In biology, caveolae, which are a special type of lipid raft, are small invaginations of the plasma membrane in the cells of many vertebrates. They are the most abundant surface feature of many vertebrate cell types, especially endothelial cells, adipocytes and embryonic notochord cells. They were originally discovered by E. Yamada in 1955.
The plasma membranes of cells contain combinations of glycosphingolipids, cholesterol and protein receptors organised in glycolipoprotein lipid microdomains termed lipid rafts. Their existence in cellular membranes remains controversial. Indeed, Kervin and Overduin imply that lipid rafts are misconstrued protein islands, which they propose form through a proteolipid code. Nonetheless, it has been proposed that they are specialized membrane microdomains which compartmentalize cellular processes by serving as organising centers for the assembly of signaling molecules, allowing a closer interaction of protein receptors and their effectors to promote kinetically favorable interactions necessary for the signal transduction. Lipid rafts influence membrane fluidity and membrane protein trafficking, thereby regulating neurotransmission and receptor trafficking. Lipid rafts are more ordered and tightly packed than the surrounding bilayer, but float freely within the membrane bilayer. Although more common in the cell membrane, lipid rafts have also been reported in other parts of the cell, such as the Golgi apparatus and lysosomes.
Lipid signaling, broadly defined, refers to any biological cell signaling event involving a lipid messenger that binds a protein target, such as a receptor, kinase or phosphatase, which in turn mediate the effects of these lipids on specific cellular responses. Lipid signaling is thought to be qualitatively different from other classical signaling paradigms because lipids can freely diffuse through membranes. One consequence of this is that lipid messengers cannot be stored in vesicles prior to release and so are often biosynthesized "on demand" at their intended site of action. As such, many lipid signaling molecules cannot circulate freely in solution but, rather, exist bound to special carrier proteins in serum.
Aquaporin 3 (AQP-3) is the protein product of the human AQP3 gene. It is found in the basolateral cell membrane of principal collecting duct cells and provides a pathway for water to exit these cells. Aquaporin-3 is also permeable to glycerol, ammonia, urea, and hydrogen peroxide. It is expressed in various tissues including the skin, respiratory tract, and kidneys as well as various types of cancers. In the kidney, aquaproin-3 is unresponsive to the antidiuretic hormone vasopressin, unlike aquaporin-2. This protein is also a determinant for the GIL blood group system.
Lipopolysaccharide binding protein (LBP) is a protein that in humans is encoded by the LBP gene.
Caveolin-1 is a protein that in humans is encoded by the CAV1 gene.
Calcitonin receptor-like (CALCRL), also known as the calcitonin receptor-like receptor (CRLR), is a human protein; it is a receptor for calcitonin gene-related peptide.
Ephrin B1 is a protein that in humans is encoded by the EFNB1 gene. It is a member of the ephrin family. The encoded protein is a type I membrane protein and a ligand of Eph-related receptor tyrosine kinases. It may play a role in cell adhesion and function in the development or maintenance of the nervous system.
Melanotransferrin is a protein that in humans is encoded by the MFI2 gene. MFI2 has also recently been designated CD228.
Wiskott–Aldrich syndrome protein family member 2 is a protein that in humans is encoded by the WASF2 gene.
Lysophosphatidic acid receptor 2 also known as LPA2 is a protein that in humans is encoded by the LPAR2 gene. LPA2 is a G protein-coupled receptor that binds the lipid signaling molecule lysophosphatidic acid (LPA).
Collagen alpha-3(IV) chain is a protein that in humans is encoded by the COL4A3 gene.
Flotillin-1 is a protein that in humans is encoded by the FLOT1 gene.
Mannose-6-phosphate receptor binding protein 1 (M6PRBP1) is a protein which in humans is encoded by the M6PRBP1 gene. Its gene product, as well as the gene itself, is commonly known as TIP47.
Retinol binding protein 1, cellular, also known as RBP1, is a protein that in humans is encoded by the RBP1 gene.
Prion protein 2 (dublet), also known as PRND, or Doppel protein, is a protein which in humans is encoded by the PRND gene.
Lipid phosphate phosphohydrolase 1 also known as phosphatidic acid phosphatase 2a is an enzyme that in humans is encoded by the PPAP2A gene.
Pancreatic secretory granule membrane major glycoprotein GP2 is a protein that in humans is encoded by the GP2 gene.
Caveolin-2 is a protein that in humans is encoded by the CAV2 gene.
Laminin subunit gamma-3 also known as LAMC3 is a protein that in humans is encoded by the LAMC3 gene.
