title: The lumazine synthase/riboflavin synthase complex: shapes and functions of a highly variable enzyme system.
abstract: The xylene ring of riboflavin (vitamin B2 ) is assembled from two molecules of 3,4-dihydroxy-2-butanone 4-phosphate by a mechanistically complex process that is jointly catalyzed by lumazine synthase and riboflavin synthase. In Bacillaceae, these enzymes form a structurally unique complex comprising an icosahedral shell of 60 lumazine synthase subunits and a core of three riboflavin synthase subunits, whereas many other bacteria have empty lumazine synthase capsids, fungi, Archaea and some eubacteria have pentameric lumazine synthases, and the riboflavin synthases of Archaea are paralogs of lumazine synthase. The structures of the molecular ensembles have been studied in considerable detail by X-ray crystallography, X-ray small-angle scattering and electron microscopy. However, certain mechanistic aspects remain unknown. Surprisingly, the quaternary structure of the icosahedral β subunit capsids undergoes drastic changes, resulting in formation of large, quasi-spherical capsids; this process is modulated by sequence mutations. The occurrence of large shells consisting of 180 or more lumazine synthase subunits has recently generated interest for protein engineering topics, particularly the construction of encapsulation systems.
authors.affiliation: Department of Bioscience and Nutrition, Karolinska Institutet NOVUM, SE-14183 Huddinge, Sweden. Rudolf.Ladenstein@ki.se
authors.forename: Rudolf
authors.initials: R
authors.lastname: Ladenstein
authors.forename: Markus
authors.initials: M
authors.lastname: Fischer
authors.forename: Adelbert
authors.initials: A
authors.lastname: Bacher
mesh_terms: D001105:Archaea / Q000201:enzymology; D001419:Bacteria / Q000201:enzymology; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000378:metabolism; D005658:Fungi / Q000201:enzymology; D009097:Multienzyme Complexes / Q000737:chemistry* / Q000378:metabolism*; D010944:Plants / Q000201:enzymology; D011621:Pteridines / Q000378:metabolism; D012256:Riboflavin / Q000096:biosynthesis; D012258:Riboflavin Synthase / Q000737:chemistry* / Q000378:metabolism*; D012568:Schizosaccharomyces / Q000737:chemistry / Q000378:metabolism
chemical_list: D029968:Escherichia coli Proteins; D009097:Multienzyme Complexes; D011621:Pteridines; C008297:lumazine; C044822:6,7-dimethyl-8-ribityllumazine synthase; D012258:Riboflavin Synthase; D012256:Riboflavin