title: Specific and efficient binding of xeroderma pigmentosum complementation group A to double-strand/single-strand DNA junctions with 3'- and/or 5'-ssDNA branches.
abstract: Human XPA is an important DNA damage recognition protein in nucleotide excision repair (NER). We previously observed that XPA binds to the DNA lesion as a homodimer [Liu, Y., Liu, Y., Yang, Z., Utzat, C., Wang, G., Basu, A. K., and Zou, Y. (2005) Biochemistry 44, 7361-7368]. Herein we report that XPA recognized undamaged DNA double-strand/single-strand (ds-ssDNA) junctions containing ssDNA branches with binding affinity (Kd = 49.1 +/- 5.1 nM) much higher than its ability to bind to DNA damage. The recognized DNA junction structures include the Y-shape junction (with both 3'- and 5'-ssDNA branches), 3'-overhang junction (with a 3'-ssDNA branch), and 5'-overhang junction (with a 5'-ssDNA branch). Using gel filtration chromatography and gel mobility shift assays, we showed that the highly efficient binding appeared to be carried out by the XPA monomer and that the binding was largely independent of RPA. Furthermore, XPA efficiently bound to six-nucleotide mismatched DNA bubble substrates with or without DNA adducts including C8 guanine adducts of AF, AAF, and AP and the T[6,4]T photoproducts. Using a set of defined DNA substrates with varying degrees of DNA bending, we also found that the XPC-HR23B complex recognized DNA bending, whereas neither XPA nor the XPA-RPA complex could bind to bent DNA. We propose that, besides DNA damage recognition, XPA may also play a novel role in stabilizing, via its high affinity to ds-ssDNA junctions, the DNA strand opening surrounding the lesion for stable formation of preincision NER intermediates. Our results provide a plausible mechanistic interpretation for the indispensable requirement of XPA for both global genome and transcription-coupled repairs. Since ds-ssDNA junctions are common intermediates in many DNA metabolic pathways, the additional potential role of XPA in cellular processes is discussed.
authors.affiliation: Department of Biochemistry and Molecular Biology, James H. Quillen College of Medicine, East Tennessee State University, Johnson City, Tennessee 37614, USA.
authors.forename: Zhengguan
authors.initials: Z
authors.lastname: Yang
authors.forename: Marina
authors.initials: M
authors.lastname: Roginskaya
authors.forename: Laureen C
authors.initials: LC
authors.lastname: Colis
authors.forename: Ashis K
authors.initials: AK
authors.lastname: Basu
authors.forename: Steven M
authors.initials: SM
authors.lastname: Shell
authors.forename: Yiyong
authors.initials: Y
authors.lastname: Liu
authors.forename: Phillip R
authors.initials: PR
authors.lastname: Musich
authors.forename: Constance M
authors.initials: CM
authors.lastname: Harris
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Harris
authors.forename: Yue
authors.initials: Y
authors.lastname: Zou
mesh_terms: D000818:Animals; D016367:Baculoviridae / Q000235:genetics; D001483:Base Sequence; D002460:Cell Line; D018736:DNA Adducts / Q000737:chemistry / Q000378:metabolism; D004249:DNA Damage; D004260:DNA Repair; D004277:DNA, Single-Stranded / Q000737:chemistry / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D011485:Protein Binding / Q000235:genetics; D018411:Spodoptera / Q000235:genetics; D051760:Xeroderma Pigmentosum Group A Protein / Q000235:genetics / Q000378:metabolism*
chemical_list: D018736:DNA Adducts; D004277:DNA, Single-Stranded; D004268:DNA-Binding Proteins; D051760:Xeroderma Pigmentosum Group A Protein; C086984:XPC protein, human