Development and demonstration of a trinucleotide exchange method for the directed evolution of proteins

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Every living thing contains thousands of different proteins that carry out most of the crucial jobs needed to maintain life. Proteins are synthesised as a linear sequence of amino acids, which then fold to form their functional 3D structures. All the information required for a protein to reach its functional shape is encoded in the linear sequence of amino acids, which in turn is encoded by the DNA sequence of the gene for that protein. The process of evolution involves changes to the amino acid sequence of a protein through changes to the gene. As a consequence, these changes can alter the properties of the protein and may translate into beneficial effects, allowing the organism to survive a particular environmental challenge. How changes to the amino acid sequence of a protein translate into changes in the properties of a protein is one of the most fundamental questions in biology. The advent of genetic engineering has enabled us to change the DNA sequence of genes at will and so change the nature of the linear sequence of amino acids in the protein. This has allowed us to understand how certain amino acids contribute towards the properties of a protein. It has also allowed us to modify the characteristics of proteins for use in unnatural environments such as for industrial applications. The 3D structure of a protein is highly complex and our understanding of it is still limited. Therefore our ability to predict how a particular designed mutation will affect the properties of the protein is also limited. Nature takes a different, less rational approach, by introducing mutations at random and selecting only those mutations that are of benefit. As nature has already been very successful in adapting proteins for a multitude of functions, the proposed research aims to copy the process of evolution in the laboratory by developing a method that can introduce mutations randomly into a gene in order to change the properties of a protein. We will attempt to modify the characteristics of a protein called TEM-1 beta-lactamase, one of the proteins responsible for resistance to antibiotics such as penicillin. The advent of bacterial resistance to the traditional antibiotics led to the development of new and improved penicillin-like antibiotics. Nature was quick to respond and variants of TEM-1 soon evolved to overcome the toxic effects of these new antibiotics. Using our new method, the project will investigate how and which mutations contribute to adapting TEM-1 to detoxify these new antibiotics, helping us to understand the natural process by which this occurs.