Mass spectrometric identification of intermediates in the O2-driven [4Fe-4S] to [2Fe-2S] cluster conversion in FNR

Jason C. Crack, Andrew J. Thomson, Nick E. Le Brun

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Abstract

The iron-sulfur cluster containing protein FNR is the master regulator for the switch between anaerobic and aerobic respiration in Escherichia coli and many other bacteria. The [4Fe-4S] cluster functions as the sensory module, undergoing reaction with O2 that leads to conversion to a [2Fe-2S] form with loss of high affinity DNA-binding. Here we report studies of the FNR
cluster conversion reaction using time-resolved electrospray ionization mass spectrometry. The data provide new insight into the reaction, permitting the detection of cluster conversion intermediates and products, including a novel [3Fe-3S] cluster and persulfide coordinated [2Fe-2S] clusters ([2Fe-2S](S)n, where n = 1 or 2). Analysis of kinetic data revealed a branched mechanism in which cluster sulfide oxidation occurs in parallel with cluster conversion, and not as a subsequent, secondary reaction, to generate ([2Fe-2S](S)n species.
This methodology shows great potential for broad application to studies of protein cofactorsmall molecule interactions.
Original languageEnglish
Pages (from-to)E3215–E3223
JournalProceedings of the National Academy of Sciences of the United States of America (PNAS)
Volume114
Issue number6
Early online date3 Apr 2017
DOIs
Publication statusPublished - 18 Apr 2017

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