A protein-specific priority code in presequences determines the efficiency of mitochondrial protein import

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Mitochondrial biogenesis requires importing hundreds of cytosolic precursor proteins.
• These proteins often possess N-terminal presequences that act as mitochondrial targeting signals.
• Presequences typically form amphipathic helices but vary in structure and length.

Purpose of the Study:

• To classify mitochondrial presequences based on their features.
• To investigate the role of presequence groups in protein import efficiency.
• To identify novel factors involved in mitochondrial precursor targeting.

Main Methods:

• Classification of presequences into seven distinct groups.
• Development and application of the IQ-Compete (Import and de-Quenching Competition assay) for in vivo import monitoring.
• Mass spectrometry to identify protein interactions with presequences.

Main Results:

• Presequences were categorized into seven groups, with Group A showing enhanced in vitro import characteristics.
• The IQ-Compete assay confirmed improved import competence for Group A presequences in vivo.
• Mass spectrometry revealed that the Oxa1 presequence (Group A) recruits TOMM34, a tetratricopeptide repeat (TPR)-containing protein.

Conclusions:

• TOMM34 and Cns1 function as presequence-specific targeting factors, boosting the import of certain mitochondrial precursors.
• Mitochondrial presequences contain a protein-specific code dictating their targeting mechanisms.
• This study reveals a novel layer of specificity in mitochondrial protein import.