Rhodobacter capsulatus forms a compact crescent-shaped LH1-RC photocomplex

Area of Science:

• Bacteriology
• Structural Biology
• Biochemistry

Background:

• Rhodobacter capsulatus is a model organism for bacterial photosynthesis research.
• The light-harvesting 1-reaction center (LH1-RC) complex is key to this process.
• Rba. capsulatus lacks protein-U, present in Rba. sphaeroides LH1-RC.

Purpose of the Study:

• To determine the cryo-electron microscopy (cryo-EM) structure of the Rba. capsulatus LH1-RC.
• To understand the role of PufX in LH1-RC complex assembly and function.
• To investigate the structural basis for monomeric LH1-RC formation.

Main Methods:

• Purification of the Rba. capsulatus LH1-RC complex using DEAE chromatography.
• Cryo-electron microscopy (cryo-EM) for structural determination.
• Analysis of PufX conformation and interactions within the complex.

Main Results:

• The Rba. capsulatus LH1-RC forms a compact, crescent-shaped structure with 10 LH1 αβ-subunits.
• Four αβ-subunits, homologous to those near protein-U in Rba. sphaeroides, were absent.
• PufX adopts a unique conformation, self-associating and interacting with adjacent polypeptides, preventing dimerization.

Conclusions:

• The structure reveals minimal requirements for LH1-RC monomer formation.
• PufX's conformation dictates LH1-RC assembly and prevents dimer formation.
• Structural findings provide insights into LH1-RC spectroscopic properties and energy transfer.