Mutational approaches site-directed mutagenesis

The carbon-carbon forming ability of aldolases has been limited in part by their narrow substrate utilization. Site-directed mutagenesis of various enzymes to alter their specificity has most often not produced the desired effect. Directed evolution approaches have furnished novel activities through multiple mutations of residues involved in recognition in no instance has a key catalytic residue been altered while activity is retained. Random mutagenesis resulted in a double mutant of E. coli 2-keto-3-deoxy-6-phosphogluconate (KDPG) aldolase with reduced but measurable enzyme activity and a synthetically useful substrate profile (Wymer, 2001). 

A cassette-replacement approach was used to facilitate the introduction of amino acid mutations at various sites of the thrombin receptor. First, unique endonuclease restriction enzyme sites were generated at several positions within the thrombin receptor cDNA by mutating the nucleotide sequences. Second, the polymerase chain reaction (PCR) with primers encoding for the desired mutations was used to generate the cDNA cassette with the appropriate endonuclease restriction enzyme sites for replacement of the wild-type sequence. The locations for the introduction of the sites were chosen based on two requirements. They needed to be at or near regions of the cDNA sequence that codes for amino acids at junctions of transmembrane domains and extracellular loops. Also, introduction of the sites did not alter the amino acid sequence of the protein. The site-directed mutagenesis method of Kunkel et al.28 was used to introduce the mutations required for generating the... 

The quest to determine whether P-gp contains multiple drug binding sites employed a number of distinct approaches. For example, site-directed mutagenesis revealed a multitude of residues that when mutated could alter the pattern of drug resistance conferred by P-gp [183-185]. The effects of mutations on the activity were... 

Scheme 19.8 Classical ligand exploration versus site-directed mutagenesis (SDM) exploration of structure-activity relationships (SAR). In the classical approach, various ligands are presented to the same receptor or active site of interest. In SDM, one or more ligands of merit are held constant and used as standards whereas various mutated forms of the receptor or active site are presented for interaction. Both approaches can produce useful SAR data and when used simultaneously, they can be highly complimentary.

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