A proposed common structure of substrates bound to mitochondrial processing peptidase

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• Mitochondrial processing peptidase (MPP) is a crucial metalloendopeptidase.
• MPP removes N-terminal presequences from mitochondrial protein precursors.
• Understanding substrate interaction with MPP is vital for mitochondrial protein import.

Purpose of the Study:

• To elucidate the structural basis of substrate binding to MPP.
• To investigate the role of intervening sequence length in substrate-MPP interaction.
• To map the binding sites of presequence elements within MPP.

Main Methods:

• Synthesis of fluorescently labeled peptide substrates with varying lengths.
• Utilizing fluorescence resonance energy transfer (FRET) to measure distances between probes.
• Employing intermolecular FRET with modified MPP beta-subunit and peptide substrates.

Main Results:

• FRET measurements revealed consistent distances between N-terminal and +4 position probes, irrespective of intervening sequence length.
• Intermolecular FRET confirmed that donor-acceptor distances remained constant across different peptide lengths.
• Specific interactions occur between MPP and both the N-terminal and cleavage site regions of the substrate.

Conclusions:

• The N-terminal portion and cleavage site of the presequence bind to specific sites on MPP.
• The intervening sequence between these binding regions is flexible when the substrate is bound.
• MPP exhibits structural adaptability in accommodating presequences of varying lengths.