TAILIEUCHUNG - Báo cáo khoa học: Biosynthesis of riboflavin in Archaea 6,7-Dimethyl-8-ribityllumazine synthase of Methanococcus jannaschii

Heterologous expression of the putative open reading frame MJ0303 ofMethanococcus jannaschiiprovided a recombin-ant protein catalysing the formation of the riboflavin precursor, 6,7-dimethyl-8-ribityllumazine, by condensation of 5-amino-6-ribitylamino-2,4(1H,3H)-pyrimidinedione and 3,4-dihydroxy-2-butanone 4-phosphate. Steady state kinetic analysis at 37 C and pH indicated a catalytic rate of 11 nmolÆmg )1 Æmin )1 ;Kmvalues for 5-amino-6-ribitylamino-2,4(1H,3H)-pyrimidinedione and 3,4-dihydroxybutanone 4-phosphate were and 52lM, respectively | Eur. J. Biochem. 270 1025-1032 2003 FEBS 2003 doi Biosynthesis of riboflavin in Archaea 6 7-Dimethyl-8-ribityllumazine synthase of Methanococcus jannaschii Ilka Haase1 Simone Mỏrtl1 Peter Kohler2 Adelbert Bacher1 and Markus Fischer1 1Lehrstuhl fur Organische Chemie und Biochemie Technische Universitat Munchen Garching Germany 2Deutsche Forschungsanstalt fur Lebensmittelchemie Lichtenbergstr. 4 D-85747 Gacching Germany Heterologous expression of the putative open reading frame MJ0303 of Methanococcus jannaschii provided a recombinant protein catalysing the formation of the riboflavin precursor 6 7-dimethyl-8-ribityllumazine by condensation of 5-amino-6-ribitylamino-2 4 1H 3H -pyrimidinedione and 3 4-dihydroxy-2-butanone 4-phosphate. Steady state kinetic analysis at 37 C and pH indicated a catalytic rate of 11 nmol-mg_1-min-1 Km values for 5-amino-6-ribitylamino-2 4 1H 3H -pyrimidinedione and 3 4-dihydroxybutanone 4-phosphate were and 52 M respectively. The enzyme sediments at an apparent velocity of about 12 S. Sedimentation equilibrium analysis indicated a molecular mass around 1 MDa but was hampered by nonideal solute behaviour. Negative-stained electron micrographs showed predominantly spherical particles with a diameter of about 150 ỉy. The data suggest that the enzyme from M. jannaschii can form capsids with icosahedral 532 symmetry consisting of 60 subunits. Keywords Archaea Methanococcus jannaschii riboflavin biosynthesis lumazine synthase quaternary structure. Flavocoenzymes derived from riboflavin vitamin B2 structure 6 Fig. 1 serve as essential redox cofactors in all cells. Whereas the biosynthesis of the vitamin has been studied in considerable detail in eubacteria and yeasts reviewed in 1-3 little is known about its formation in Archaea. The initial step of riboflavin biosynthesis in eubacteria fungi and plants has been shown to involve the formation of 2 5-diamino-5-ribosylamino-4 3H -pyrimidinone 5 -phosphate .

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