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The Biosynthesis of the Thiazole Phosphate Moiety of Thiamin (Vitamin B 1 ): The Early Steps Catalyzed by Thiazole Synthase

2004; American Chemical Society; Volume: 126; Issue: 10 Linguagem: Inglês

10.1021/ja039616p

1943-2984

Pieter C. Dorrestein, Huili Huili, Sean V. Taylor, Fred W. McLafferty, Tadhg P. Begley,

Enzyme Structure and Function

Thiazole synthase (ThiG) catalyzes an Amadori-type rearrangement of 1-deoxy-d-xylulose-5-phosphate (DXP) via an imine intermediate. In support of this, we have demonstrated enzyme-catalyzed exchange of the C2 carbonyl of DXP. Borohydride reduction of the enzyme DXP imine followed by top-down mass spectrometric analysis localized the imine to lysine 96. On the basis of these observations, a new mechanism for the biosynthesis of the thiazole phosphate moiety of thiamin pyrophosphate in Bacillus subtilis is proposed. This mechanism involves the generation of a ketone at C3 of DXP by an Amadori-type rearrangement of the imine followed by nucleophillic addition of the sulfur carrier protein (ThiS-thiocarboxylate) to this carbonyl group.