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Subunit IV of cytochrome bc1 complex from Rhodobacter sphaeroides. Localization of regions essential for interaction
S C Tso1, S K Shenoy, B N Quinn
1Department of Biochemistry & Molecular Biology, Oklahoma State University, Stillwater, Oklahoma 74078, USA.
The Journal of Biological Chemistry
|April 5, 2000
Summary
Researchers identified key regions in subunit IV (residues 86-109 and 1-85) essential for restoring bc(1) activity in Rhodobacter sphaeroides. These regions are crucial for complex assembly and interaction with cytochrome b.
Area of Science:
- Biochemistry
- Molecular Biology
- Microbiology
Background:
- The bc(1) complex is vital for cellular respiration and energy production in many organisms.
- Understanding subunit interactions within the bc(1) complex is crucial for elucidating its function.
- Rhodobacter sphaeroides provides a model system for studying bacterial bc(1) complex assembly and activity.
Purpose of the Study:
- To identify specific regions of subunit IV essential for the reconstitution of bc(1) activity in Rhodobacter sphaeroides.
- To determine the role of subunit IV's C-terminal region in its assembly into the bc(1) complex.
- To map the interaction sites between subunit IV and cytochrome b within the core complex.
Main Methods:
- Generation and characterization of recombinant subunit IV mutants with C-terminal truncations.
- Assay of the reconstitutive activity of mutant subunit IVs with the three-subunit core complex.
- Analysis of subunit IV association with the core complex using membrane preparations.
- Identification of interacting regions through further mutant analysis and proximity to cytochrome b.
Main Results:
- Residues 86-109 of subunit IV are essential for its association with the core complex and overall reconstitutive activity.
- Mutants lacking the transmembrane helix region (86-109) failed to associate with the core complex.
- Regions 41-53 and 77-85 of subunit IV are required for bc(1) activity restoration after incorporation, interacting with cytochrome b on the cytoplasmic side.
Conclusions:
- The transmembrane helix of subunit IV (residues 86-109) is critical for its assembly into the bc(1) complex.
- Specific regions within the N-terminal portion of subunit IV (41-53 and 77-85) mediate interaction with cytochrome b, restoring enzymatic activity.
- These findings provide detailed insights into the structural requirements for bc(1) complex assembly and function in Rhodobacter sphaeroides.