Rhizobiales bear an atypical riboflavin biosynthetic pathway that would be involved in virulence and symbiosis. (Poster)

SEBASTIÁN KLINKE; HERNÁN R. BONOMI; VANESA ZYLBERMAN; FERNANDO A. GOLDBAUM

Steamboat Springs, Colorado, EEUU

Congreso; Structural Genomics and its Applications to Chemistry, Biology and Medicine; 2008

Keystone Symposia

Lumazine synthase catalyzes the penultimate step in the biosynthesis of riboflavin (vitamin B2) in plants, fungi and microorganisms. This enzyme shows different quaternary organizations between species, existing as pentamers, decamers or icosahedrally arranged dodecamers of pentamers. Interestingly, the pathogen Brucella and the symbiont Mesorhizobium (two members from the order Rhizobiales) encode two lumazine synthase isoenzymes named RibH1 (pentameric) and RibH2 (decameric) in their genomes. In this work we study the crystal structure and catalytic properties from RibH1 and RibH2 in both genera. Key differences observed in the active site architecture that affect substrate recognition are proposed as the basis for the highly variable enzymatic parameters determined for both isoenzymes, with the RibH2 proteins almost inactive. The question if both isoenzymes are really involved in the biosynthesis of riboflavin or if RibH2 may have evolved to harbor a yet undescribed function is discussed in terms of structural and biochemical approaches. This work was supported by a HHMI International Grant and by the Argentinian Science and Technology Agency.