Iron-Dependent Regulation of Molybdenum Cofactor Biosynthesis Genes in Escherichia coli

Abstract

Molybdenum cofactor (Moco) biosynthesis is a complex process that involves the coordinated function of several proteins. In recent years it has become obvious that the availability of iron plays an important role in the biosynthesis of Moco. First, the MoaA protein binds two [4Fe-4S] clusters per monomer. Second, the expression of the moaABCDE and moeAB operons is regulated by FNR, which senses the availability of oxygen via a functional [4Fe-4S] cluster. Finally, the conversion of cyclic pyranopterin monophosphate to molybdopterin requires the availability of the l-cysteine desulfurase IscS, which is a shared protein with a main role in the assembly of Fe-S clusters. In this report, we investigated the transcriptional regulation of the moaABCDE operon by focusing on its dependence on cellular iron availability. While the abundance of selected molybdoenzymes is largely decreased under iron-limiting conditions, our data show that the regulation of the moaABCDE operon at the level of transcription is only marginally influenced by the availability of iron. Nevertheless, intracellular levels of Moco were decreased under iron-limiting conditions, likely based on an inactive MoaA protein in addition to lower levels of the l-cysteine desulfurase IscS, which simultaneously reduces the sulfur availability for Moco production. IMPORTANCE FNR is a very important transcriptional factor that represents the master switch for the expression of target genes in response to anaerobiosis. Among the FNR-regulated operons in Escherichia coli is the moaABCDE operon, involved in Moco biosynthesis. Molybdoenzymes have essential roles in eukaryotic and prokaryotic organisms. In bacteria, molybdoenzymes are crucial for anaerobic respiration using alternative electron acceptors. This work investigates the connection of iron availability to the biosynthesis of Moco and the production of active molybdoenzymes.

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“…The moaABCDE operon is involved in the Molybdenum cofactor (Moco) biosynthesis. This cofactor serves as the catalytic centre of Molybdoenzymes that are essential for anaerobic respiration (Zupok et al, 2019). Similarly, the uvrC gene increased the fitness of 4/74 in all environments except in InSPI2 ( Figure 10 ).…”

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“… 94 In E. coli , Fe-S cluster insertion to MoaA is mediated by the Isc system and an A-type carrier protein ErpA under oxygen-limiting condition. 95 E. coli grown under iron limiting conditions show significantly reduced intracellular Moco production due to the dysfunctional [4Fe-4S] assembly and failure to produce functional MoaA and the downregulation of l -cysteine desulfurase essential for MPT synthase 96 ( Figure 1 ). Therefore, specific inhibition of Fe-S cluster biosynthesis or sulfur trafficking in pathogenic bacteria may provide potent growth inhibition by pleiotropic loss of both FeS cluster and Moco.…”

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“…In E. coli, transcription of the moaABCDE operon is also upregulated by FNR (fumarate and nitrate reduction regulatory protein) (Anderson et al, 2000;Zupok et al, 2019a). FNR is a transcriptional regulator that is essential for expressing anaerobic respiratory processes (Unden et al, 2002).…”