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Integral monotopic proteins are permanently attached to the cell membrane from one side. [5] Three-dimensional structures of the following integral monotopic proteins have been determined: prostaglandin H2 syntheses 1 and 2 (cyclooxygenases) lanosterol synthase and squalene-hopene cyclase; microsomal prostaglandin E synthase
Membrane proteins fall into several broad categories depending on their location. Integral membrane proteins are a permanent part of a cell membrane and can either penetrate the membrane (transmembrane) or associate with one or the other side of a membrane (integral monotopic).
Depiction of the transmembrane proteins that make up tight junctions: occludin, claudins, and JAM proteins. Occludin was the first integral membrane protein to be identified. It has a molecular weight of ~60kDa. It consists of four transmembrane domains and both the N-terminus and the C-terminus of the protein are intracellular.
Ion channels are integral membrane proteins, typically formed as assemblies of several individual proteins. Such "multi-subunit" assemblies usually involve a circular arrangement of identical or homologous proteins closely packed around a water-filled pore through the plane of the membrane or lipid bilayer.
Illustration of a eukaryotic cell membrane Comparison of a eukaryotic vs. a prokaryotic cell membrane. The cell membrane (also known as the plasma membrane or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of a cell from the outside environment (the extracellular space).
Every carrier protein, especially within the same cell membrane, is specific to one type or family of molecules. GLUT1 is a named carrier protein found in almost all animal cell membranes that transports glucose across the bilayer. This protein is a uniporter, meaning it transports glucose along its concentration in a singular direction. It is ...
At the top level are all alpha proteins (domains consisting of alpha helices), all beta proteins (domains consisting of beta sheets), and mixed alpha helix/beta sheet proteins. While most proteins adopt a single stable fold, a few proteins can rapidly interconvert between one or more folds. These are referred to as metamorphic proteins. [5]
Claudins are a family of proteins which, along with occludin, are the most important components of the tight junctions (zonulae occludentes). [1] [2] Tight junctions establish the paracellular barrier that controls the flow of molecules in the intercellular space between the cells of an epithelium.