Protein Sequencing

It is approaching half a century since Edman developed a chemistry for the determination of the N-terminus of a protein or peptide (1 ), and thts chemistry is still being used today. in the intervening decades various ancillary techniques have come (and some have gone) that have allowed the field to develop. Apart from the automation of Edman chemistry itself, the most sigmticant advances have been improvements in sample preparation and the advent of mass spectrometric techniques. in the early days the task of sequencing a protem was a signnificant one, limited to those protems that could be prepared in sufficiently large amounts. Then, the aim (other than to develop the technology) was to obtam the full sequence of the protein in question to begin to understand how protems were structured, which was done by use of Edman chemistry exclusively. Currently, the situation is different, and it is usually necessary to obtam only partial protein sequence from the protein itself From the partial sequence, suitable ohgonucleotides can be designed and used to clone the corresponding gene, which can be rapidly analyzed to yield the full sequence, For identification of a protein the partial sequence may need to be only 3–5 residues long Such short sequences, known as “sequence tags,” are currently of importance in the study of the “proteome,” the set of protems that is expressed by the genome. Studies of the proteome follow the results of genome sequencing, which are giving an explosion of information. The sequence of the genome suggests what proteins might be made, but does not prove which are actually expressed in any gtven tissue(s), how they are regulated, or what their functions e For these purposes there is a need to separate and identify mdividual proteins, then to correlate then presence and modification with function.