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Conformations of proline residues in membrane environments
C M Deber1, M Glibowicka, G A Woolley
1Research Institute, Hospital for Sick Children, Toronto, Ontario, Canada.
Biopolymers
|January 1, 1990
Summary
Proline residues in transmembrane helices can adopt specific conformations, influencing protein function. This study synthesized a peptide to investigate proline
Area of Science:
- Structural Biology
- Membrane Protein Biochemistry
- Biophysical Chemistry
Background:
- Proline residues, despite being hydrophilic and helix-breaking, are found in alpha-helical transmembrane segments of integral membrane proteins.
- The X-Pro peptide bond's cis/trans isomerism and tertiary amide character enable participation in specific hydrogen-bonded structures and ligand interactions.
- A consensus sequence triad, Leu-Pro-Phe, was identified in intramembranous proline residues of transport proteins.
Purpose of the Study:
- To investigate the conformational behavior of proline-containing sequences within membrane environments.
- To explore the role of the Leu-Pro-Phe triad in the structure and function of transmembrane segments.
- To synthesize and analyze hydrophobic peptides mimicking intramembranous protein segments.
Main Methods:
- Synthesis of a hydrophobic hexapeptide, t-butyloxycarbonyl-L-Ala-L-Ala-L-Ala-L-Leu-L-Pro-L-Phe-OH (t-Boc-AAALPF-OH), with potential membrane affinity.
- Partitioning of the synthesized peptide into model membrane environments (lipid micelles).
- Conformational analysis using 75-MHz 13C-NMR and 300-MHz 1H-NMR spectroscopy to monitor peptide structure.
Main Results:
- NMR data revealed specific conformations for the membrane-bound hexapeptide.
- The Leu-Pro-Phe triad was observed to adopt an intramolecularly H-bonded inverse gamma-turn conformation in the membrane environment.
- Carbonyl carbons of Leu and Pro, along with peptide alpha, beta, and aromatic protons, provided spectral evidence for this conformation.
Conclusions:
- Proline residues in transmembrane helices can adopt specific, intramolecularly H-bonded conformations, such as inverse gamma-turns.
- The structural flexibility of proline-containing segments contributes to the functional roles of membrane-buried prolines in transport proteins.
- This study provides insights into the structural basis of proline's role in membrane protein function and stability.