameric complex of two GKAP molecules and two LC8 dimers was identified.
• The LC8-binding segment of GKAP is intrinsically disordered, retaining flexibility within the complex.
• Dynamic interactions and potential inter-dimer contacts were observed, alongside distinct flanking region interactions.

Conclusions:

• GKAP and LC8 form a stable hexameric complex with a fixed stoichiometry.
• Significant flexibility persists within the complex, particularly in the intrinsically disordered LC8-binding segments.
• This study demonstrates the coexistence of constrained stoichiometry and substantial flexibility in multivalent protein systems.