Hidden Multivalency in Phosphatase Recruitment by a Disordered AKAP Scaffold

Area of Science:

• Molecular Biology
• Cellular Signaling
• Protein-Protein Interactions

Background:

• Disordered scaffold proteins, such as AKAP5, utilize Short Linear Motifs (SLiMs) to assemble cellular signaling complexes.
• AKAP5 anchors protein kinase A (PKA) and Calcineurin, and recruits the TRPV1 receptor.

Purpose of the Study:

• To investigate the binding interactions between Calcineurin and AKAP5 beyond the known PxIxIT motif.
• To understand how multiple SLiMs with varying affinities contribute to signalosome regulation.

Main Methods:

• Biochemical assays
• Biophysical approaches

Main Results:

• The Calcineurin binding groove recognizes additional, lower-affinity SLiMs on AKAP5, not previously identified.
• AKAP5 utilizes a spectrum of SLiMs, ranging in affinity, to assemble signaling complexes.
• These interactions involve hydrophobic forces and are analogous to, yet distinct from, DNA-protein binding.

Conclusions:

• AKAP5's C-terminus is rich in low-affinity SLiMs that, with the canonical PxIxIT motif, form a regulated signalosome.
• This multi-affinity binding mechanism allows for both stable enzyme anchoring and dynamic signaling responses.
• The findings elucidate a complex regulatory system mediated by intrinsically disordered proteins and their SLiMs.