The lumazine synthase-riboflavin synthase complex of Bacillus subtilis. Crystallization of reconstituted icosahedral beta-subunit capsids.

Abstract

The lumazine synthase-riboflavin synthase complex (heavy riboflavin synthase) of Bacillus subtilis consists of an icosahedral capsid of 60 beta-subunits containing a core of three alpha-subunits. The enzyme has been purified from the derepressed mutant H 94 of B. subtilis by a novel efficient procedure using column chromatography and preparative crystallization. Beta-Subunits were isolated after dissociation of the enzyme at pH 8.0. Ligand-driven renaturation of beta-subunits yields hollow icosahedral beta 60 capsids which could be crystallized in 1.55 M phosphate, pH 8.7, in three different modifications. A monoclinic modification belongs to space group C2 with unit cell dimensions of a = 235.5, b = 191.2, and c = 165.4 A and alpha = gamma = 90 degrees and beta = 134.4 degrees. The crystals contain two hollow beta 60 particles/unit cell and diffract to approximately 2.8-A resolution. A hexagonal modification has the space group P6(3)22 with unit cell dimensions of a = b = 157.2 and c = 300.8 A and alpha = beta = 90 degrees and gamma = 120 degrees. These cell parameters are similar to the dimensions of hexagonal crystals of native heavy riboflavin synthase (alpha 3 beta 60). A second hexagonal modification shows unit cell parameters of a = b = 156.3 and c = 622.6 A and alpha = beta = 90 degrees and gamma = 120 degrees. The space group of this modification could not be determined unambiguously.