title: Self-association of transmembrane alpha-helices in model membranes: importance of helix orientation and role of hydrophobic mismatch.
abstract: Interactions between transmembrane helices play a key role in almost all cellular processes involving membrane proteins. We have investigated helix-helix interactions in lipid bilayers with synthetic tryptophan-flanked peptides that mimic the membrane spanning parts of membrane proteins. The peptides were functionalized with pyrene to allow the self-association of the helices to be monitored by pyrene fluorescence and Trp-pyrene fluorescence resonance energy transfer (FRET). Specific labeling of peptides at either their N or C terminus has shown that helix-helix association occurs almost exclusively between antiparallel helices. Furthermore, computer modeling suggested that antiparallel association arises primarily from the electrostatic interactions between alpha-helix backbone atoms. We propose that such interactions may provide a force for the preferentially antiparallel association of helices in polytopic membrane proteins. Helix-helix association was also found to depend on the lipid environment. In bilayers of dioleoylphosphatidylcholine, in which the hydrophobic length of the peptides approximately matched the bilayer thickness, association between the helices was found to require peptide/lipid ratios exceeding 1/25. Self-association of the helices was promoted by either increasing or decreasing the bilayer thickness, and by adding cholesterol. These results indicate that helix-helix association in membrane proteins can be promoted by unfavorable protein-lipid interactions.
authors.affiliation: Department of Biochemistry of Membranes, Institute of Biomembranes and Bijvoet Center for Biomolecular Research, Utrecht University, Padualaan 8, NL-3584 CH Utrecht, The Netherlands. emma.sparr@fkem1.lu.se
authors.forename: Emma
authors.initials: E
authors.lastname: Sparr
authors.forename: Walter L
authors.initials: WL
authors.lastname: Ash
authors.forename: Petr V
authors.initials: PV
authors.lastname: Nazarov
authors.forename: Dirk T S
authors.initials: DT
authors.lastname: Rijkers
authors.forename: Marcus A
authors.initials: MA
authors.lastname: Hemminga
authors.forename: D Peter
authors.initials: DP
authors.lastname: Tieleman
authors.forename: J Antoinette
authors.initials: JA
authors.lastname: Killian
mesh_terms: D003198:Computer Simulation; D019281:Dimerization; D031541:Fluorescence Resonance Energy Transfer; D057927:Hydrophobic and Hydrophilic Interactions; D066298:In Vitro Techniques; D008051:Lipid Bilayers / Q000737:chemistry*; D008565:Membrane Proteins / Q000737:chemistry*; D008567:Membranes, Artificial; D008958:Models, Molecular; D046912:Multiprotein Complexes; D017433:Protein Structure, Secondary
chemical_list: D008051:Lipid Bilayers; D008565:Membrane Proteins; D008567:Membranes, Artificial; D046912:Multiprotein Complexes