About Lipocalin / LCN:
The lipocalin family refers to a group of extracellular proteins. These proteins display much diversity within the sequence level. Lipocalins transport hydrophobic molecules such as lipids, retinoids, steroids and bilins. Lipocalins share regions of sequence homology; in a common structure of an antiparallel beta-barrel made up of eight strands. Fatty acid proteins exploit the beta-barrel fold, also working to bind hydrophobic molecules. Lipocalin proteins have been found in plants, invertebrate cells, vertebrate cells and also in gram-negative bacteria. Most lipocalins function to transfer or to store compounds which are chemically sensitive.
Analysis of lipocalins exemplifies that the entire family are made up of proteins that are related closely. These proteins include the outlier lipocalins, the kernel lipocalins and a few other varying sequences. Kernel lipocalins form the most extensive set within the related sequences. When lipocalins are engineered to make a modification to their binding properties; they are then classed as anticalins.
The functions of lipocalin proteins are cryptic coloration, cell regulation, nutrient transportation, pheromone transportation and the synthesis of prostaglandins. One example being, a retinol-binding protein which works to transport retinol from the liver into the peripheral tissues. Another basic function of lipocalins is to bind hydrophobic ligands. As extracellular proteins, lipocalins work as carriers for the ligands.
Lipocalin is associated with the detoxification and inflammation procedures caused by the activation of the immune system within mammals. These are considered to be allergens in a respiratory sense for dogs, cats, horses and rodents. Some specific lipocalin proteins which are present in such responses are C8 Gamma or alpha-1-acid glycoprotein.
Lipocalin is associated with transporting the pheromones of mammals. Lipocalins are carriers of critical pheromones found in the mucus of rodents, for instance. One subfamily of lipocalin are urinary proteins; found in rodent urine and which also potentially act as protein pheromones.
Lipocalin can be found in tears and works to sequester cholesterol, glycolipids or fatty acid. Lipid binding functions to encourage changes in protein. Claims have been made that lipocalin gains lipid via scavenging on the surface of the corneal. It’s further been stated that lipocalin may improve the balance and transportation of lipid present in the surface layer.
Lipocalins have also been found to play a vital role in the response of the immune system to a bacterial infection. These proteins are thought to play a role in various human diseases. Obesity has been linked to decreased levels of LCN13, for instance. In addition to this, lipocalin-13 has been discovered as an insulin sensitizer which can work to improve the intolerance of glucose.
Lipophilic ligands have been proven to have the ability to enter a cell; whereby they can function as tumor protease inhibitors. Over the last few years, results have determined that LCN2 (Lipocalin 2) functions in several different types of cancer. Lipocalin 2 has been shown to promote the metastasis of cancerous cells by preventing autodegradation.