Rhodium intercalators as novel peptide delivery systems to the major groove of DNA : towards the design of artificial repressors

Citation

Sardesai, Niranjan Y. (1995) Rhodium intercalators as novel peptide delivery systems to the major groove of DNA : towards the design of artificial repressors. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/0v7r-fp28. https://resolver.caltech.edu/CaltechETD:etd-10222007-132632

Abstract

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Phenanthrenequinone diimine (phi) complexes of rhodium(III) bearing tethered peptides have been designed to serve as metallointercalating anchors to deliver peptide side chain functionalities for DNA recognition in the major groove. Metal-peptide complexes containing 11-15 amino acid residues were prepared using two complementary synthetic strategies: by direct coupling of a pendant carboxylate on the coordinatively saturated rhodium complex, [...] (phen'=5-amidoglutaryl-1, 10-phenanthroline), to the N-terminus of a resin-bound peptide in a manner analogous to the chain-elongation step in solid phase peptide synthesis; or by coupling phen' containing the pendant carboxylate to the resin-bound peptide, followed by coordination of [...] to the bidentate chelator attached to the peptide. With coordination complexes which are stable to peptide deprotection and cleavage conditions from the resin, the solid phase synthetic strategies prove convenient to apply. The metal-peptide complexes have been characterized by amino acid analysis, electronic spectroscopy, circular dichroism and mass spectrometry, where a novel pattern of peptide fragmentation facilitates the detailed sequence analysis of the appended peptide. All the metal-peptide complexes bind and, with photoactivation, cleave DNA with evidence of major groove chemistry. Significantly, the DNA site-specificity is seen to depend on the peptide side-chain functional groups. In one series, a single glutamate at position 10 is found to be essential in directing DNA site-recognition to the sequence 5'-CCA-3'. Methylation of the glutamate side chain or single ElOQ, E1OD, E1OA mutations abolish this selectivity. The glutamate is essential to maintain [...]-helicity in the peptide and make base specific contacts, thereby providing a glutamate switch for site-specific DNA recognition. A second series, based on the recognition helix of the phage 434 repressor, reproduces operator binding. Photocleavage and MPE-Fe footprint analysis indicates that these metal-peptide complexes bind to the 5'-ACAA-3' operator sequences as monomers at 10 nM concentration and differentiate between operator site variants. These studies represent a new strategy to create an array of metal-peptide complexes with differing sequence specificity for DNA and suggest a route to the construction of small molecules that function as artificial repressors.

Thesis Files