Assessment of sequence features in internal regions of proteins

Determination of amino acid replacements or assessment of sequence features localized in internal regions of natural or genetically engineered proteins can be performed in some cases with the expenditure of a minimum amount of work and protein material. The procedure requires fragmentation of a protein sample by a chemical or enzymatic method: one of the fragments should include the sequence tract under investigation, suitably preceded by one or more prolyl residues. Classical Edman degradation can be performed on the whole mixture of fragments, thus avoiding the rate-limiting step of peptide purification. Sequence data become readable after performance of reaction with o-phthalaldehyde at the level of proline residues in the relevant peptide. Two specific cases illustrate the potentiality of the procedure.