What is an integral membrane protein? (with photos)

Integral membrane proteins weave their way through phospholipid bilayers.

An integral membrane protein, also known as an IMP, is one that spans the entire biological membrane of a cell. These proteins are permanently attached to the cell membrane and their function normally depends on being present in the membrane. Both structurally and functionally, they are integral parts of cell membranes.

Each integral membrane protein molecule has an intricate relationship to the membrane within which it is situated. Structurally, the IMP is usually placed so that the protein filaments are woven throughout the cell membrane structure. Protein sections protrude through the cell wall, inside or outside the cell, or in both directions. The protein molecule cannot function if it is not embedded in the membrane.

Numerous functional proteins are embedded in the cell membrane.

Another feature of the protein is that these proteins can be removed from the membrane only with a very specific chemical treatment. This is because the hydrophobic regions of the protein are protected within the phospholipid bilayer of the cell membrane. For this reason, detergents, denaturing solvents, and non-polar solvents must be used to disrupt the phospholipid bilayer and extract the integral protein from the membrane.

Within the class of integral membrane proteins there are several different categories of proteins, many of which are receptors and other types of cell signaling molecules. They are categorized into two groups based on their structure. These are integral transmembrane proteins and integral monotopic proteins.

Integral transmembrane proteins are those that span the entire cell membrane. These proteins can cross the membrane once or several times, intertwining in the phospholipid bilayer so that there are several pieces of the protein protruding through the cell wall. Overall, this is the most common type of ME.

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Examples of integral transmembrane proteins include voltage-gated ion channels, such as those that transport potassium ions into and out of cells. Certain types of T cell receptors, the insulin receptor and many other receptors and neurotransmitters, are all integral transmembrane proteins. In general, receptors, transmitters, and transporters tend to belong to this class of IMPs because proteins that span the entire membrane are typically able to sense conditions both inside and outside the cell simultaneously.

Integral monotopic proteins do not span the entire biological membrane. Instead, they are attached to the membrane on one side only, with one end of the protein protruding inside or outside the cell. This class of proteins includes enzymes such as monoamine oxidase and fatty acid amide hydrolase. Integral monotopic proteins are unable to detect conditions inside and outside the cell and are less likely to be involved in intercellular signaling.

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