Which force is primarily responsible for embedding transmembrane α-helices into the bilayer?
Thermodynamic and kinetic aspects of alpha-helical insertion illuminate hydrophobic driving forces. Nascent chain emerges from ribosome tunnel, signal recognition particle SRP binds hydrophobic signal anchor, delivers ribosome-nascent complex to SRP receptor at endoplasmic reticulum membrane, GTP hydrolysis releases chain to Sec61 translocon aqueous channel laterally gated by plug displacement. Partitioning of hydrophobic segment into lipid phase determined by apparent free energy Delta G apparent measured via reporter Lep assays where insertion efficiency correlates with hydrophobicity scale:
Ref: White and von Heijne, Transmembrane Helices and Hydrophobicity Scale, Annu Rev Biophys.