The flavohemoglobin Yhb1 is a new interacting partner of the heme transporter Str3

Abstract

AbstractNitric oxide (˙NO) is a free radical that induces nitrosative stress, which can jeopardize cell viability. Yeasts have evolved diverse detoxification mechanisms to effectively counteract ˙NO‐mediated cytotoxicity. One mechanism relies on the flavohemoglobin Yhb1, whereas a second one requires the S‐nitrosoglutathione reductase Fmd2. To investigate heme‐dependent activation of Yhb1 in response to ˙NO, we use hem1Δ‐derivative Schizosaccharomyces pombe strains lacking the initial enzyme in heme biosynthesis, forcing cells to assimilate heme from external sources. Under these conditions, yhb1+ mRNA levels are repressed in the presence of iron through a mechanism involving the GATA‐type transcriptional repressor Fep1. In contrast, when iron levels are low, the transcription of yhb1+ is derepressed and further induced in the presence of the ˙NO donor DETANONOate. Cells lacking Yhb1 or expressing inactive forms of Yhb1 fail to grow in a hemin‐dependent manner when exposed to DETANONOate. Similarly, the loss of function of the heme transporter Str3 phenocopies the effects of Yhb1 disruption by causing hypersensitivity to DETANONOate under hemin‐dependent culture conditions. Coimmunoprecipitation and bimolecular fluorescence complementation assays demonstrate the interaction between Yhb1 and the heme transporter Str3. Collectively, our findings unveil a novel pathway for activating Yhb1, fortifying yeast cells against nitrosative stress.