Biochemistry. 2019 Nov 19;58(46):4641-4654. doi: 10.1021/acs.biochem.9b00841. Epub 2019 Nov 7.
New Insight into the Mechanism of Anaerobic Heme Degradation.Abstract
ChuW, ChuX, and ChuY are contiguous genes downstream from a single promoter that are expressed in the enteric pathogen Escherichia coli
O157:H7 when iron is limiting. These genes, and the corresponding
proteins, are part of a larger heme uptake and utilization operon that
is common to several other enteric pathogens, such as Vibrio cholerae. The aerobic degradation of heme has been well characterized in humans and several pathogenic bacteria, including E. coli
O157:H7, but only recently was it shown that ChuW catalyzes the
anaerobic degradation of heme to release iron and produce a reactive
tetrapyrrole termed "anaerobilin". ChuY has been shown to function as an
anaerobilin reductase, in a role that parallels biliverdin reductase.
In this work we have employed biochemical and biophysical approaches to
further interrogate the mechanism of the anaerobic degradation of heme.
We demonstrate that the iron atom of the heme does not participate in
the catalytic mechanism of ChuW and that S-adenosyl-l-methionine
binding induces conformational changes that favor catalysis. In
addition, we show that ChuX and ChuY have synergistic and additive
effects on the turnover rate of ChuW. Finally, we have found that ChuS
is an effective source of heme or protoporphyrin IX for ChuW under
anaerobic conditions. These data indicate that ChuS may have dual
functionality in vivo. Specifically, ChuS serves as a heme oxygenase
during aerobic metabolism of heme but functions as a cytoplasmic heme
storage protein under anaerobic conditions, akin to what has been shown
for PhuS (45% sequence identity) from Pseudomonas aeruginosa.
- PMID:
- 31652058
- DOI:
- 10.1021/acs.biochem.9b00841
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