DPP8/9 processing of human AK2 unmasks an IAP binding motif

Area of Science:

• Mitochondrial biology
• Protein regulation
• Ubiquitination pathways

Background:

• Adenylate kinase 2 (AK2) is crucial for mitochondrial adenine nucleotide exchange.
• AK2 import into mitochondria depends on the MIA40 system.
• Cytosolic AK2 stability is regulated by N-terminal processing via dipeptidyl peptidases DPP8 and DPP9, leading to proteasomal degradation.

Purpose of the Study:

• To investigate the mechanism of cytosolic AK2 degradation.
• To identify the E3 ligases involved in AK2 regulation.
• To explore the role of N-terminal processing in AK2 stability and substrate recognition.

Main Methods:

• Identification of IAP-binding motifs (IBMs) in AK2.
• Analysis of AK2 interaction with Inhibitors of Apoptosis (IAPs).
• Assessment of N-terminal acetylation by NatA on AK2 stability.
• Genome-wide in silico screening for DPP8/9 substrates with unmaskable IBMs.
• Experimental validation using EIF2A as a model substrate.

Main Results:

• Cytosolic AK2 degradation is mediated by IAPs, involving an IBM exposed by DPP8/9 processing.
• N-terminal acetylation by NatA prevents AK2-IAP interaction, stabilizing AK2.
• A genome-wide screen identified 129 potential substrates with DPP8/9-unmaskable IBMs.
• DPP8/9-mediated IBM unmasking and subsequent IAP targeting was confirmed for EIF2A.

Conclusions:

• DPP8/9-mediated N-terminal processing exposes IAP-binding motifs, marking proteins like AK2 for degradation.
• N-terminal acetylation by NatA acts as a protective mechanism against IAP-mediated degradation.
• DPP8/9-mediated unmasking of IBMs represents a general regulatory mechanism for protein stability.