The diagram below shows part of a transmembrane protein. The yellow coloured L subunit has a disordered loop within the hydrophobic core of the lipid membrane. Does this then invalidate the general rule that transmembrane proteins span the lipid bilayer as alpha helices or beta sheets? Explain.
What will be an ideal response?
Answer: It does not invalidate the general rule because the helix is still apparent and the loop does not completely 'span' the membrane. The loop can exist in a lipid environment if it contains hydrophobic or non-polar residues. However it does show that there may be other potential ways for the protein to fold within a membrane that we don't yet appreciate because the structure of so few transmembrane proteins are known.
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What will be an ideal response?