Focus on Molecules: Sulfotyrosine
Section snippets
Structure
Besides being a precursor for neurotransmitters, hormones and melanin, tyrosine is a non-essential amino acid that is utilized by the eukaryotic cell to synthesize proteins. Once incorporated into proteins, tyrosine can be post-translationally modified by virtue of its side chain hydroxyl group by nitration, phosphorylation and sulfation. While nitrotyrosine is synthesized through a non-enzymatic reaction, tyrosines are phosphorylated and sulfated through the action of kinases and
Function
Immunoblot analyses of bovine ocular tissues using the anti-sulfotyrosine antibody, PSG2, have revealed that proteins containing sulfotyrosine residues are present in the lens, cornea, iris, sclera, RPE, retina, vitreous, and aqueous humor with highest levels in the vitreous humor and lowest levels in the lens (Kanan et al., 2012). Immunohistochemical analyses of the mouse eye show that sulfotyrosine proteins are expressed in all tissues of the eye including cornea, sclera, choroid, Bruch's
Disease involvement
Sulfotyrosines have been identified in proteins that have been implicated in human diseases including age-related macular degeneration (AMD) and diabetes. In AMD, excessive activation of complement proteins is accompanied by the appearance of extracellular deposits called drusen that contain an abundance of the sulfotyrosine-containing protein vitronectin. One of the many functions of vitronectin is to modulate the activation of the complement system by associating with the complement complex
Future studies
Sulfotyrosines mediate interactions between proteins and other molecules and are therefore positioned to play significant roles in ocular biology. Current studies are aimed at identifying sulfotyrosine-containing proteins and their binding partners in the eye. Once identified, it will be possible to carry out functional studies of these protein complexes using mutation, knock-in, and knockout techniques the results of which will help improve our understanding of the roles that these proteins
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