Fe(III) – Sulfide interaction in globins: Characterization and quest for a putative Fe(IV)-sulfide species

Mycobacterium tuberculosis DosS binds H2S through its Fe3+ heme iron to regulate the Dos dormancy regulon

“…Our spectroscopic data also show that binding of sulfide does not alter the oxidation state of DosS ferric heme iron, and that direct H2S binding to the ferric iron changes its spin state from high to low. Our findings are consistent with several reports showing that sulfide reacts with heme iron in the ferric (Fe 3+ ) state (15)(16)(17)(18)(19). This may allow induction of the Dos regulon at earlier stages of infection prior to the onset of hypoxia when ferrous DosS can respond to NO and CO only.…”

“…Nonetheless, our EPR and UV-Vis spectroscopy data spectroscopy provide compelling evidence that DosS heme is in the ferric state (Fig 1B and 1D). Also, our data showing that DosS can only bind H 2 S in the met (Fe 3+ ) state is consistent with numerous studies demonstrating that ferric, but not ferrous heme iron in proteins binds H 2 S (15, 16, 18, 45).…”

“…Using the maximum change in absorbance at ~408 nm, we generated a substrate saturation curve from which a KD app value of 5.64 ± 0.27 µM was calculated for H2S binding to DosS (3B and Inset). Notably, this KD app value is similar to the KD app value of 7.0 ± 0.4 µM reported for the H2S-met hemoglobin complex (15,18). In summary, these results show that measureable, direct binding of H2S to DosS (Fe 3+ ) does not reduce DosS to the active Fe 2+ form.…”

“…While H2S can chemically modify biomolecules directly (12)(13)(14), we considered the possibility that alterations in gene expression in response to H2S are mediated by regulatory proteins in Mtb. Since H2S is known to bind the iron in heme-containing proteins (15)(16)(17)(18)(19), and because DosS was among the Dos regulon genes induced upon exposure to H2S (7), we hypothesize that DosS and/or DosT sense and respond to H2S to induce the Dos dormancy regulon. To examine the interaction of H2S with DosS and DosT, we used UV-visible and EPR spectroscopy.…”

Redox control and autoxidation of class 1, 2 and 3 phytoglobins from Arabidopsis thaliana

“…The heme iron in globins can generally be cycled through ferrous (Hb-Fe 2+ ), ferric (Hb-Fe 3+ ) or ferryl (Hb-Fe 4+ ) oxidation states, with the less usual super-reduced iron and sulfo-ferryl forms proposed in special cases 54 , 55 . The midpoint redox potential for the Fe 3+ /Fe 2+ transition of the heme of AtHb1, AtHb2 and AtHb3 was determined by spectrophotometric titration with dithionite in the 5–10 pH range.…”