Why Does Protein Sequencing Start at the N-Terminus?

Degradation in protein sequencing usually starts from the N-terminus (amino terminal) mainly due to:

 

1. Enzyme Specificity

The enzyme used for protein sequencing, such as phenyl isothiocyanate (PITC) in Edman degradation, specifically reacts with the N-terminal amino acid of the protein. This specificity ensures the accuracy and repeatability of the sequencing process.

 

2. Convenience of Sequencing

Starting from the N-terminus, each amino acid can be removed step by step and identified. This method is relatively direct and efficient, as the amino acid sequence of proteins is synthesized from the N-terminus to the C-terminus.

 

3. Biological Significance

In some cases, the N-terminus of the protein may have special biological significance, such as the presence of signal peptides, which are of interest to researchers.

 

However, there are also protein sequencing methods that start from the C-terminus, such as the use of carboxypeptidase C, but these methods are generally not as common or efficient as those that start from the N-terminus. With the development of mass spectrometry technology, protein mass spectrometry analysis provides an alternative, highly flexible protein sequencing method, which can identify the entire or partial amino acid sequence of a protein, whether from the N-terminus or the C-terminus.