Monothiol Glutaredoxins Grx3/4 and the BolA Protein Bol2 Modulate Iron Sensing and Regulation in Yeast S. cerevisiae

An elaborate cascade of iron‐sulfur cluster‐dependent cellular interactions are employed in the yeast S. cerevisiae in order to maintain adequate iron levels. Currently available data indicate that under iron deplete conditions, the two paralogous transcription factors, Aft1 and Aft2, are primarily localized in the nucleus, and activate the transcription of iron uptake and transport genes. Under iron replete conditions, Aft1/2 undergo conformational changes and nucleocytoplasmic shuttling upon interacting with CGFS monothiol glutaredoxins Grx3 and Grx4 and the BolA protein Bol2, resulting in subsequent deactivation of the iron regulon. Iron‐sulfur clusters have been chosen by nature as signaling molecules to accomplish the inhibition of Aft2 (and presumably Aft1), as the dimerization occurs via direct ligation of a [2Fe‐2S] cluster acquired from the [2Fe‐2S] cluster‐bridged Grx3/4‐Bol2 heterodimer. However, the mechanistic details of iron regulation at the molecular level in the baker's yeast are not fully understood, and defining the functional interactions of each component in the iron signaling pathway remains to be elucidated. We are currently using complementary biophysical and molecular genetic methods to probe the iron‐sulfur cluster‐dependent interaction between [2Fe‐2S] 2+ ‐Grx3/4 and Bol2, and [2Fe‐2S] 2+ ‐Grx3/4‐Bol2 and Aft2 to gain a better understanding of their in vivo functions. The results indicate rapid interaction between [2Fe‐2S] 2+ ‐Grx3 and Bol2, followed by a fast iron‐sulfur cluster transfer to Aft2, with second order rates above previously reported rates for reactions involving iron‐sulfur clusters. Furthermore, we are showing that mutations in the amino acid residues ligating the iron‐sulfur cluster in the [2Fe‐2S] 2+ ‐Grx3‐Bol2 heterodimer, or in the CxC iron‐sulfur cluster binding motif of Aft2 have a significant impact on the rate of interaction and cluster transfer, respectively. Since several key proteins in this pathway are conserved in humans and essential for viability, exploiting the yeast system to define their functional and physical interactions will provide a fundamental understanding of their roles in human iron metabolism. Support or Funding Information National Institute of General Medical Sciences R01 (Grant GM100069 to CEO) This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .