Question

How do hydrophobic and hydrophilic amino acid residues affect how a protein is folded? Include in your response these two examples of proteins: membrane protein and cytosolic protein.

Answer 1

Protein folding is based on the interactions with other amino acids present with in the protein molecule itself (direct interactions) and also interactions with the solvent particles ( solvent based ) present around . When a protein molecule is formed it is a long chain of amino acids. Some amino acids have +ve charge, some -ve charge, some hydrophilic and some hydrophobic amino acids.

Hydrophobic effect is the major driving force for the folding of globular proteins. Hydrophobic side chains enter in to the core of the protein away from the hydrophilic medium. More hydrophobic side chains are folded if there is more water around, give stability to the protein molecule in the aqueous water medium. All hydrophilic amino acids are exposed to surroundings which make hydrogen bonds with the water molecules in the medium giving a rigid structure to the protein.

Cytosolic proteins are folded in a way where the hydrophobic amino acids are kept away from the surrounding water and hydrophilic amino acids are on the periphery forming hydrogen bonds with water surrounding. Where as the membrane proteins are folded in the other way. Which means, hydrophobic amino acids are in the periphery as the membrane is mainly made of lipids which are hydrophobic too. The interior of the proteins of the membrane are with hydrophilic amino acids which will allow the water soluble substances and other polar molecules to pass through or to be away from the surrounding hydrophobic membrane lipids.

So the way two types of proteins fold is different because of the surroundings they are in.