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The Skaggs Institute For Chemical Biology
Scientific Report 1997-1998


Bioorganic Chemistry of Proteins


P.E. Dawson, G. Beligere, A. Brik, T. Doundoulakis, T.M. Hackeng

Synthetic Protein Chemistry

Our laboratory focuses on the bioorganic chemistry of proteins. Proteins are large organic molecules of amazing compositional and conformational diversity. It is through proteins that the information stored in the DNA sequence of the genome is given functional form; consequently, all cellular processes are mediated through the actions of proteins. Efforts to understand the molecular basis for protein function have largely used biological techniques to modify the sequence of amino acids that defines a protein's structure and function. Unfortunately, these modifications are limited to the naturally occurring 20 amino acids.

We have developed a chemical approach for producing the large polypeptide chains that make up protein molecules. Synthetic access to these polypeptides enables us to change the structure of a protein in ways impossible in Nature.

We use solid-phase peptide synthesis to generate peptides up to approximately 50 amino acids long and then use chemoselective reactions to assemble the peptides into proteins up to about 200 amino acids long. This chemical ligation approach greatly facilitates the synthesis of proteins of moderate size and has opened up the world of proteins to the synthetic tools of organic chemistry (Fig. 1). In the past year, we further developed the native chemical ligation technique by increasing the number of ligation sites that can be used and by facilitating the synthesis of the functionalized polypeptide intermediates.

Backbone Interactions In Protein Stability and Folding

We are using our ability to chemically manipulate proteins to probe some fundamental issues in protein science. One of the greatest challenges in the biochemical sciences is to understand the forces and mechanisms that guide a linear polypeptide into its functional folded form. We are investigating the role of the polypeptide backbone in these processes. Although it accounts for about 50% of the mass of a protein, the backbone of proteins cannot be modified by standard biological methods. In our studies, we are replacing the natural amide bond in the polypeptide backbone with an ester bond (Fig. 2).

In particular, we selected 2 protein domains, the coiled coil from the transcription factor GCN4 and a protein-based serine protease inhibitor, CI2. Both of these proteins have a prominent α-helix that is an essential component of their 3-dimensional structure. Systematic incorporation of ester bonds into these well-studied proteins will give new insight into the role of backbone hydrogen-bonding interactions in the formation and stability of α-helical structures in proteins.

Publications

Dawson, P.E., Churchill, M.J., Ghadiri, M.R., Kent, S.B.H. Modulation of reactivity in native chemical ligation through the use of thiol additives. J. Am. Chem. Soc. 119:4325, 1997.

Dawson, P.E., Fitzgerald, M.C., Muir, T.W., Kent, S.B.H. Methods for the chemical synthesis and readout of self-encoded arrays of polypeptide analogues. J. Am. Chem. Soc. 119:7917, 1997.

Hackeng, T.M., Mounier, C.M., Bon, C., Dawson, P.E., Griffin, J.H., Kent, S.B.H. Total chemical synthesis of enzymatically active human type-II secretory phospholipase A(2). Proc. Natl. Acad. Sci. U.S.A. 94:7845, 1997.

 

 







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