{"class":"Secondary Metabolism","date_inserted":"2018-03-21T18:40:25.135Z","date_modified":"2018-03-21T18:40:25.135Z","description":"Mycosporines (mycosporine-like amino acids [MAAs]) are a diverse family of UV-absorbing secondary\r\nmetabolites that serve as screens against high doses of UV radiation (UVR).  They are found in cyanobacteria, some eukaryotic algae, corals, and fungi. MAAs are water soluble and colorless\r\nand share a 5-dihydroxy, 5-hydroxymethyl, cyclohex-1, 2-ene ring, with a methoxy group at C-2. This core structure is substituted in C-3 with an amino compound (usually an amino acid or amino alcohol) to form oxomycosporines. Ketone replacement with a second amino compound defines the iminomycosporine group. MAAs present typical UV absorption spectra with a single, narrow, and strongly absorbing band that has a maximum around 310 nm for oxomycosporines and around 330 nm for simple iminomycosporines. These compounds\r\nprotect the cell by absorbing UVR and dissipating the energy as heat without generating reactive oxygen species. MAAs have found pharmaceutical and cosmetic applications for their ability to protect skin from UV-mediated damage. \r\nMAA biosynthesis starts from sedoheptulose-7-phosphate (SHP) in the Calvin-Benson-Bassham cycle that is processed by demethyl 4-deoxygadusol (DDG) synthase and O-methyltransferase (O-MT), respectively, to form 4-deoxygadusol (4-DG), the core structure of mycosporines, followed by addition of glycine to 4-DG to form mycosporine-glycine and further condensation of serine to yield shinorine.\r\n \r\n","id":"00c2c133-a6a9-47d1-99c1-b6a451b65fd0","subsystem_id":"Mycosporine_synthesis_cluster","subsystem_name":"Mycosporine synthesis cluster","superclass":"Metabolism","role_name":["Demethyl 4-deoxygadusol synthase MysA","O-methyltransferase MysB","ATP-grasp ligase forming mycosporine-glycine, MysC","Predicted sodium/serine symporter MysT","D-alanine--D-alanine ligase (EC 6.3.2.4) MysD","Mycosporine-producing nonribosomal peptide synthetase"],"notes":["MycA = NpR5600 in N. punctiforme and its homologue Ava_3858 in Anabaena variabilis, encode demethyl 4-deoxygadusol (DDG) synthase, a sugar phosphate cyclase which acts on sedoheptulose 7-phosphate as a substrate. \r\nMycB = NpR5599 and its homologue Ava_3857 code for O-methyltransferases that catalyze the methylation of DDG, giving 4-deoxygadusol. \r\nMysC = product of NpR5598 can catalyze the condensation of glycine onto DG to produce mycosporine-glycine. \r\nMysD = NpF5597 belongs to the ATP-dependent carboxylate-amine-thiol ligase superfamily (ATP-grasp ligases). It most likely  phosphorylates mycosporine-glycine, as a means of activation to allow the addition of the L-serine to the activated cyclohexone core, with the concurrent formation of water, ADP, and Pi. This has to be regarded as a working hypothesis.\r\n\r\nMycT = co-ocures with MycABC and is predicted in this SS to be a sodium/serine symporter.\r\n\r\nWhile functionally analogous, Ava_3855 and NpF5597 are entirely distinct proteins in sequence, functional domain, and, likely, also in mechanism. The reaction catalyzed by Ava_3855 involves the activation of the serine carboxylate, adenylation, and loading by the adenylation domain, which activates the amino acid as aminoacyl-AMP. Subsequently, the activated amino acid is transferred to the 4-phosphopantetheine moiety of the thiolation domain (T-domain) or peptidyl carrier protein (PCP) domain with the release of AMP. Ava_3855 thus functionally belongs together with many nonribosomal\r\npeptide synthetases (NRPSs).\r\n"],"role_id":["Demethyl 4-deoxygadusol synthase MysA","O-methyltransferase MysB","ATP-grasp ligase forming mycosporine-glycine, MysC","Predicted sodium/serine symporter MysT","D-alanine--D-alanine ligase (EC 6.3.2.4) MysD","Mycosporine-producing nonribosomal peptide synthetase"],"pmid":["21963801","21890703"],"_version_":1809284005070110700}