TY  - JOUR
A1  - Bühning, Martin
A1  - Friemel, Martin
A1  - Leimkühler, Silke
T1  - Functional Complementation Studies Reveal Different Interaction Partners of Escherichia coil IscS and Human NFS1
JF  - Biochemistry
N2  - The trafficking and delivery of sulfur to cofactors and nucleosides is a highly regulated and conserved process among all organisms. All sulfur transfer pathways generally have an L-cysteine desulfurase as an initial sulfur mobilizing enzyme in common, which serves as a sulfur donor for the biosynthesis of sulfur-containing biomolecules like iron sulfur (Fe-S) clusters, thiamine, biotin, lipoic acid, the molybdenum cofactor (Moco), and thiolated nucleosides in tRNA. The human L-cysteine desulfurase NFS1 and the Escherichia coli homologue IscS share a level of amino acid sequence identity of similar to 60%. While E. coli IscS has a versatile role in the cell and was shown to have numerous interaction partners, NFS1 is mainly localized in mitochondria with a crucial role in the biosynthesis of Fe-S clusters. Additionally, NFS1 is also located in smaller amounts in the cytosol with a role in Moco biosynthesis and mcm(5)s(2)U34 thio modifications of nucleosides in tRNA. NFS1 and IscS were conclusively shown to have different interaction partners in their respective organisms. Here, we used functional complementation studies of an E. coli iscS deletion strain with human NFS1 to dissect their conserved roles in the transfer of sulfur to a specific target protein. Our results show that human NFS1 and E. coli IscS share conserved binding sites for proteins involved in Fe-S cluster assembly like IscU, but not with proteins for tRNA thio modifications or Moco biosynthesis. In addition, we show that human NFS1 was almost fully able to complement the role of IscS in Moco biosynthesis when its specific interaction partner protein MOCS3 from humans was also present.
Y1  - 2017
U6  - https://doi.org/10.1021/acs.biochem.7b00627
SN  - 0006-2960
VL  - 56
SP  - 4592
EP  - 4605
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Friemel, Martin
A1  - Marelja, Zvonimir
A1  - Li, Kuanyu
A1  - Leimkühler, Silke
T1  - The N-Terminus of Iron-Sulfur Cluster Assembly Factor ISD11 Is Crucial for Subcellular Targeting and Interaction with L-Cysteine Desulfurase NFS1
JF  - Biochemistry
N2  - Assembly of iron sulfur (FeS) clusters is an important process in living cells. The initial sulfur mobilization step for FeS cluster biosynthesis is catalyzed by L-cysteine desulfurase NFS1, a reaction that is localized in mitochondria in humans. In humans, the function of NFS1 depends on the ISD11 protein, which is required to stabilize its structure. The NFS1/ISD11 complex further interacts with scaffold protein ISCU and regulator protein frataxin, thereby forming a quaternary complex for FeS cluster formation. It has been suggested that the role of ISD11 is not restricted to its role in stabilizing the structure of NFS1, because studies of single-amino acid variants of ISD11 additionally demonstrated its importance for the correct assembly of the quaternary complex. In this study, we are focusing on the N-terminal region of ISD11 to determine the role of N-terminal amino acids in the formation of the complex with NFS1 and to reveal the mitochondria) targeting sequence for subcellular localization. Our in vitro studies with the purified proteins and in vivo studies in a cellular system show that the first 10 N-terminal amino acids of ISD11 are indispensable for the activity of NFS1 and especially the conserved "LYR" motif is essential for the role of ISD11 in forming a stable and active complex with NFS1.
Y1  - 2017
U6  - https://doi.org/10.1021/acs.biochem.6b01239
SN  - 0006-2960
VL  - 56
SP  - 1797
EP  - 1808
PB  - American Chemical Society
CY  - Washington
ER  -