Myeloperoxidase (MPO) is a heme-containing enzyme belonging to the XPO subfamily of peroxidases. It is an abundant neutrophil and monocyte glycoprotein that catalyzes the hydrogen peroxide-dependent conversion of chloride, bromide, and iodide to multiple reactive species. Post-translational processing of MPO involves the insertion of a heme moiety and the proteolytic removal of both a propeptide and a 6 aa internal peptide. This results in a disulfide-linked dimer composed of a 60 kDa heavy and 12 kDa light chain that associate into a 150 kDa enzymatically active tetramer. The tetramer contains two heme groups and one disulfide bond between the heavy chains. Alternate splicing generates two additional isoforms of MPO, one with a 32 aa insertion in the light chain, and another with a deletion of the signal sequence and part of the propeptide. Human and mouse MPO share 87% aa sequence identity. MPO activity results in protein nitrosylation and the formation of 3-chlorotyrosine and dityrosine crosslinks. MPO is also associated with a variety of other diseases, and inhibits vasodilation in inflammation by depleting the levels of NO. Serum albumin functions as a carrier protein during MPO movement to the basolateral side of epithelial cells. MPO is stored in neutrophil azurophilic granules. Upon cellular activation, it is deposited into pathogen-containing phagosomes.
Non-regulatory myosin light chain required for proper formation and/or maintenance of myofibers, and thus appropriate muscle function.
Myocilin, also known as Trabecular meshwork-induced glucocorticoid response protein, MYOC and GLC1A, is a protein which contains oneolfactomedin-like domain. Myocilin / MYOC may participate in the obstruction of fluid outflow in the trabecular meshwork. Myocilin / MYOC is expressed in large amounts in various types of muscle, ciliary body, papillary sphincter, skeletal muscle, heart and other tissues. Myocilin / MYOC is expressed predominantly in the retina. In normal eyes, it is found in the inner uveal meshwork region and the anterior portion of the meshwork. In contrast, in many glaucomatous eyes, it is found in more regions of the meshwork and appeared more intensively than in normal eyes, regardless of the type or clinical severity of glaucoma. Defects in Myocilin / MYOC may contribute to primary congenital glaucoma type 3A (GLC3A). Defects in MYOC may also contribute to this phenotype via digenic inheritance. GLC3A is an autosomal recessive form of primary congenital glaucoma (PCG). PCG is characterized by marked increase of intraocular pressure at birth or early choldhood, large ocular globes (buphthalmos) and corneal edema.
Myozenins may serve as intracellular binding proteins involved in linking Z-disk proteins such as alpha-actinin, gamma-filamin, TCAP/telethonin, LDB3/ZASP and localizing calcineurin signaling to the sarcomere. Plays an important role in the modulation of calcineurin signaling. May play a role in myofibrillogenesis.
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