Key-lock, template and hand-glove synthon interactions

7 KEY-LOCK , TEMPLATE AND HAND-GLOVE SYNTHON INTERACTIONS 

If such rigid molecules A and B match each other, this corresponds to the keylock type of molecular recognition. Tb match, the interacting molecules sometimes have only to orient properly in space when approaching one another and then dock (the AT or GC pairs may serve as an example). The key-lock concept of Fischer from 100 years ago (concerning enzyme-substrate interaction) is considered as 

Still another variation of this interaction comes into play, when during the approach, a new type of i nthon appears, and the q nthons match afterwards. For sample in the Hodges superhelical structure (Fig. 13.16), only after formation of the a-helices does it turn out that the leucine and valine side chains of one helix match perfectly similar synthons of the second helix ( leudne-valine zipper ). 

Nature has done it routinely for millions of years. Endonuclease (EcoRV) represents an enzyme whose function is selective chemical bond breaking between nucleotides (linking the adenine and thymine) in a single DNA strand. Fig. 13.19 shows a model of the complex of EcorV with a fragment of DNA altogether about 62000 atoms. Fig. 13.19 highlights some aspects of the interaction. 

Another masterpiece of nature - self-organization of the tobacco virus is shown in Fig. 13.20. Such a complex system self-assembles, because its parts not only fit one another ( nthons), but also found themselves in solution and made perfect matching accompanied by an energy gain. Even more spectacular is the structure and functioning of bacteriophage T (Fig. 13.21). 

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