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Advances in Protein Sequencing for Proteomics: From Edman Degradation to Mass Spectrometry
Protein sequencing is a method used to study and reveal how amino acids interact with other chains or other amino acids of the same chain.
All living organisms are made up of tiny molecules, and among these molecules, proteins are the building blocks of life because they are essential for growth and development. Proteins are long chains of amino acids that are linked by peptide bonds to form a 3-D structure. The folding of a protein helps it to get activated because folding creates pockets called active sites where the substrate usually binds, which is lacking in a linear chain of amino acids.
Protein sequencing is a chemical analysis that studies the folding of amino acids to form the 3-D structure of a protein. This is an essential part of drug discovery and healthcare research because the way a protein is folded determines its biological function and chemical properties, and allows researchers or scientists to predict diseases or any deformities.
Scientists have been using so many different ways to sequence proteins, but it used to be slow and tedious. However, over time, the sequencing of proteins has changed a lot. What started as a slow chemical method has now evolved into powerful techniques that use machines and computers.
These advances in techniques created the field of Proteomics, which is the study of all proteins in a cell or organism.
In this article, we will discuss the techniques used in protein sequencing in Proteomics, from the ancient Edman Degradation method that suits the short sequences of amino acids to advanced techniques, like mass spectrometry, and nanopore sequencing.
What are the Protein Sequencing Methods?
- The Beginning: Edman Degradation
Edman Degradation is the oldest chemical method of protein sequencing. Which was Swedish biochemist Pehr Victor Edman in 1950
How it’s done: In this method, a phenyl isothiocyanate (PITC) reagent is used to remove the N-terminal of the amino acid, one by one, sequentially. This reagent identifies one residue (typically up to 50-70 residues) at a time without harming the peptide bonds of the amino acid and couples with the amine group (N-terminal) of the amino acid, forming a phenylthiocarbamyl (PTC) derivative. This derivative is cleaved under acidic conditions and forms a phenylthiohydantoin (PTH)-amino acid, which is more stable than the PTC derivative and is analyzed by reverse-phase HPLC.
Advantages: this method is highly accurate only for short peptides; foundational technique in protein sequencing.
Limitations: It is a slow, tedious, low-throughput process, and is inefficient for large proteins or those with blocked N-terminal.
3. Peptide Mapping / Protein Digestion
This method was discovered in the 1970s-1980s. It is a method of protein mapping which does not have a single discoverer, as it kept evolving from advances in enzymatic digestion and techniques like Chromatography.
How is it done?
The 1st step of protein mapping is to cleave the protein into small fragments using an enzyme, for example, trypsin. This enzyme would cut the protein at the predictable sites, giving results in the desired amino acids like lysine and arginine, etc. These peptides are then separated by an advanced chromatography technique called HPLC or capillary electrophoresis. Each of the fragments can be further characterized by using Mass spectroscopy or any other advanced technology. After analyzing all the fragments of the protein, the overall protein sequencing or structure is mapped.
Advantages: It works best for the large proteins that are difficult to sequence directly, can detect post-translational modifications, and is highly specific, especially when combined with Mass spectroscopy. like phosphorylation or glycosylation.
Limitations: It requires the protein to be pure because a mixture of proteins can complicate the methods. It can generate only fragmented maps, and reconstructing the map without a complementary method is difficult. Protease cleavage sites must be known and accessible; blocked or modified sites can prevent digestion.
4. Mass Spectroscope
It is the main modern method for protein sequencing. MS allows precise identification of protein sequencing, to detect the modification of post-translational, and the analysis of complex proteins.
How it’s done:
- Bottom-Up: Proteins are digested into peptides, analyzed by MS, and sequences are reconstructed.
- Top-Down: Intact proteins are analyzed directly, preserving post-translational modifications and isoforms.
Advantages: High-throughput, sensitive, detects modifications, and works on complex mixtures.
Limitations: Requires sophisticated instruments and skilled analysis; top-down is technically challenging for very large proteins.
5. Nanopore Protein Sequencing
It is a newly developed protein sequencing method in which a protein molecule is made to pass through a tiny pore, where the amino acids of the protein molecule produce a unique electrical signal. This method can help scientists to read and detect proteins in real time, but it is still being developed.
How it’s done: Proteins are unfolded and threaded through a nanopore; each amino acid produces a unique ionic current signature.
Advantages: Potential for real-time, single-molecule sequencing and modification detection.
Limitations: Experimental, limited accuracy, and not yet widely applied in routine proteomics.
As biology became more advanced, scientists needed faster and stronger methods to sequence proteins.
The Rise of Mass Spectrometry
A big change came with Mass Spectrometry (MS). Unlike Edman degradation, Mass spectrometry does not remove amino acids one by one. Instead, it measures the mass (weight) of protein pieces very accurately. Computers then figure out the sequence.
How Mass Spectrometry Works?
The protein is broken into smaller pieces.
- These pieces are turned into charged particles.
- The machine measures the mass of each piece.
- A computer compares the data with known sequences to identify the protein.
Two important technologies helped make MS very powerful:
- MALDI (Matrix-Assisted Laser Desorption/Ionization)
- Electrospray Ionization
These two methods gently ionize proteins without destroying them, allowing scientists to study large molecules.
Why Mass Spectrometry Changed Everything?
It brought a revolutionary change in the protein sequencing world as it is fast, can analyze complete protein mixtures instead of a single molecule at a time, a tiny amount of sample is enough, as it is highly sensitive, and it can study thousands of proteins at a time. The most important part is that it gave birth to proteomics.
Proteomics is the study of proteins in a cell, tissue, or organism. Mass spectrometry made proteomics possible because it can handle thousands of proteins in a single experiment. Proteomics is essential because it helps researchers to know which proteins are present in a cell, what their amount is, which of them can be involved in disease formation, and how they interacted for a solution. Proteomics has helped scientists understand diseases like cancer, diabetes, and heart disease.
Modern Advances in Protein Sequencing
Today, protein sequencing is faster and more accurate than ever.
- Tandem Mass Spectrometry (MS/MS) – Breaks protein fragments into smaller pieces and analyzes them twice for higher accuracy.
- High-Resolution Instruments – Can measure mass very precisely, detecting tiny differences between proteins.
- Bioinformatics and Databases – Computers compare mass data with huge protein databases to quickly identify sequences.
- Post-Translational Modifications (PTMs) – Proteins often change after they are made. Modern MS can detect:Phosphorylation, Glycosylation, Acetylation. These modifications are important in diseases like cancer.
While Edman degradation is still used in some cases, mass spectrometry is now the main method in protein research.
Why Protein Sequencing Matters?
It is important because it helps in identifying unknown proteins, supports drug discovery, accurate diagnosis of diseases, and helps scientists to understand how cells work.
Scientists and researchers also use proteomics to identify biomarker proteins that show early signs of disease, helping with early detection and treatment.
Protein sequencing has come a long way. It began with Edman degradation, a careful step-by-step method, and has grown into a powerful, advanced technique called mass spectrometry systems that has the capability to study thousands of proteins at once. Today, Mass Spectrometry is the widely used method to study protein sequencing. This gave rise to proteomics which is one of the crucial fields of biology.
As technology improves, protein sequencing will continue to help us understand life, diagnose diseases, and create new treatments. From slow chemical reactions to advanced machines and computer analysis, the journey of protein sequencing shows how science keeps moving forward step by step, just like the study of proteins, leading to great innovations.
