What is the method for determining protein sequences?
Protein sequences, also known as amino acid sequences, refer to the linear order of amino acids in a protein. This sequence determines the three-dimensional structure and function of the protein. There are mainly two methods for determining protein sequences: Edman degradation and mass spectrometry.
1. Edman Degradation
The Edman degradation method was invented by Pehr Edman in the 1950s. This method involves repetitive chemical steps to sequentially remove the N-terminal amino acid of a protein, followed by chromatography to identify each type of amino acid. Although this method is very accurate, it is cumbersome and can only determine protein sequences less than 50 amino acids in length.
2. Mass Spectrometry
Mass spectrometry is currently the most commonly used method for determining protein sequences. It uses the movement properties of proteins in electric and magnetic fields to measure their mass and charge. First, the protein needs to be fragmented into shorter pieces, then ionized into ions, and finally analyzed using a mass spectrometer. The advantages of mass spectrometry are its speed, high sensitivity, and ability to sequence long sequences. Especially when combined with liquid chromatography and tandem mass spectrometry, it can analyze thousands of proteins simultaneously, making it suitable for proteomics research.
3. Examples
There are many successful examples of protein sequence determination. For instance, by determining the protein sequence of insulin, scientists discovered that it consists of two polypeptide chains linked by disulfide bonds, and this structure is crucial for its function. Another example is determining the protein sequence of immunoglobulins, which helped scientists understand the diversity and specificity of antibodies.
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