embedded protein
Summary
An embedded protein is an integral membrane protein, held in the phospholipid bilayer by nonpolar amino acids that contact the lipid tails. Many span the whole bilayer (transmembrane), but some sit only partly in it. It is removed from the membrane by detergent, not by mild salt washes.
Detail
Meaning: An embedded protein is another name for an integral membrane protein in the fluid mosaic model. The part of its surface that touches the fatty acid tails is rich in nonpolar R groups, while the parts exposed to water on either side carry polar and charged residues. Many cross the bilayer once or several times, often as α-helices of about 20 nonpolar residues, and some, such as porins, form β-barrels. Examples are channels, carriers, pumps like the Na⁺/K⁺ ATPase, receptors, and cell adhesion proteins. Because the bilayer is fluid, these proteins can usually diffuse laterally unless they are anchored.
On the MCAT: A passage may describe a protein that stays in the membrane after a high-salt wash but dissolves when detergent is added. That points to an integral protein. A sequence or hydropathy plot with a long run of nonpolar residues suggests a membrane-spanning segment. Questions also ask you to classify a channel as facilitated diffusion and a pump as active transport.
Common confusion: Embedded does not require crossing the full bilayer, because some integral proteins are inserted into only one leaflet. Peripheral proteins are different. They bind the membrane surface through noncovalent interactions with lipid heads or integral proteins, and mild changes in salt or pH can often release them.
Sources
- Lehninger Principles of Biochemistry
- Biochemistry (Berg, Tymoczko, Stryer)
- Molecular Biology of the Cell
Written for the MCAT and checked before it was published. For study reference only. Spotted an error? Let us know.