Re-ligation

Camptothecin acts by forming a reversible ternary complex ( cleavable complex ) with DNA and topoisomerase I, preventing the re-ligation of the DNA strand cut by topoisomerase to allow relaxation, and thus inducing apoptosis [14]. The X-ray structure of crystals of such a complex of a 22-base DNA fragment with topoisomerase I and topotecan has been reported [15], and molecular models of the interaction have been proposed [16-18]. This kind of information should be of help in... 

The most thoroughly studied mechanism of protein protease inhibitors is that of the standard mechanism (or Canonical or Laskowski mechanism) inhibitors of serine proteases (1) (Fig. 2). Standard mechanism inhibitors include the Kazal, Kunitz, and Bowman-Birk family of inhibitors and bind in a lock-and-key fashion. Ah standard mechanism inhibitors insert a reactive loop into the active site of the protease, which is complementary to the substrate specificity of the target protease and binds in an extended fi-sheet with the enzyme in a substrate-like manner. WhUe bound to the protease, the scissile bond of standard mechaiusm inhibitors is hydrolyzed very slowly, but products are not released and the amide bond is re-ligated. The standard mechanism is an efficient way to inhibit serine proteases, and it is thus used by many structurally... 

The other major repair pathway involved in DNA DSB repair is NHEJ. While this pathway brings about DSB repair, it is also involved in immunological diversification by re-ligating the products of recombinase (RAGl and RAG2) cleavage. Unlike... 

Hin DNA invertase has been sequenced and X-ray studies have been performed on the protein on its complexes with DNA. It consists of a 52-residue C-terminal DNA-binding domain and a 138-bp catalytic domain. yS-Resolvase (a dimer of identical 120-resi-due subunits encoded by the y5 transposon) displays 40 % sequence identity with the Hin catalytic domain, and catalyses a similar reaction, i.e. a 2-bp staggered cleavage, exchange, and re-ligation of duplex DNA. Whereas Hin catalyses an inversion, y8 resolvase catalyses a site-specific deletion. 

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