zinostatin and kedarcidin-chromophore

Enediyne chromoproteins are potent antitumor antibiotic agents. They consist of a labile nine-membered enediyne chromophore non-covalently associated with a stabilizing acidic polypeptide. Studies in vitro on three members of this superfamily of natural products--kedarcidin, maduropeptin and neocarzinostatin--demonstrated that their chromophores cleave DNA at sites specific to each chromophore. Recently, we showed that these chromoproteins possess proteolytic activity against histones in vitro, with histone H1 as a preferred substrate. Based on these results, we speculated that this selective proteolytic activity may be important in vivo in the delivery of the enediynes intact to the DNA in chromatin.. We show here that each chromoprotein generates a unique set of H1 fragments as revealed by gel analyses of the H1 cleavage reaction products. To probe the observed cleavage specificity, we synthesized a 24-amino-acid peptide representing a basic region of histone H1. This model peptide was incubated individually with similar concentrations of the kedarcidin, neocarzinostatin and maduropeptin chromoproteins as well as the kedarcidin apoprotein. The reaction products were analyzed by electrospray liquid chromatography/mass spectrometry. Our results indicate that all proteins cleave the peptide at selected backbone amides, and that these sites vary according to the chromoprotein used. Moreover, the kedarcidin apoprotein appears to be less specific than the kedarcidin chromoprotein complex.. The small size, unique architecture and very acidic nature of the enediyne chromoproteins are highly unusual. These natural products exhibit the dual functionalities of specific DNA cleavage and selective proteolytic activity. This observation adds to the fascinating properties of these molecules and suggests that it is possible not only to design small moieties to cleave DNA but also to conceive of small proteins to deliver these moieties intact to defined areas of chromatin.

Topics: Alkynes; Amino Acid Sequence; Anti-Bacterial Agents; Antibiotics, Antineoplastic; Apoproteins; Chromatin; Chromatography, High Pressure Liquid; Cycloparaffins; DNA; Endopeptidases; Enediynes; Histones; Intercellular Signaling Peptides and Proteins; Mass Spectrometry; Molecular Sequence Data; Naphthalenes; Peptides; Zinostatin

Kedarcidin chromophore is a 9-membered enediyne, recently isolated from an actinomycete strain. In vivo studies show this molecule to be extremely active against P388 leukemia and B16 melanoma. Cytotoxicity assays on the HCT116 colon carcinoma cell line result in an IC50 value of 1 nM. In vitro experiments with phi X174, pM2 DNA, and 32P-end-labeled restriction fragments demonstrate that this chromophore binds and cleaves duplex DNA with a remarkable sequence selectivity producing single-strand breaks. The cleavage chemistry requires reducing agents and oxygen similar to the other naturally occurring enediynes. Certain cations (Ca2+ and Mg2+) prevent strand cleavage. High-resolution 1H NMR studies on the chromophore in the presence of calcium chloride implicate the 2-hydroxynaphthoyl moiety in DNA binding. Interestingly, the kedarcidin chromophore appears structurally related to neocarzinostatin yet recognizes specific DNA sequences in a manner similar to calicheamicin gamma 1I, an enediyne with a significantly different structure. Moreover, kedarcidin and calicheamicin share a DNA preferred site, the TCCTN-mer. These observations indicate that the individual structural features of these agents are not solely responsible for their DNA selectivity. Rather, a complementarity between their overall tertiary structure and the local conformation of the DNA at the binding sites must play a significant role in the recognition process.

Topics: Alkynes; Bacteriophage phi X 174; Base Sequence; Catalase; Cycloparaffins; DNA Damage; DNA, Circular; DNA, Single-Stranded; DNA, Viral; Enediynes; Indicators and Reagents; Magnetic Resonance Spectroscopy; Molecular Sequence Data; Molecular Structure; Naphthalenes; Oligodeoxyribonucleotides; Proteins; Restriction Mapping; Superoxide Dismutase; Zinostatin