Ligated Twins

In ligated twins the mesogenic units are connected in a central position by a rigid or flexible spacers. The first examples of such compounds with a rigid spacer (18) were synthesized by Griffin et al. [217, 218]. 

The following protocol for EPL, including purification using a CBD fusion tag followed by native chemical ligation, is based on the methods of Muir et al. (1998), Chong et al. (1997, 1998), Evans et al. (1998), Severinov and Muir (1998), and the NEB instruction manual for the IMPACT-TWIN system. The recombinant protein is recovered from the affinity column as the thioester derivative ready for reaction with a N-terminal Cys peptide or another tag containing a Cys residue. 

The principle of in vivo cyclization is based on the circular permutation of precursor proteins containing an intein (Fig. 1.6 C) [74, 75, 80, 81]. A naturally occurring split intein, DnaE from Synechocystis sp. PCC6803, was first successfully used for cyclization. However, similarly to the IPL/EPL approach, a mixture of linear and circular forms is obtained, presumably because of hydrolysis of an intermediate [73, 75]. On the other hand, artificially split inteins such as Pl-Pful, DnaB, and the RecA intein have been successfully applied for in vivo cyclization, and only circular forms were observed [80-82], suggesting that the circular permutation approach is more suitable for cyclization. Compared to the IPL/EPL or the TWIN system, in vivo cyclization does not require any external thiol group for cyclization, similarly to protein ligation with split inteins. Moreover, there are no undesired products, such as linear forms or polymers, originating from intermolecular reactions. 

After having shown that combination of two catalytic modules in one molecule results in twin ribozymes with double cleavage activity we wondered whether twin ribozymes can also catalyze RNA ligation and thus be used for catalysis of RNA fragment-exchange reactions. If all fragments (substrates and cleavage products)... 

H. Dehne, A. Roger, D. Demus, S. Diele, H. Ktesse, G. Pelzl, W. Weissflog, Sulphur ligated Siamese twin mesogens. Liq. Cryst. 6, 47-62 (1989)... 

Molecules of liquid crystals can be built from a variety of structural elements. For instance, in 1927 Vorlander synthesized the first liquid crystal twins, now called tail-to-tail twins. A Siamese twin mesogen is a compound in which two independently mesogenic parts are joined in a single molecule. While earlier twins were ligated by carbon-containing groups such as methylene, Dehne et aV have shown that sulfur, sulfinyl or sulfonyl groups can perform a similar role. Anatomy of MLCs from the point of view of possible structures was reviewed in detail by Demus. ... 

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