Protein Crystallography: Studies on the enzyme Lumazine Synthase from the bacterium Brucella spp. (Poster)

SEBASTIÁN KLINKE; VANESA ZYLBERMAN; BEATRIZ G. GUIMARÃES; BRADFORD C. BRADEN; FERNANDO A. GOLDBAUM

Pto. Madryn, Chubut

Congreso; Segunda Reunión de la Asociación Argentina de Cristalografía; 2006

Asociación Argentina de Cristalografía

The protein Lumazine Synthase (LS) is an enzyme that catalyses the penultimate step in thebiosynthesis of riboflavin (vitamin B2). It is found in plants, fungi and microorganisms showing different quaternary assemblies, although the main building block is always a homopentamer. To date, crystallographic X-ray structures of eight different LSs have been solved. The particle is found either as single pentamers or as dodecamers of pentamers with icosahedral 532 symmetry. We study this protein from the pathogenic bacterium Brucella spp., the agent of the disease brucellosis that affects livestock and humans. Genomic sequences of Brucella show the presence of two genes that codify for LSs, namely RibH1 and RibH2. In this work we present the structure of both enzymes bound to a substrate analogue inhibitor at 2,30Å and 2,90 Å respectively. Enzymatic analyses as well as lack of characteristic features in the active site of RibH2 lead to the conclusionthat the latter protein presents a different function in the bacterium, whereas RibH1 would be the actual LS in Brucella. Our analysis is complemented with structural and enzymatic studies on LSs from Mesorhizobium loti, a phylogenetic-related microorganism. Crystalline samples were prepared by the hanging drop vapor diffusion method and all structures were solved by the Molecular Replacement procedure with data collected at the D03B-MX1 protein crystallography beamline at the Laboratório Nacional de Luz Síncrotron (LNLS), Campinas, Brazil.