Protein semi-synthesis: new proteins for functional and structural studies

Our ability to alter and control the structure and function of biomolecules, and of proteins in particular, will be of utmost importance in order to understand their respective biological roles in complex systems such as living organisms. This challenge has prompted the development of powerful modern techniques in the fields of molecular biology, physical biochemistry and chemical biology. These fields complement each other and their successful combination has provided unique insights into protein structure and function at the level of isolated molecules, cells and organisms. Chemistry is without doubt most suited for introducing subtle changes into biomolecules down to the atomic level, but often struggles when it comes to large targets, such as proteins. In this review, we attempt to give an overview of modern and broadly applicable techniques that permit chemical synthesis to be applied to complex protein targets in order to gain control over their structure and function. As will be demonstrated, these approaches offer unique possibilities in our efforts to understand the molecular basis of protein functioning in vitro and in vivo. We will discuss modern synthetic reactions that can be applied to proteins and give examples of recent highlights. Another focus of this review will be the application of inteins as versatile protein engineering tools.