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Proline substitutions are not easily accommodated in a membrane protein
Sarah Yohannan1, Duan Yang, Salem Faham
1Department of Chemistry and Biochemistry, DOE Center for Genomics and Proteomics, Molecular Biology Institute, 655 Boyer Hall, 611 Charles E. Young Dr. E, University of California, Los Angeles, Los Angeles, CA 90095-1570, USA.
Journal of Molecular Biology
|August 18, 2004
Summary
Proline substitutions in bacteriorhodopsin
Area of Science:
- Membrane protein structure and function
- Protein biochemistry
- Biophysics
Background:
- Proline residues are common in transmembrane helices.
- Proline substitutions can cause structural deviations in helices.
- The tolerance of proline substitutions in membrane proteins is not fully understood.
Purpose of the Study:
- To investigate the impact of proline substitutions on bacteriorhodopsin helix B.
- To determine how proline side-chains are structurally accommodated at different positions within transmembrane helices.
Main Methods:
- Site-directed mutagenesis to introduce proline substitutions in bacteriorhodopsin helix B.
- Functional assays to assess protein activity.
- Structural analysis of mutant proteins using X-ray crystallography.
Main Results:
- Six out of 15 proline substitutions resulted in inactive protein.
- All other substitutions were destabilizing to varying degrees.
- Proline substitutions near the N-terminus were less destabilizing than those in the middle of the helix.
- K41P mutation caused local structural changes, while A51P caused widespread structural alterations.
Conclusions:
- Proline is not easily accommodated in transmembrane helices.
- The tolerance to proline substitution depends on its position within the helix.
- Structural accommodation of proline varies based on its location, leading to local or distributed changes.