Elucidation of Protein Function by Chemical Modification

Chemical modification can be introduced at the amino-acid side chains and/or the N/C-terminus of a protein. In this chapter, we show a few examples of chemical protein modification methods and application of these methods to solve biological questions. 

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Group-specific chemical modification remains a useful method for studies of structure-function relationships in protein molecules, although unambiguous identification of essential amino acid residues and elucidation of their function are nowadays accomplished mainly by X-ray crystallography and site-directed mutagenesis. Chemical modifications... 

Development of methods for control of surface activity by means of chemical and physicochemical modifications of the protein molecules. These modifications may help to elucidate the basis of protein functionality and should enable the design of better protein derivatives with the needed properties. 

In our laboratory we first isolated the major lethal protein (termed Cobrotoxin) of non-enzymatic nature from the venom of Taiwan cobra Naja naja atra) in 1964 and subsequently purified and crystallized the protein. The primary structure and the disulfide linkages with various efforts by chemical modification and immunological methods in elucidation of the structure-function relationship of this important venom neurotoxin have since been accomplished. Structure-activity correlations have been drawn from chemical modification carried out on both pre- and post-synaptic neurotoxins. With recent advances in DNA recombination and protein engineering, we feel that the time is now ripe to apply these techniques to the isolation and characterization of the genes encoding these toxins. Detailed structural and site-specific mutational studies on the cDNA clones of neurotoxins of both types may complement our previous chemical modifications of the functional role of some amino acid residues in neurotoxins and lead to insight into the modes of action for these biologically active molecules. 

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