Expression and Characterization of Truncated Human Heme Oxygenase (hHO-1) and a Fusion Protein of hHO-1 with Human Cytochrome P450 Reductase

Angela Wilks, Paul R.Ortiz de Montellano, Stephen Matthew Black, Walter L. Miller

Research output: Contribution to journalArticle

104 Citations (Scopus)

Abstract

A human heme oxygenase (hHO-1) gene without the sequence coding for the last 23 amino acids has been expressed in Escherichia coli behind the pho A promoter. The truncated enzyme is obtained in high yields as a soluble, catalytically-active protein, making it available for the first time for detailed mechanistic studies. The purified, truncated hHO-1/heme complex is spectroscopically indistinguishable from that of the rat enzyme and converts heme to biliverdin when reconstituted with rat liver cytochrome P450 reductase. A self-sufficient heme oxygenase system has been obtained by fusing the truncated hHO-1 gene to the gene for human cytochrome P450 reductase without the sequence coding for the 20 amino acid membrane binding domain. Expression of the fusion protein in pCWori+ yields a protein that only requires NADPH for catalytic turnover. The failure of exogenous cytochrome P450 reductase to stimulate turnover and the insensitivity of the catalytic rate toward changes in ionic strength establish that electrons are transferred intramolecularly between the reductase and heme oxygenase domains of the fusion protein. The Vmax for the fusion protein is 2.5 times higher than that for the reconstituted system. Therefore, either the covalent tether does not interfere with normal docking and electron transfer between the flavin and heme domains or alternative but equally efficient electron transfer pathways are available that do not require specific docking.

Original languageEnglish (US)
Pages (from-to)4421-4427
Number of pages7
JournalBiochemistry
Volume34
Issue number13
DOIs
StatePublished - Sep 1 1995

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NADPH-Ferrihemoprotein Reductase
Heme Oxygenase-1
Fusion reactions
Heme Oxygenase (Decyclizing)
Electrons
Heme
Genes
Proteins
Biliverdine
Rats
Amino Acids
Tetherlines
Enzymes
NADP
Osmolar Concentration
Oxidoreductases
Ionic strength
Liver
Escherichia coli
Membranes

ASJC Scopus subject areas

  • Biochemistry

Cite this

Expression and Characterization of Truncated Human Heme Oxygenase (hHO-1) and a Fusion Protein of hHO-1 with Human Cytochrome P450 Reductase. / Wilks, Angela; Montellano, Paul R.Ortiz de; Black, Stephen Matthew; Miller, Walter L.

In: Biochemistry, Vol. 34, No. 13, 01.09.1995, p. 4421-4427.

Research output: Contribution to journalArticle

Wilks, Angela ; Montellano, Paul R.Ortiz de ; Black, Stephen Matthew ; Miller, Walter L. / Expression and Characterization of Truncated Human Heme Oxygenase (hHO-1) and a Fusion Protein of hHO-1 with Human Cytochrome P450 Reductase. In: Biochemistry. 1995 ; Vol. 34, No. 13. pp. 4421-4427.
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