Role of Aromatic Side Chains in the Folding and Thermodynamic Stability of Integral Membrane Proteins
- 12 June 2007
- journal article
- Published by American Chemical Society (ACS) in Journal of the American Chemical Society
- Vol. 129 (26), 8320-8327
- https://doi.org/10.1021/ja068849o
Abstract
Aromatic residues are frequently found in helical and β-barrel integral membrane proteins enriched at the membrane−water interface. Although the importance of these residues in membrane protein folding has been rationalized by thermodynamic partition measurements using peptide model systems, their contribution to the stability of bona fide membrane proteins has never been demonstrated. Here, we have investigated the contribution of interfacial aromatic residues to the thermodynamic stability of the β-barrel outer membrane protein OmpA from Escherichia coli in lipid bilayers by performing extensive mutagenesis and equilibrium folding experiments. Isolated interfacial tryptophanes contribute −2.0 kcal/mol, isolated interfacial tyrosines contribute −2.6 kcal/mol, and isolated interfacial phenylalanines contribute −1.0 kcal/mol to the stability of this protein. These values agree well with the prediction from the Wimley−White interfacial hydrophobicity scale, except for tyrosine residues, which contribute more than has been expected from the peptide models. Double mutant cycle analysis reveals that interactions between aromatic side chains become significant when their centroids are separated by less than 6 Å but are nearly insignificant above 7 Å. Aromatic−aromatic side chain interactions are on the order of −1.0 to −1.4 kcal/mol and do not appear to depend on the type of aromatic residue. These results suggest that the clustering of aromatic side chains at membrane interfaces provides an additional heretofore not yet recognized driving force for the folding and stability of integral membrane proteins.This publication has 30 references indexed in Scilit:
- Ez, a Depth-dependent Potential for Assessing the Energies of Insertion of Amino Acid Side-chains into Membranes: Derivation and Applications to Determining the Orientation of Transmembrane and Interfacial HelicesJournal of Molecular Biology, 2007
- Positioning of proteins in membranes: A computational approachProtein Science, 2006
- Empirical lipid propensities of amino acid residues in multispan alpha helical membrane proteinsProteins: Structure, Function, and Bioinformatics, 2005
- A Study of the Membrane–Water Interface Region of Membrane ProteinsJournal of Molecular Biology, 2005
- High-resolution structure of the OmpA membrane domainJournal of Molecular Biology, 2000
- Genome‐wide analysis of integral membrane proteins from eubacterial, archaean, and eukaryotic organismsProtein Science, 1998
- Architecture of helix bundle membrane proteins: An analysis of cytochrome c oxidase from bovine mitochondriaProtein Science, 1997
- Non-random Distribution of Amino Acids in the Transmembrane Segments of Human Type I Single Span Membrane ProteinsJournal of Molecular Biology, 1993
- Strength and co-operativity of contributions of surface salt bridges to protein stabilityJournal of Molecular Biology, 1990
- Aromatic-Aromatic Interaction: A Mechanism of Protein Structure StabilizationScience, 1985