Double-chain reversal loops

Figure 2 Schematic and representative structures of different loops in G-quadruplexes (a) edgewise loop, (b) diagonal loop, (c) double-chain-reversal loop, and (d) V-shaped loop...

The four-repeat Tetrahymena telomeric d(T2G4)4 sequence was shown to form an intramolecular G-quadruplex (Figure 11a) with one double-chain-reversal and two edgewise loops. This is the first observation of a double-chain-reversal loop sequence T2 bridges three G-tetrad layers. Furthermore this... 

R. Jones and D.J. Patel, A double chain reversal loop and two diagonal loops define the architecture of a unimolecular DNA quadruplex containing a pair of stacked G syn).G syn).G anti).G anti) tetrads flanked by a... 

This concept of reversible chemical crosslinking of the chains to drastically decrease the enthalpic penalty of the folding process and to exploit the highly favored disulfide loop formation in the A-chain with m = 4, has been further developed into artificial peptide linker chains that can be excised selectively by enzymatic processing, to allow for bioexpression of the artificial proinsulins on an industrial scale. 95,96 However, to apply this approach rationally to other double-stranded cystine peptides, knowledge about their three-dimensional structure is essential. 

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