Characterization of [2Fe-2S] Clusters in Monothiol Glutaredoxin-BolA Complexes and ASP1 a Novel Phosphatase/Kinase

Iron sulfur clusters are common cofactors found in almost all living organisms. They have diverse biological functions, ranging from electron transfer and catalysis to regulation of gene expression and enzyme activity. Glutaredoxin (Grx) proteins are found in both eukaryotic and prokaryotic organisms.  One class, called monothiol Grxs, functions as carrier proteins for Fe-S cluster biosynthesis by virtue of their ability to bind [2Fe-2S] clusters at the interface of homodimers using the active site cysteine residues of the highly conserved CGFS motifs and two glutathiones.^[1] Monothiol Grxs can also form [2Fe-2S] cluster-bound heterodimer complexes with BolA proteins.^[1,2] In eukaryotes, the BolA proteins have been shown to function in sensing cytoplasmic Fe levels by assessing the extent of [2Fe-2S] cluster-loading of monothiol Grxs and in modulating the specificity of [2Fe-2S] cluster transfer from monothiol Grxs to acceptor apo-Fe-S proteins. However, the role of BolA proteins in prokaryotes has yet to be determined. In this work, two monothiol Grxs, Grx5 and Grx^nif, in the aerobic nitrogen fixing organism Azotobacter vinelandii (Av) have been purified and spectroscopically characterized as [2Fe-2S] cluster-containing homodimers. In addition, the ability of these two Grxs to interact with or form heterodimers with two Av BolA proteins have been investigated to assess the role of BolA proteins in prokaryotic organisms.

Asp1 is a dual-function phosphatase/kinase that regulates cell morphogenesis

in Schizosaccharomyces pombe. Using spectroscopic and analytical techniques, the phosphatase domain was found to contain a [2Fe-2S] cluster that inhibits phosphatase activity, thereby increasing net kinase activity.^[3] This is the first example of an Fe-S cluster-containing phosphatase and potential roles for the cluster in regulating kinase/phosphatase activity in Asp1 will be discussed.

References:

[1] Roret, T., Tsan, P., Couturier, J., Zhang, B., Johnson, M. K., Rouhier, N., Didierjean, C. (2014). Structural and Spectroscopic Insights into BolA-Glutaredoxin Complexes. Journal of Biological Chemistry, 289, 24588-24589.

[2] Dlouhy, A. C., Li, H., Albetel, A. N., Zhang, B., Mapolelo, D. T., Randeniya, S., Holland, A. A., Johnson, M. K., Outten, C. E. (2016). The Escherichia coli BolA Protein IbaG Forms a Histidine-Ligated [2Fe-2S]-Bridged Complex with Grx4. Biochemistry, 55 (49), 6869-6879.

[3] Wang, H., Nair, V. S., Holland, A. A., Capolicchio, S., Jessen, H. J., Johnson, M. K., Shears, S. B. (2015). Asp1 from Schizosaccharomyces pombe binds a [2Fe-2S]²⁺ cluster which inhibits inositol pyrophosphate 1-phosphatase activity. Biochemistry, 54 (42), 6462-6474.