An ATP13A1-assisted topogenesis pathway for folding multi-spanning membrane proteins

Area of Science:

• Molecular Biology
• Cell Biology
• Protein Folding

Background:

• Multi-spanning membrane proteins often have poorly hydrophobic transmembrane domains (pTMDs).
• Nascent pTMDs pose challenges for the translocon during insertion into the endoplasmic reticulum.
• The mechanism for discerning and integrating these difficult pTMDs into mature protein structures is not fully understood.

Purpose of the Study:

• To elucidate the post-translational pathway governing the recognition and integration of pTMDs.
• To understand how difficult pTMDs are correctly folded and embedded within multi-spanning membrane proteins.

Main Methods:

• Utilized the six-spanning protein ABCG2 (adenosine triphosphate-binding cassette transporter G2) as a model system.
• Employed cultured human cells to investigate protein topogenesis.
• Investigated the role of P5A-ATPase ATP13A1 in the process.
• Examined the effects of ATP13A1 depletion and disruption of pTMD residues.

Main Results:

• Demonstrated that ABCG2's pTMD2 can pass through the translocon into the ER lumen, forming an intermediate with mis-oriented transmembrane domains (TMDs).
• Showed that P5A-ATPase ATP13A1 is recruited post-translationally to facilitate TMD re-orientation and proper folding.
• Observed that ATP13A1 depletion or disruption of pTMD residues leads to arrested intermediates with exposed and mis-oriented TMDs.

Conclusions:

• A novel post-translational topogenesis pathway is responsible for the integration of difficult pTMDs.
• ATP13A1 plays a crucial role in the late-stage folding and correct burial of pTMDs, preventing lipid exposure.
• This mechanism ensures the proper structure and function of multi-spanning membrane proteins containing challenging hydrophobic regions.