Question

11-18 A group of membrane proteins can be extracted from membranes only by using

detergents. All the proteins in this group have a similar amino acid sequence at their Cterminus:
-KKKKKXXC (where K stands for lysine, X stands for any amino acid, and C
stands for cysteine). This sequence is essential for their attachment to the membrane.
What is the most likely way in which the C-terminal sequence attaches these proteins to
the membrane?
(a) The cysteine residue is covalently attached to a membrane lipid.
(b) The peptide spans the membrane as an α helix.
(c) The peptide spans the membrane as part of a β sheet.
(d) The positively charged lysine residues interact with an acidic integral membrane
protein.

Answer 1

Proteins with the C-terminal sequence (-KKKKKXXC) are most likely attached to the membrane by the cysteine residue forming a covalent bond with a membrane lipid.

Step-by-step explanation:

The most likely way in which the C-terminal sequence attaches these proteins to the membrane is through the cysteine residue being covalently attached to a membrane lipid. This is because the sequence mentioned (-KKKKKXXC) contains a cysteine at the end, which is known to form thioester linkages with the fatty acid chains of lipids. This covalent linkage is a strong form of attachment within the hydrophobic interior of the membrane. Integral membrane proteins are anchored by hydrophobic interactions and, in some cases, have hydrophobic alpha-helical regions that interact with the hydrophobic interior of the membranes.