SummaryFumarate hydratase (FH) is an enzyme of the tricarboxylic acid (TCA) cycle mutated in hereditary and sporadic cancers. Despite recent advances in understanding its role in tumorigenesis, the effects of FH loss on mitochondrial metabolism are still unclear. Here, we used mouse and human cell lines to assess mitochondrial function of FH-deficient cells. We found that human and mouse FH-deficient cells exhibit decreased respiration, accompanied by a varying degree of dysfunction of respiratory chain (RC) complex I and II. Moreover, we show that fumarate induces succination of key components of the iron-sulfur cluster biogenesis family of proteins, leading to defects in the biogenesis of iron-sulfur clusters that affect complex I function. We also demonstrate that suppression of complex II activity is caused by product inhibition due to fumarate accumulation. Overall, our work provides evidence that the loss of a single TCA cycle enzyme is sufficient to cause combined RC activity dysfunction.

Say “when”: Analysis of the biosynthetic gene cluster for the polyether antibiotic and anticancer agent salinomycin (1) shows that its core structure is synthesised by a nine‐multienzyme modular polyketide synthase. Deletion of the salC gene, which is required for oxidative cyclisation, has led to the detection of a novel metabolite whose structure reveals the timing of a key dehydration step.

A novel mechanism is proposed for ring formation in the biosynthetic pathway to thiotetronate antibiotics thiolactomycin and Tü 3010.

Following the in vivo investigation of thiotetronate assembly in Lentzea sp. and in S. thiolactonus NRRL 15439 (Havemann et al., Chem. Commun., 2017, DOI: 10.1039/c6cc09933e), the minimal set of genes required for thiolactomycin production was determined through heterologous expression and the mechanism for polyketide assembly was established in vitro through incubation of recombinant TlmB with its substrates in the presence of either nonhydrolysable or hydrolysable chemical probes. The results presented here constitute unequivocal evidence of enzymatic processing by an unusual iterative polyketide synthase.

Chemical 'chain termination' probes were utilised for the investigation of thiotetronate antibiotic biosynthesis in the filamentous bacteria Lentzea sp. and Streptomyces thiolactonus NRRL 15439. The use of these tools led to the capture of biosynthetic intermediates involved in the thiotetronate polyketide backbone assembly, providing first insights into substrate specificity and in vivo intermediate processing by unusual iterative synthases.