Operon structure and cotranslational subunit association direct protein assembly in bacteria

Area of Science:

• Molecular Biology
• Protein Biochemistry
• Bacterial Genetics

Background:

• Protein complex assembly is traditionally viewed as a post-translational process driven by random subunit collisions.
• Understanding the in vivo mechanisms governing efficient protein complex formation remains a key challenge in molecular biology.

Purpose of the Study:

• To investigate the spatiotemporal dynamics of bacterial luciferase (LuxA and LuxB) subunit assembly within the Escherichia coli cytosol.
• To determine whether protein assembly is coupled to the translation process and influenced by gene organization.

Main Methods:

• In vivo studies using Escherichia coli to analyze the assembly of bacterial luciferase subunits LuxA and LuxB.
• Investigating the impact of gene location and messenger RNA synthesis on subunit assembly efficiency.
• Examining the role of the ribosome-associated chaperone trigger factor in modulating cotranslational assembly.

Main Results:

• Bacterial luciferase subunits LuxA and LuxB assemble into complexes in close proximity to their synthesis sites.
• Assembly efficiency is significantly reduced when subunits are expressed from genes at distant chromosomal locations.
• Subunit assembly initiates cotranslationally on nascent LuxB, with trigger factor delaying interactions until the dimer interface is exposed.
• Protein assembly is directly coupled to translation, involving spatially confined, chaperoned cotranslational interactions.

Conclusions:

• Bacterial protein complex assembly is not a random post-translational event but is directly coupled to translation.
• Operon organization in bacteria facilitates spatial and temporal regulation, crucial for efficient cotranslational subunit assembly.
• This study reveals a fundamental mechanism linking gene expression, protein folding, and complex formation.