Chorismate combinatorial

It is in the realm of very large combinatorial libraries that selection rather than screening gains crucial importance. As the focus shifts from randomizing an eight-residue peptide to a 100 amino acid protein (the typical size of a small functional domain, for example a chorismate mutase domain), the number of sequence permutations rises to an astronomical 20100. The ability to assay even a tiny fraction of this sequence space in directed molecular evolution experiments demands selection, even though initial development of an appropriate system may be considerably more involved than the setup of a screening procedure. 

In contrast to methods involving single substitutions, combinatorial strategies are ideally suited for evaluating the complex network of interactions in proteins that ultimately determine form and function [73]. As shown in the mechanistic and structural investigations of chorismate mutases, degenerate protein ensembles can illuminate subtle trends that might be missed in analyses of individual amino acid replace-... 

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