Physical and Functional Interactions of the E. coli Monothiol Glutaredoxin GrxD Suggest a Role in FeS Apoprotein Maturation (LB132)

The biosynthesis of iron sulfur (FeS) clusters is a highly coordinated process enabled by multi‐protein systems such as Isc and Suf in E. coli. Additional accessory factors including the monothiol glutaredoxin, GrxD, are located outside of these defined systems. GrxD has been proposed to function as a shuttle protein acting to transfer FeS clusters between scaffold and carrier proteins, although specific functional role remain unknown. We have previously linked GrxD in FeS client protein interactions with the radical SAM enzyme MiaB. To address these different hypotheses, we conducted an extensive survey for physical interaction of GrxD with a comprehensive set of FeS cluster biosynthesis factors including cysteine desulfurase components (IscS, SufSE), FeS scaffold (IscU, SufBC2D) , carrier proteins (IscA SufA, ErpA, NfuA), HscA, HscB and various FeS apoproteins. We have employed various methods, including affinity co‐purification, analytical gel filtration and surface plasmon resonance (SPR) to obtain interaction data. To date we have observed no physical interaction between GrxD and any FeS biosynthesis factor except the SufBC2D scaffold and the SufA carrier protein. With SufA a reproducible but extremely weak association is observed by SPR alone (KD >> 700 µM). In contrast we have observed specific interactions between GrxD and two radical SAM enzymes, MiaB (KD =12 µM) and BioB (KD =34 µM). These data strongly indicate a role for GrxD in FeS protein maturation or repair, working downstream of the Suf system Grant Funding Source : NIH award GM088196 to G.B