title: DNA-induced alpha-helix capping in conserved linker sequences is a determinant of binding affinity in Cys(2)-His(2) zinc fingers.
abstract: High-affinity, sequence-specific DNA binding by Cys(2)-His(2) zinc finger proteins is mediated by both specific protein-base interactions and non-specific contacts between charged side-chains and the phosphate backbone. In addition, in DNA complexes of multiple zinc fingers, protein-protein interactions between the finger units contribute to the binding affinity. We present NMR evidence for another contribution to high- affinity binding, a highly specific DNA-induced helix capping involving residues in the linker sequence between fingers. Capping at the C terminus of the alpha-helix in each zinc finger, incorporating a consensus TGEKP linker sequence that follows each finger, provides substantial binding energy to the DNA complexes of zinc fingers 1-3 of TFIIIA (zf1-3) and the four zinc fingers of the Wilms' tumor suppressor protein (wt1-4). The same alpha-helix C-capping motif is observed in the X-ray structures of four other protein-DNA complexes. The structures of each of the TGEKP linkers in these complexes can be superimposed on the linker sequences in the zf1-3 complex, revealing a remarkable similarity in both backbone and side-chain conformations. The canonical linker structures from the zinc-finger-DNA complexes have been compared to the NMR structure of the TGEKP linker connecting fingers 1 and 2 in zf1-3 in the absence of DNA. This comparison reveals that additional stabilization likely arises in the DNA complexes from hydrogen bonding between the backbone amide of E3 and the side-chain O(gamma) of T1 in the linker. We suggest that these DNA-induced C-capping interactions provide a means whereby the multiple-finger complex, which must necessarily be domain-flexible in the unbound state as it searches for the correct DNA sequence, can be "snap-locked" in place once the correct DNA sequence is encountered. These observations provide a rationale for the high conservation of the TGEKP linker sequences in Cys(2)-His(2) zinc finger proteins.
authors.affiliation: Department of Molecular Biology, Skaggs Institute for Chemical Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA, 92037, USA.
authors.forename: J H
authors.initials: JH
authors.lastname: Laity
authors.forename: H J
authors.initials: HJ
authors.lastname: Dyson
authors.forename: P E
authors.initials: PE
authors.lastname: Wright
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D017124:Conserved Sequence; D018360:Crystallography, X-Ray; D003545:Cysteine; D004247:DNA / Q000737:chemistry / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000378:metabolism; D006639:Histidine; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods; D017433:Protein Structure, Secondary; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D035582:Transcription Factor TFIIIA; D014157:Transcription Factors / Q000737:chemistry; D025721:WT1 Proteins; D016335:Zinc Fingers
chemical_list: D004268:DNA-Binding Proteins; D035582:Transcription Factor TFIIIA; D014157:Transcription Factors; D025721:WT1 Proteins; D006639:Histidine; D004247:DNA; D003545:Cysteine