The protein product of the Methanococcus jannaschii MJ1256 gene has been expressed in Escherichia coli, purified to homogeneity, and shown to be involved in coenzyme F-420 biosynthesis. The protein catalyzes the transfer of the 2-phospholactate moiety from lactyl (2) diphospho-(5')guanosine (LPPG) to 7,8-didemethyl-8-hydroxy-5-deazariboflavin (Fo) with the formation of the L-lactyl phosphodiester of 7,8-didemethyl-8-hydroxy-5-deazariboflavin (F-420-0) and GMP. On the basis of the reaction catalyzed, the enzyme is named LPPG:Fo 2-phospho-L-lactate transferase. Since the reaction is the fourth step in the biosynthesis of coenzyme F-420, the enzyme has been designated as CofD, the product of the cofD gene. The transferase requires Mg2+ for activity, and the catalysis does not appear to proceed via a covalent intermediate. To a lesser extent CofD also catalyzes a number of additional reactions that include the formation of Fo-P, when the enzyme is incubated with Fo and GDP, GTP, pyrophosphate, or tripolyphosphate, and the hydrolysis of F-420-0 to Fo. All of these side reactions can be rationalized as occurring by a common mechanism. CofD has no recognized sequence similarity to any previously characterized enzyme.
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