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Publication Abstract from PubMed

Mycobacterium tuberculosis(Mtb), the causative agent of tuberculosis, requires iron for survival. In Mtb, MhuD is the cytosolic protein that degrades imported heme. MhuD is distinct, both in sequence and structure, from canonical heme oxygenases (HOs) but homologous with IsdG-type proteins. Canonical HO is found mainly in eukaryotes, while IsdG-type proteins are predominantly found in prokaryotes including pathogens. While there are several published structures of MhuD and other IsdG-type proteins in complex with heme substrate, no structures have been reported of IsdG-type proteins in complex with product, unlike HOs. We recently showed that the Mtb variant MhuD-R26S produces biliverdin IXalpha (alphaBV) rather than the wild-type mycobilin isomers as product. Given that mycobilin and other IsdG-type protein products like staphylobilin are difficult to isolate in quantities sufficient for structure determination, here we use the MhuD-R26S variant and its product alphaBV as a proxy to study the IsdG-type protein/product complex. First we show that alphaBV has nanomolar affinity for MhuD and the R26S variant. Second we determined the MhuD-R26S-BV complex structure to 2.5 A, which reveals two notable features (1) two alphaBV molecules bound per active site and (2) a novel alpha-helix (alpha3) unobserved in previous MhuD-heme structures. Finally, through molecular dynamics simulations we show that alpha3 is stable with the proximal alphaBV alone. With MhuD's high affinity for product along with observed structural and electrostatic changes that accompany substrate turnover suggest that there may be an unidentified class of proteins responsible for product extraction from MhuD and other IsdG-type proteins.

The structure of a Mycobacterium tuberculosis heme-degrading protein, MhuD, variant in complex with its product.,Chao A, Burley K, Sieminski PJ, de Miranda R, Chen X, Mobley DL, Goulding C Biochemistry. 2019 Oct 22. doi: 10.1021/acs.biochem.9b00726. PMID:31638374^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.