MMP activation-associated aminopeptidase N reveals a bivalent 14-3-3 binding motif

Area of Science:

• Biochemistry
• Molecular Biology
• Cell Signaling

Background:

• Aminopeptidase N (APN, CD13) is a cell surface enzyme crucial for cellular functions, including signal transduction.
• APN mediates the activation of matrix metalloproteinases (MMPs), enzymes implicated in tissue remodeling and various diseases like cancer and fibrosis.
• The precise mechanism of APN-driven MMP activation, particularly the role of 14-3-3 adapter proteins, remains incompletely understood.

Purpose of the Study:

• To identify and characterize 14-3-3 protein binding sites on Aminopeptidase N (APN).
• To elucidate the structural basis of APN-14-3-3 interactions and their impact on APN-mediated signaling.
• To provide foundational insights into the initial steps of APN-driven matrix metalloproteinase (MMP) activation.

Main Methods:

• Synthesis and characterization of phosphorylated peptides derived from APN.
• Fluorescence polarization assays and thermodynamic analysis to study APN-14-3-3 binding.
• X-ray crystallography to determine the atomic structures of 14-3-3σ bound to APN-derived peptides.

Main Results:

• Identification of a canonical 14-3-3 binding site (site 1) in the N-terminal region of APN.
• Discovery of a secondary, noncanonical binding site (site 2) that dramatically enhances binding affinity when paired with site 1.
• Structural elucidation of mono- and bivalent 14-3-3 interactions with APN peptides at atomic resolution.

Conclusions:

• The identified 14-3-3 binding sites are critical for the initial steps of APN-mediated MMP activation.
• The synergistic binding of 14-3-3 proteins to APN, involving both canonical and noncanonical sites, is a key regulatory mechanism.
• These findings offer a molecular basis for understanding APN signaling and present potential targets for therapeutic intervention in APN-related diseases.