Poster abstracts

Poster number 18 submitted by Stephen Pearson

Molecular Understanding of the Substrate Binding Residue D398 in S. cerevisiae Atm1p

Stephen A. Pearson (Biophysics), James A. Cowan (Chemistry and Biochemistry, The Ohio State University)

Abstract:
Iron-sulfur (Fe-S) clusters are common cofactors found in essentially all living organisms. In humans, Fe-S clusters are made predominately in the mitochondria, but assembly machinery is also present in the cytosol [1]. However, when mitochondrial Fe-S cluster assembly is inhibited, some cytosolic Fe-S cluster proteins are not able to convert to their holo forms due to lack of cluster [2]. One hypothesis is that an Fe-S cluster precursor molecule is transported out of the mitochondria, but we believe this molecule to be the Fe-S cluster itself, coordinated to four glutathione molecules {[Fe2S2](GS)4} [1,3]. Through liposome transport studies, we have shown that ABC transporter S. cerevisiae Atm1p is able to transport [Fe2S2](GS)4 clusters [3]. Atm1p is a homolog of the human inner-mitochondrial membrane protein ABCB7. Recently the crystal structure of N. aromaticivorans Atm1p was solved with two oxidized glutathione molecules bound in the transport domain. The orientation of the oxidized glutathione molecules resembles the expected structure of the [Fe2S2](GS)4 cluster. Mutations in the binding pocket, among other areas, in ABCB7 result in X-linked sideroblastic anemia [4]. This may be caused by the inability of the protein to transport [Fe2S2](GS)4 clusters out of the mitochondria and into the cytosol.

References:
[1] Roualt, T.A. (2012) Biogenesis of iron-sulfur clusters in mammalian cells: new insights and relevance to human disease, Dis Model Mech. 5(2), 155–164.
[2] Miao, R., Kim, H., Koppolu, U.M.K., Ellis, E.A., Scott, R.A., and Lindahl, P.A. (2009) Biophysical Characterization of the Iron in Mitochondria from Atm1p-depleted Saccharomyces cerevisiae, Biochemistry 48(40), 9556–9568.
[3] Qi, W., Li, J., and Cowan, J.A. (2014) A structural model for glutathione-complexed
iron–sulfur cluster as a substrate for ABCB7-type transporters, Chem. Commun. 50, 3795-3799.
[4] Lee, J.Y., Yang, J.G., Zhitnitsky, D., Lewinson, O., and Rees, D.C. (2014) Nature 343, 1133-1137

Keywords: Metalloprotein, Structure, ABC Transporter