14-3-3zeta binds a phosphorylated Raf peptide and an unphosphorylated peptide via its conserved amphipathic groove

Area of Science:

• Biochemistry
• Structural Biology
• Molecular Signaling

Background:

• 14-3-3 proteins are crucial regulators of signal transduction, cell cycle, and apoptosis.
• They bind various ligands, including phosphorylated motifs (e.g., Raf-1, Bad) and unphosphorylated motifs (e.g., glycoprotein Ib, exoenzyme S).

Purpose of the Study:

• To elucidate the structural basis of 14-3-3 zeta isoform's interaction with both phosphorylated and unphosphorylated ligands.
• To understand the mechanism by which 14-3-3 proteins bind diverse target molecules.

Main Methods:

• X-ray crystallography was used to determine the structures of 14-3-3 zeta in complex with two distinct peptide ligands.
• Peptide ligands included a Raf-derived phosphopeptide and an unphosphorylated peptide identified through phage display.

Main Results:

• Crystal structures revealed that both phosphopeptide and unphosphorylated peptide bind to overlapping but distinct sites within a conserved amphipathic groove on 14-3-3.
• The phosphoserine of the pS-Raf-259 peptide interacted with basic residues, while the unphosphorylated R18 peptide utilized its amphipathic sequence and acidic groups to bind the same basic cluster.
• 14-3-3 proteins are dimeric, with two peptide-binding grooves oriented antiparallel.

Conclusions:

• The dual binding capability of 14-3-3's grooves allows for the accommodation of different ligand motifs.
• This structural plasticity explains how 14-3-3 proteins can mediate signal transduction by inducing homodimer or heterodimer formation in target proteins.