DNA recognition by metallotripeptides of the form nickel(II).Xaa-Xaa-His: Binding selectivity and mechanism of strand scission

Qi Liang, Purdue University

Abstract

DNA cleavage by synthetic tripeptides of the form NH 2-Xaa-Xaa-His-CONH2 was investigated in the presence of Ni(II) and oxygen activating agents. The metallotripeptides Ni(II)•Gly-Gly-His, Ni(II)•Lys-Gly-His, and Ni(II)•Arg-Gly-His were found to induce strand scission via a non-diffusible, non-base specific oxidant in the minor groove. The positively charged metallopeptides Ni(II)•Lys-Gly-His and Ni(II)•Arg-Gly-His have a high tendency to cleave DNA at mixed A/T-rich regions. Substitution of D-His for L-His in the tripeptide is believed to alter the site-selectivity observed due to structural differences of the two metal complex isomers. The site-selectivity of the metallopeptides may be due to the formation of a direct molecular interaction or steric complementarity, which is facilitated by electrostatic interactions. Analysis of cleaved DNA fragments at single nucleotide resolution points to a mechanism similar to Fe(II)•bleomycin induced DNA cleavage, initiated from the abstraction of a C4′-H and resulting in the release of 3′- and 5′-phosphate fragments, 3′-phosphoglycolates, 3′-alkaline-labile fragments, and monomeric products (nucleobases and nucleobase propenals). The reaction pathways were sensitive to the structure of the metallopeptides. However, the site-selectivity and reaction pathways of DNA cleavage induced by Ni(II)•Lys-Gly-His were not affected by the activating agent (oxone, MMPP, and H2O2) employed nor common radical scavengers (ethanol, t-butyl alcohol, DMSO, and mannitol). These observations indicate that the active intermediate generated from activation of these metallotripeptides is most likely a ligand-bound Ni(III)-O•− or Ni(IV)=O species. These studies demonstrate that this relatively simple tripeptide series is sensitive to DNA structure and is capable of interacting site-selectively, suggesting the possibility of exploiting the chemical diversity and chirality of peptides in the further design of DNA binding and modifying agents.

Degree

Ph.D.

Advisors

Long, Purdue University.

Subject Area

Biochemistry

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