Biochemistry Questions Biochemistry Questions / Describe the different types of protein-membrane interactions.

There are several types of protein-membrane interactions, allowing for peripheral and intrinsic membrane proteins.

Acyl chain anchors are attached to the N-terminal of the protein, attaching an acyl chain through acylation. This can be with palmitoyl acid, by the process of palmitoylation, allowing for insertion into the inner membrane leaflet of eukaryotes.

Prenylation involves the post-translational modification of the C-terminal of the amino acid sequence, attaching a prenyl group. The prenyl group is able to insert into the inner leaflet of eukaryotic cell membranes, allowing the attachment of proteins (such as enzymes) to the inner membrane. Prenylation requires the terminal residue to be a cysteine, with a-a-X residues being cleaved off to get to the cysteine (where a is an aliphatic amino acid).

GPI anchors are another form of protein-membrane interaction. This glycosyl phosphatidylinositol anchor is formed from the C-terminal modification of the protein, attaching an oligosaccharide bound to the phosphatidyl inositol, by an ethanolamine bond. This form of membrane-protein interaction is found on the exterior leaflet (exoplasmic face) of eukaryotic cells, allowing for the identification of cells, anchoring of enzymes, and other protein-membrane interactions.

Proteins can be inserted into the membrane, as with integral membrane proteins. These are able to form channels or other transport mechanisms, allowing for the uptake of ions, large molecules, and other species at a higher rate than would naturally be possible across the plasma membrane. Due to the strong interactions between these proteins and the membrane (due to the hydrophobic effect), it may be necessary to use strong detergents or organic solvents to remove these from the bilayer. On removal, many integral membrane proteins loose their rigidity, and may be hard to image (through X-ray crystallography, …). It is required that the residues interacting with the bilayer are hydrophobic, and the residues present in the channel are generally hydrophilic. This allows for transport through the membrane. The residues located at the edges of the bilayer may have larger, aromatic side chains - this provides additional protection against vertical movement, due to the additional interactions present.