Protein secretion, functional

Semaphorins are secreted, membrane-associated or transmembrane proteins defined by the presence of a sema-phorin protein domain (Serna domain). In the mammalian system, more than 20 semaphorins have been identified which play important roles in a variety of tissues. The best characterized receptors for mediating semaphoiin effects are members of the neuropilin and plexin families of transmembrane proteins. Semaphoiin functions are best described in the regulation of neural development, angiogenesis, immunoregulation and cancer. 

It is now recognised that the function of the immune system is carefully regulated by cytokines, small (8.5-40 kDa) proteins secreted by immune cells and by tissue cells such as endothelial cells and fibroblasts. T helper cells and macrophages are major sources of cytokines during inflammatory... 

Young, G. M., Schmiel, D. H., and Miller, V. L. (1999). A new pathway for the secretion of virulence factors by bacteria the flagellar export apparatus functions as a protein-secretion system. Proc. Natl. Acad. Sci. U.S.A. 96, 6456-6461. 

The interferons are a family of proteins secreted by animal cells in response to viral and parasitic infections, and are part of the host s defence mechanism. They display multiple activities, affecting the functioning of the immune system, cell proliferation, and cell differentiation, primarily by inducing the synthesis of other proteins. Accordingly, they have potential as antiviral, antiprotozoal, immunomodulatory, and cell growth regulatory agents. 

The anterior surface of the eye is constantly rinsed by tear fluid secreted at a flow rate of about 1 pL/min by the main lachrymal gland of the lachrymal apparatus. Tears eventually drain into the nasal cavity through the nasolachrymal ducts. Tear fluid contains mucin, lysozyme, lactoferrin, prealbumin, and serum proteins. It functions as an antibacterial lubricant and aids in draining out foreign substances. The normal volume of tear fluid is 5 to 10 xL.66... 

The aquaporins are a family of small, integral membrane proteins that function as plasma membrane transporters of water and in some cases small polar solutes. There are at least 10 distinct aquaporins in mammals with specific expression patterns in epithelial, endothelial, and other tissues. Studies in aquaporin-null mice indicated a key role for aquaporins in the urinary concentrating mechanism, fluid secretion of glands, brain swelling, skin moisture, hearing and vision, and gastrointestinal absorption.62... 

Helical cytokines are secreted proteins that function as intracellular messengers. The information content contained on their a-helical scaffolds is decoded by extracellular high-fidelity interactions with cell surface receptor chains that initiate intracellular signaling cascades leading to diverse cellular functions. Amino acid sequence analysis of the extracellular cytokine binding domains revealed two distinct receptor subclasses, class-1 and class-2 (Bazan, 1990a,b). The a-helical cytokines were subsequently defined based on the class of receptor (class 1 or class 2) they... 

Phosphatidylinositol 4-phosphate (PI-4-P, 3) is the second most abundant inositol phospholipid in biological membranes. It is a product of phosphorylation by four different species of PI 4-kinases (21), and it is a precursor to PI-4,5-P2 and PI-3,4,5-P3. These kinases are the two inositol lipids whose biological roles are understood best. The biological function of PI-4-P is not well known however, the studies in yeast indicate its role extends beyond the substrate for PI 5-kinase (21), such as regulation of vesicular trafficking and protein secretion from Golgi. PI-4-P is removed by the subsequent phosphorylation to PI-4,5-P2 or dephosphorylation to PI by ER-localized phosphatase (21). 

Cytokines are regulatory proteins secreted primarily by white blood cells but also by a variety of other cells in the body their functions include numerous effects on cells of the immune system and inflammatory processes (Vilcek, 2003). Most cytokines are single polypeptide chains, although they may form mul timers in biological fluids. As an exceptionally large and diverse group of factors, cytokines... 

Mitochondria 39% 18-22% 1,700-2,200 Protein secretion, haem synthesis, transport and degradation functions, cellular energy generation (ATP), oxidative phosphorylation, urea synthesis, gluconeogenesis, liponeogenesis, ketogenesis, p-oxidation of fatty acids, citric acid cycle, respiratory chain, etc. 

Rat a2-gIobulin (A2U) and the homologous mouse protein (major urinary protein, MUP) are the principal proteins secreted in the urine of male rodents. Because male urine affects the behavior and sexual response of females, it has been suggested that these proteins function as pheromone-binding proteins. The crystal structures of both proteins have been determined (Bocskei et al., 1992). As expected (Cowan et al, 1990), both structures have the RBP fold. The Ca coordinates of the /3 barrel agree with an RMS difference of approximately 1.2 A. Both contain a ligand in the center of the barrel, where extensive interactions are made with the hydrophobic residues lining the barrel. For the MUP... 

Grimmond SM, Miranda KC, Yuan Z, et al. The mouse secretome Functional classification of the proteins secreted into the extracellular environment. Genome Res. 2003 13 1350-1359. 

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