1rvv
From Proteopedia
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SYNTHASE/RIBOFLAVIN SYNTHASE COMPLEX OF BACILLUS SUBTILIS
Overview
The lumazine synthase/riboflavin synthase of Bacillus subtilis is a, bifunctional enzyme complex catalysing the formation of riboflavin from, 5-amino-6-(D-ribitylamino)-2,4(1H,3H)-pyrimidinedione and, L-3,4-dihydroxy-2-butanone-4-phosphate via 6,7-dimethyl-8-ribityllumazine., The complex is composed of 3 alpha (riboflavin synthase) subunits and 60, beta (lumazine synthase) subunits and has a relative mass of 1 MDa. The 60, beta subunits are arranged in an icosahedral capsid enclosing the alpha, trimer in the central core. The protein was crystallised, and an X-ray, structure of the icosahedral capsid was obtained at 3.3 A resolution with, a crystallographic R-factor of 0.33. Hollow, icosahedral capsids, consisting of 60 beta subunits can be obtained by inhibitor-driven, renaturation of isolated beta subunits. They catalyse the formation of, 6,7-dimethyl-8-ribityllumazine at the same rate as the native alpha 3 beta, 60 complex and can be crystallised in two different hexagonal and one, monoclinic form. Crystallographic intensity data of the monoclinic, crystals to a resolution of 2.4 A were obtained using synchrotron, radiation and an image plate detector system. The orientation of the, icosahedral molecules in the monoclinic cell was deduced by real space, vector search procedures from a 3.5 A Patterson map. Phases were, calculated from the model of the alpha 3 beta 60 protein and were extended, by cyclic averaging exploring the 30-fold redundancy of the electron, density. The 2.4 A map allowed us to refine the existing atomic model of, lumazine synthase. The refined model includes 154 amino acid residues, one, inhibitor molecule, 58 water molecules and one phosphate ion. Applying, non-crystallographic-symmetry restraints the crystallographic R-factor is, 16.7% for 100,092 reflections between 10 and 2.4 A. The chain folding of, the beta subunits is closely similar to the native alpha 3 beta 60 enzyme., The lumazine synthase bears resemblance to the sugar binding proteins. The, significantly higher resolution compared to the alpha 3 beta 60 structure, determination allows a detailed description of the substrate analogue, binding site. The environment of the, 5-nitro-6-(D-ribitylamino)-2,4(1H,3H)-pyrimidinedione inhibitor is, particularly rigid, and the chain segments involved in forming the active, site are highly conserved for lumazine synthases of different species. A, residual density feature in the final map is interpreted as a bound, phosphate which mimics the binding of the second substrate. We discuss the, reaction mechanism on this structural basis.
About this Structure
1RVV is a Single protein structure of sequence from Bacillus subtilis with PO4 and INI as ligands. Full crystallographic information is available from OCA.
Reference
Studies on the lumazine synthase/riboflavin synthase complex of Bacillus subtilis: crystal structure analysis of reconstituted, icosahedral beta-subunit capsids with bound substrate analogue inhibitor at 2.4 A resolution., Ritsert K, Huber R, Turk D, Ladenstein R, Schmidt-Base K, Bacher A, J Mol Biol. 1995 Oct 13;253(1):151-67. PMID:7473709
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