Concepts of Mutagenesis

The fundamental concept of the transition state stabilization was introduced to Linus Pauling in 1948 who said I think that enzymes are molecules that are complementary in structure to the activated complex of the reactions that they catalyze, that is, the molecular configuration that is intermediate between the reacting substances and the product of the reaction . This concept was widely accepted and used for the interpretation of experimental structural and kinetics data on enzyme catalysis, for the design of new substrates and inhibitors and for chemical mimicking of enzyme reactions. Decisive contributions in this area have been made by structural physical methods, X-ray analysis, in particular, and site-directed mutagenesis. 

Kirsch-Volders, M., Aardema, M., and Elhajouji, A. (2000). Concepts of threshold in mutagenesis and carcinogenesis. Mutat Res 464, 3-11. 

The concept of artificial metaUoenzymes displays attractive features for both biocatalysis and chemocatalysis precious metal reactivity, genetic optimization potential, and well-defined second coordination sphere provided by a protein scaffold. Such scaffolds are further tunable by mutagenesis and can be used as linkers for immobilization strategies. 

Most contemporary mechanistic models are based on the hypothesis that the action of various modes of DNA repair on lesions in DNA is the critical determinant of mutagenesis and survival. For our purposes, all modes of DNA repair can be regarded operationally as being either error-free (EFR) or error-prone (EPR) the relationship of these operational concepts to DNA replication or the enzyme complexes involved need not concern us here. Thus, we can write the following general mechanistic equations for the hit functions introduced in equations (4)-(6) ... 

The three-dimensional structure of the PMT active site is not known. The protein structure of a Thermotoga maritima spermidine synthase obtained by protein crystallisation (229) suggested that those amino acids of the SPDS active site that were continuously different between PMTs and SPDS were responsible for the differences in co-substrate acceptance. Mutagenesis of those two amino acids in the D. stramonium PMT with the idea of changing PMT activity into spermidine synthase, however, resulted in a complete loss of catalytic activity (88). A refined protein model of PMT constructed as a consequence of the result discouraged the concept of comparable substrate and co-substrate binding in PMT and SPDS. Rather, the substrate putrescine binds differentially at the active sites of both enzymes. 

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