INA complex liaises the F₁F_o-ATP synthase membrane motor modules

Area of Science:

• Mitochondrial biogenesis and function
• Protein complex assembly and regulation
• Membrane protein structure and dynamics

Background:

• F1F0-ATP synthase couples proton flux to ATP synthesis, requiring precise assembly of its membrane-embedded motor.
• Formation of the proton channel, involving Atp9 and Atp6, is a critical, regulated step to maintain the proton gradient.
• Mitochondrial protein import and maturation pathways are essential for functional enzyme assembly.

Purpose of the Study:

• To elucidate the role of the INA complex (INAC) in the assembly of the F1F0-ATP synthase.
• To investigate how INAC facilitates the formation of the proton-conducting channel within the ATP synthase motor.
• To understand the mechanism by which INAC regulates the association of key subunits during assembly.

Main Methods:

• Analysis of mitochondrial protein complexes using co-immunoprecipitation and mass spectrometry.
• Studying the effects of INAC depletion or mutation on ATP synthase assembly intermediates.
• Investigating the binding interactions between INAC, Atp6, Atp8, and the Atp9 ring.

Main Results:

• The INA complex (INAC) directly promotes the association of the Atp9 ring with Atp6, a key step in motor module formation.
• INAC binds to newly synthesized mitochondrial-encoded Atp6 and Atp8, remaining associated until the F1 portion is assembled.
• Loss of INAC leads to the accumulation of unassembled F1 portions and disrupts proton channel formation.

Conclusions:

• The INA complex (INAC) acts as a critical assembly factor, ensuring the correct formation of the F1F0-ATP synthase proton channel.
• INAC maintains assembly intermediates in a state conducive to the terminal assembly step, facilitating motor module formation.
• This study reveals a novel regulatory mechanism essential for efficient mitochondrial ATP synthesis.