Distinctive Properties of Mla Proteins Differentiate Them From Classical ABC Transporter Components

Area of Science:

• Microbiology
• Structural Biology
• Biochemistry

Background:

• Gram-negative bacteria utilize the non-canonical ABC transporter, the maintenance of lipid asymmetry (Mla) system, to maintain outer membrane phospholipid asymmetry.
• The Mla system comprises three complexes: MlaA-OmpC/F in the outer membrane, MlaC in the periplasm, and the MlaFEDB complex in the inner membrane.
• Previous structural studies focused on the inner membrane complex and transport mechanisms, leaving individual component characteristics underexplored.

Purpose of the Study:

• To computationally analyze individual components of the Mla system (MlaA, MlaB, MlaE, MlaF) to characterize their unique features.
• To elucidate the conformational landscape and macromolecular arrangement of the Mla system using artificial intelligence.
• To propose a novel mechanism for non-vesicular phospholipid transport mediated by the Mla system.

Main Methods:

• Computational analysis of individual Mla components (MlaA, MlaB, MlaE, MlaF).
• Artificial intelligence for understanding the conformational landscape of MlaA.
• Analysis of protein-protein interactions and structural dynamics.

Main Results:

• Identification and characterization of unique features of MlaA, MlaB, MlaE, and MlaF.
• Detailed understanding of the MlaA C-terminal extension (CTE) dynamicity and protein orientation.
• Proposal of a novel 'bait-capture-pull' mechanism for ligand transport and insights into the MlaB-MlaF interface and MlaE's EQ loop.

Conclusions:

• The study provides a holistic understanding of the enigmatic Mla system's components and their functions.
• A novel 'bait-capture-pull' mechanism offers new insights into non-vesicular phospholipid transport.
• Findings shed light on previously poorly understood interfaces and structural elements within the Mla system.