title: Structural and functional analyses of five conserved positively charged residues in the L1 and N-terminal DNA binding motifs of archaeal RADA protein.
abstract: RecA family proteins engage in an ATP-dependent DNA strand exchange reaction that includes a ssDNA nucleoprotein helical filament and a homologous dsDNA sequence. In spite of more than 20 years of efforts, the molecular mechanism of homology pairing and strand exchange is still not fully understood. Here we report a crystal structure of Sulfolobus solfataricus RadA overwound right-handed filament with three monomers per helical pitch. This structure reveals conformational details of the first ssDNA binding disordered loop (denoted L1 motif) and the dsDNA binding N-terminal domain (NTD). L1 and NTD together form an outwardly open palm structure on the outer surface of the helical filament. Inside this palm structure, five conserved basic amino acid residues (K27, K60, R117, R223 and R229) surround a 25 A pocket that is wide enough to accommodate anionic ssDNA, dsDNA or both. Biochemical analyses demonstrate that these five positively charged residues are essential for DNA binding and for RadA-catalyzed D-loop formation. We suggest that the overwound right-handed RadA filament represents a functional conformation in the homology search and pairing reaction. A new structural model is proposed for the homologous interactions between a RadA-ssDNA nucleoprotein filament and its dsDNA target.
authors.affiliation: Institute of Biochemical Sciences, National Taiwan University, Taipei, Taiwan.
authors.forename: Li-Tzu
authors.initials: LT
authors.lastname: Chen
authors.forename: Tzu-Ping
authors.initials: TP
authors.lastname: Ko
authors.forename: Yu-Wei
authors.initials: YW
authors.lastname: Chang
authors.forename: Kuei-An
authors.initials: KA
authors.lastname: Lin
authors.forename: Andrew H-J
authors.initials: AH
authors.lastname: Wang
authors.forename: Ting-Fang
authors.initials: TF
authors.lastname: Wang
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D019843:Archaeal Proteins / Q000737:chemistry* / Q000378:metabolism / Q000502:physiology*; D017124:Conserved Sequence; D019641:DNA, Archaeal / Q000378:metabolism*; D004277:DNA, Single-Stranded / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000378:metabolism / Q000502:physiology*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017386:Sequence Homology, Amino Acid; D048229:Sulfolobus solfataricus / Q000737:chemistry*
chemical_list: D019843:Archaeal Proteins; D019641:DNA, Archaeal; D004277:DNA, Single-Stranded; D004268:DNA-Binding Proteins; C117252:RadA protein, archaeal