YlaN is an iron(II) binding protein that functions to relieve Fur-mediated repression of gene expression inStaphylococcus aureus

Abstract

AbstractIron (Fe) is a trace nutrient required by nearly all organisms. As a result of the demand for Fe and the toxicity of non-chelated cytosolic ionic Fe, regulatory systems have evolved to tightly balance Fe acquisition and usage while limiting overload. In most bacteria, including the mammalian pathogenStaphylococcus aureus, the ferric uptake regulator (Fur) is the primary transcriptional regulator that controls the transcription of genes that code for Fe uptake and utilization proteins. YlaN was demonstrated to be essential inBacillus subtilisunless excess Fe is added to the growth medium, suggesting a role in Fe homeostasis. Here, we demonstrate that YlaN is expendable inS. aureus; however, YlaN became essential upon Fe deprivation. A nullfurallele bypassed the essentiality of YlaN. The transcriptional response of Fur derepression resulted in a reprogramming of metabolism to prioritize fermentative growth over respiratory growth. The absence of YlaN diminished the derepression of Fur-dependent transcription during Fe limitation. Bioinformatic analyses suggest thatylaNwas recruited to Gram positive bacteria and once acquired was maintained in the genome as it co-evolved with Fur. Consistent with a role for YlaN in influencing Fur-dependent regulation, YlaN and Fur interactedin vivo. YlaN bound Fe(II)in vitrousing oxygen or nitrogen ligands with an association constant that is consistent with a physiological role in Fe sensing and/or buffering. These findings have led to a model wherein YlaN is an Fe(II) binding protein that influences Fur-dependent regulation through direct interaction.ImportanceIron (Fe) is an essential nutrient for nearly all organisms. If Fe homeostasis is not maintained, Fe can accumulate in the cytosol where it is toxic. Questions remain about how cells efficiently balance Fe uptake and usage to prevent imbalance. Iron uptake and proper metalation of proteins are essential processes in the mammalian bacterial pathogenStaphylococcus aureus. Understanding the gene products involved in Fe ion regulation, uptake, and usage, as well as the physiological adaptations thatS. aureususes to survive in Fe-depleted conditions, will provide insight into the role that Fe has in pathogenesis. These data will also provide insight into the selective pressures imparted by the mammalian host.