Question

Explain how the three-dimensional structure of a cytosolic protein differs from a transmembrane protein in terms of the amino acid distribution and folding.

Answer 1

Cytosolic proteins are found in the cytosol. They are not attached to the membrane. These are mainly made of hydrophilic residues. There are no disulfide bonds present in these proteins because there is a reducing environment inside the cytosol whereas transmembrane proteins are amphipathic, having regions that are hydrophobic and regions that are hydrophilic. Their hydrophobic regions pass through the membrane and interact with the hydrophobic tails of the lipid molecules in the interior of the bilayer, where they are sequestered away from water. Their hydrophilic regions are exposed to water on either side of the membrane. The hydrophobicity of some of these transmembrane proteins is increased by the covalent attachment of a fatty acid chain that inserts into the cytosolic monolayer of the lipid bilayer. Numerous disulfide bonds assist in their folding.