The process of determining the amino-acid sequence of a protein or its component polypeptides. The technique most commonly used is Edman degradation (devised by Pehr Edman), in which the terminal amino-acid residues are removed sequentially and identified chromatographically. Each step is automated and the whole process can now be performed by a single machine – the sequenator. Large polypeptides must be cleaved into smaller peptides before sequencing.
The results of this chemical sequencing can often be compared with the amino-acid sequence deduced by DNA sequencing. The gene coding for the protein under investigation may be found by screening a DNA library, for example by Western blotting. However, the base sequence of the gene gives only the amino-acid sequence of the nascent protein, i.e. before post-translational modification. The sequence of the functional protein can only be found by chemical analysis.
Subjects: Medicine and Health — Biological Sciences.