title: The Association of the Xeroderma Pigmentosum Group D DNA Helicase (XPD) with Transcription Factor IIH Is Regulated by the Cytosolic Iron-Sulfur Cluster Assembly Pathway.
abstract: Xeroderma pigmentosum group D (XPD) helicase is a component of the transcription factor IIH (TFIIH) transcription complex and plays essential roles in transcription and nucleotide excision repair. Although iron-sulfur (Fe-S) cluster binding by XPD is required for activity, the process mediating Fe-S cluster assembly remains poorly understood. We recently identified a cytoplasmic Fe-S cluster assembly (CIA) targeting complex composed of MMS19, CIAO1, and FAM96B that is required for the biogenesis of extramitochondrial Fe-S proteins including XPD. Here, we use XPD as a prototypical Fe-S protein to further characterize how Fe-S assembly is facilitated by the CIA targeting complex. Multiple lines of evidence indicate that this process occurs in a stepwise fashion in which XPD acquires a Fe-S cluster from the CIA targeting complex before assembling into TFIIH. First, XPD was found to associate in a mutually exclusive fashion with either TFIIH or the CIA targeting complex. Second, disrupting Fe-S cluster assembly on XPD by either 1) depleting cellular iron levels or 2) utilizing XPD mutants defective in either Fe-S cluster or CIA targeting complex binding blocks Fe-S cluster assembly and prevents XPD incorporation into TFIIH. Finally, subcellular fractionation studies indicate that the association of XPD with the CIA targeting complex occurs in the cytoplasm, whereas its association with TFIIH occurs largely in the nucleus where TFIIH functions. Together, these data establish a sequential assembly process for Fe-S assembly on XPD and highlight the existence of quality control mechanisms that prevent the incorporation of immature apoproteins into their cellular complexes.
authors.affiliation: From the Department of Biological Chemistry, David Geffen School of Medicine, University of California, Los Angeles, California 90095.
authors.forename: Ajay A
authors.initials: AA
authors.lastname: Vashisht
authors.affiliation: From the Department of Biological Chemistry, David Geffen School of Medicine, University of California, Los Angeles, California 90095.
authors.forename: Clarissa C
authors.initials: CC
authors.lastname: Yu
authors.affiliation: From the Department of Biological Chemistry, David Geffen School of Medicine, University of California, Los Angeles, California 90095.
authors.forename: Tanu
authors.initials: T
authors.lastname: Sharma
authors.affiliation: From the Department of Biological Chemistry, David Geffen School of Medicine, University of California, Los Angeles, California 90095.
authors.forename: Kevin
authors.initials: K
authors.lastname: Ro
authors.affiliation: From the Department of Biological Chemistry, David Geffen School of Medicine, University of California, Los Angeles, California 90095 jwohl@mednet.ucla.edu.
authors.forename: James A
authors.initials: JA
authors.lastname: Wohlschlegel
mesh_terms: D001665:Binding Sites; D002467:Cell Nucleus / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D004247:DNA / Q000737:chemistry; D004265:DNA Helicases / Q000378:metabolism; D004260:DNA Repair; D006367:HeLa Cells; D006801:Humans; D007501:Iron / Q000737:chemistry; D007506:Iron-Sulfur Proteins / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism; D011485:Protein Binding; D040901:Proteomics; D013347:Subcellular Fractions / Q000378:metabolism; D013455:Sulfur / Q000737:chemistry; D051758:Transcription Factor TFIIH / Q000378:metabolism*; D051759:Xeroderma Pigmentosum Group D Protein / Q000378:metabolism*
chemical_list: D007506:Iron-Sulfur Proteins; D051758:Transcription Factor TFIIH; D013455:Sulfur; D004247:DNA; D007501:Iron; D004265:DNA Helicases; D051759:Xeroderma Pigmentosum Group D Protein; C497292:ERCC2 protein, human
keywords: DNA helicase; DNA repair; iron metabolism; iron-sulfur protein; proteomics