Journal of the American Chemical Society, Vol.138, No.31, 9755-9758, 2016
Organometallic Complex Formed by an Unconventional Radical S-Adenosylmethionine Enzyme
Pyrococcus horikoshii Dph2 (PhDph2) is an unusual radical S-adenosylmethionine (SAM) enzyme involved in the first step of diphthamide biosynthesis. It catalyzes the reaction by cleaving SAM to generate a 3-amino-3-carboxypropyl (ACP) radical. To probe the reaction mechanism, we synthesized a SAM analogue (SAMcA), in which the ACP group of SAM is replaced with a 3-carboxyally1 group. SAMcA. is cleaved by PhDph2, yielding a paramagnetic (S = 1/2) species, which is assigned to a complex formed between the reaction product, alpha-sulfinyl-3-butenoic acid, and the [4Fe-4S] cluster. Electron nuclear double resonance (ENDOR) measurements with C-13 and H-2 isotopically labeled SAM(CA) support a sr-complex between the C=C double bond of asulfinyl-3-butenoic acid and the unique iron of the [4Fe-4S] cluster. This is the first example of a radical SAM-related [4Fe-4S](+) cluster forming an organometallic complex with an alkene, shedding additional light on the mechanism of PhDph2 and expanding our current notions for the reactivity of [4Fe-4S] clusters in radical SAM enzymes.