The mitochondrial processing peptidase: function and specificity

Area of Science:

• Mitochondrial biology
• Enzymology
• Protein processing

Background:

• Mitochondrial precursor proteins require targeting signals for import.
• Mitochondrial processing peptidase (MPP) removes these signals in the mitochondrial matrix.
• MPP is a heterodimeric metalloendopeptidase crucial for mitochondrial function.

Purpose of the Study:

• To elucidate the distinct roles of MPP's alpha and beta subunits in processing mitochondrial presequences.
• To investigate the interaction between MPP and mitochondrial targeting/cleavage signals.
• To understand the structural requirements for MPP-mediated presequence cleavage.

Main Methods:

• Enzymatic assays using chemically synthesized peptides corresponding to mitochondrial presequences.
• Analysis of MPP's conserved zinc-binding motif (HXXEHX76E) in the beta-subunit.
• Investigation of presequence structure (e.g., helix-turn-helix) in membrane-mimetic environments.

Main Results:

• Both alpha and beta subunits are essential for MPP's catalytic activity.
• The alpha-subunit likely recognizes a three-dimensional motif of the presequence, while the beta-subunit contains the active site.
• Cleavage signals are distinct from targeting signals, though they may overlap.
• A helix-turn-helix motif is necessary but not sufficient for cleavage.
• Alpha-MPP binding tolerates presequence mutations, potentially presenting degenerate cleavage sites to beta-MPP.

Conclusions:

• MPP functions as an endoprotease with specialized roles for its alpha and beta subunits.
• The precise conformation of presequences bound to MPP remains largely uncharacterized.
• Understanding MPP function is key to comprehending mitochondrial protein import and regulation.