The amino acid sequences below represent the sequences of transmembrane helices. The characteristics of ? helices that form a channel are different from those that form a single transmembrane domain
Select the helix that forms a single transmembrane domain.
(a) VGHSLSIFTLVISLGIFVFF
(b) IMIVLVMLLNIGLAILFVHF
(c) ILHFFHQYMMACNYFWMLCE
(d) VTLHKNMFLTYILNSMIIII
Choice (b) is correct. The peptide sequences for options (a), (c), and (d) are amphipathic—that is, they contain a hydrophilic amino acid every 3–4 amino acids in the sequence. This indicates they may be part of a protein that makes a channel in the membrane, and they require hydrophobic amino acids on the surface that interacts with the lipid bilayer and a hydrophilic surface on the inside of the channel. Option (b) is the only sequence that is completely hydrophobic, indicating that it forms a helix in which all the side chains interact with the lipid bilayer.
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