Related protein-protein interaction modules present drastically different surface topographies despite a conserved...

Area of Science:

• Molecular Biology
• Cell Biology
• Structural Biology

Background:

• Subcellular localization of cAMP-dependent protein kinase (PKA) is mediated by A-Kinase Anchoring Proteins (AKAPs).
• AKAPs interact with the regulatory subunit dimers (RIalpha and RIIalpha) of PKA.
• The N-terminal dimerization and docking (D/D) domain of regulatory subunits is crucial for AKAP interaction and localization.

Purpose of the Study:

• To determine the solution structure of the RIalpha D/D module.
• To compare the structural and functional differences in AKAP binding between RIalpha D/D and RIIalpha D/D.

Main Methods:

• Nuclear Magnetic Resonance (NMR) spectroscopy to solve the solution structure of RIalpha D/D.
• Structural comparison with previously determined RIIalpha D/D structure.

Main Results:

• The RIalpha D/D module is a compact structure featuring unusual interchain disulfide bonds.
• RIalpha D/D possesses a deep cleft for AKAP binding, contrasting with the shallow hydrophobic groove found in RIIalpha D/D.
• Despite a conserved X-type four-helix bundle, RIalpha D/D and RIIalpha D/D exhibit distinct dimeric topographies.

Conclusions:

• The structural differences in the D/D domains of RIalpha and RIIalpha subunits dictate distinct AKAP binding mechanisms.
• Understanding these structural variations provides insight into the precise subcellular targeting of PKA isoforms.