Structural responses to cavity-creating mutations in an integral membrane protein

Area of Science:

• Biochemistry
• Structural Biology
• X-ray Crystallography

Background:

• The purple bacterial reaction center is crucial for photosynthesis.
• Cofactors like ubiquinone and bacteriopheophytin are essential for its function.
• Understanding cofactor absence effects on protein structure is key.

Purpose of the Study:

• To investigate structural changes in reaction center mutants lacking specific cofactors.
• To determine the impact of bacteriopheophytin and ubiquinone absence on protein structure.
• To correlate structural findings with thermal stability and protein dynamics.

Main Methods:

• X-ray crystallography was employed to determine the structures of mutant reaction centers.
• Mutants were engineered to lack bacteriopheophytin (AM149W) or ubiquinone (AM248W).
• Crystallographic data were collected and refined to high resolution (2.2 Å and 2.8 Å).

Main Results:

• The AM149W mutant (lacking bacteriopheophytin) showed minimal protein structural changes.
• The AM248W mutant (lacking ubiquinone) also exhibited only minor structural alterations.
• Both mutants displayed reduced thermal stability in the native membrane.
• Observed structural stability is attributed to protein rigidity and membrane environment.

Conclusions:

• The purple bacterial reaction center maintains structural integrity despite the absence of major cofactors.
• Protein rigidity and the surrounding membrane environment play significant roles in stabilizing the structure.
• Small molecules and ions may fill internal cavities created by cofactor removal.