title: Multiple assembly states of lumazine synthase: a model relating catalytic function and molecular assembly.
abstract: Lumazine synthases have been observed in the form of pentamers, dimers of pentamers, icosahedral capsids consisting of 60 subunits and larger capsids with unknown molecular structure. Here we describe the analysis of the assembly of native and mutant forms of lumazine synthases from Bacillus subtilis and Aquifex aeolicus at various pH values and in the presence of different buffers using small angle X-ray scattering and electron microscopy. Both wild-type lumazine synthases are able to form capsids with a diameter of roughly 160 A and larger capsids with diameters of around 300 A. The relative abundance of smaller and larger capsids is strongly dependent on buffer and pH. Both forms can co-exist and are in some cases accompanied by other incomplete or deformed capsids. Several mutants of the B. subtilis lumazine synthase, in which residues in or close to the active site were replaced, as well as an insertion mutant of A. aeolicus lumazine synthase form partially or exclusively larger capsids with a diameter of about 300 A. The mutations also reduce or inhibit enzymatic activity, suggesting that the catalytic function of the enzyme is tightly correlated with its quaternary structure. The data show that multiple assembly forms are a general feature of lumazine synthases.
authors.affiliation: Karolinska Institutet, Department of Biosciences, Center for Structural Biochemistry, S-14157 Huddinge, Sweden.
authors.forename: Xiaofeng
authors.initials: X
authors.lastname: Zhang
authors.forename: Petr V
authors.initials: PV
authors.lastname: Konarev
authors.forename: Maxim V
authors.initials: MV
authors.lastname: Petoukhov
authors.forename: Dmitri I
authors.initials: DI
authors.lastname: Svergun
authors.forename: Li
authors.initials: L
authors.lastname: Xing
authors.forename: R Holland
authors.initials: RH
authors.lastname: Cheng
authors.forename: Ilka
authors.initials: I
authors.lastname: Haase
authors.forename: Markus
authors.initials: M
authors.lastname: Fischer
authors.forename: Adelbert
authors.initials: A
authors.lastname: Bacher
authors.forename: Rudolf
authors.initials: R
authors.lastname: Ladenstein
authors.forename: Winfried
authors.initials: W
authors.lastname: Meining
mesh_terms: D001412:Bacillus subtilis / Q000201:enzymology*; D001419:Bacteria / Q000201:enzymology*; D002213:Capsid / Q000201:enzymology; D002384:Catalysis; D020285:Cryoelectron Microscopy; D006863:Hydrogen-Ion Concentration; D008958:Models, Molecular; D009097:Multienzyme Complexes / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D050505:Mutant Proteins / Q000648:ultrastructure; D009154:Mutation / Q000235:genetics; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism; D011621:Pteridines / Q000737:chemistry; D011994:Recombinant Proteins / Q000648:ultrastructure; D012542:Scattering, Radiation
chemical_list: D009097:Multienzyme Complexes; D050505:Mutant Proteins; D021122:Protein Subunits; D011621:Pteridines; D011994:Recombinant Proteins; C001061:6,7-dimethyl-8-ribityllumazine; C044822:6,7-dimethyl-8-ribityllumazine synthase