Structure of an enzyme-derived phosphoprotein recognition domain

Area of Science:

• Molecular Biology
• Structural Biology
• Cell Biology

Background:

• Membrane Associated Guanylate Kinases (MAGUKs) possess a guanylate kinase-like domain (GK(dom)).
• This domain is structurally derived from the enzyme Guanylate Kinase (GK(enz)).

Purpose of the Study:

• To elucidate the structural basis for the GK(dom) in MAGUKs recognizing phosphoproteins.
• To understand the functional transition of GK(enz) to a protein-binding module.

Main Methods:

• X-ray crystallography to determine the structure of the Discs large (Dlg)-Partner of Inscuteable (Pins) complex.
• Site-directed mutagenesis to analyze protein-protein interactions.

Main Results:

• The Dlg GK(dom) recognizes the phosphorylated form of Pins.
• The guanine nucleotide-binding pocket (GBD) within GK(dom) is repurposed for protein interaction.
• Mutational analysis confirmed the GBD binds Pins and another MAGUK ligand, MAP1a.
• The GK(dom) in the Dlg-Pins complex adopts an 'open' conformation, unlike the 'closed' conformation of active GK(enz).

Conclusions:

• The guanylate kinase domain is a versatile platform for both nucleotide and protein binding.
• This structural plasticity allows MAGUKs to mediate protein-protein interactions crucial for complex assembly.
• The loss of the conformational change upon GMP binding highlights the functional divergence of GK(dom) from GK(enz).