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Publication Abstract from PubMed

In our continued investigations of microbial globins, we solved the structure of a truncated hemoglobin from Shewanella benthica, an obligate psychropiezophilic bacterium. The distal side of the heme active site is lined mostly with hydrophobic residues, with the exception of a tyrosine, Tyr34 (CD1) and a histidine, His24 (B13). We found that purified SbHbN, when crystallized in the ferric form with polyethylene glycol as precipitant, turned into a green color over weeks. The electron density obtained from the green crystals accommodated a trans heme d, a chlorin-type derivative featuring a gamma-spirolactone and a vicinal hydroxyl group on a pyrroline ring. In solution, exposure of the protein to one equivalent of hydrogen peroxide resulted in a similar green color change, but caused by the formation of multiple products. These were oxidation species released on protein denaturation, likely including heme d, and a species with heme covalently attached to the polypeptide. The Tyr34Phe replacement prevented the formation of both heme d and the covalent linkage. The ready modification of heme b by SbHbN expands the range of chemistries supported by the globin fold and offers a route to a novel heme cofactor.

Heme d formation in a Shewanella benthica hemoglobin.,Martinez Grundman JE, Schultz TD, Schlessman JL, Liu K, Johnson EA, Lecomte JTJ J Inorg Biochem. 2024 Jun 27;259:112654. doi: 10.1016/j.jinorgbio.2024.112654. PMID:38959524^[1]

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