Cut precisely, see clearly — The art of selecting mass spectrometry-grade sequencing enzymes

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In mass spectrometry (MS)-based proteomics research, the "bottom-up" strategy dominates.

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Precision Cuts for Clear Views — The Art of Selecting Mass Spectrometry-Grade Sequencing Enzymes

In mass spectrometry (MS)-based proteomics research, the "bottom-up" strategy dominates. The core step of this strategy involves digesting complex protein mixtures into peptides, which are then separated, identified, and quantified via liquid chromatography-tandem mass spectrometry (LC-MS/MS). In this workflow, the selection and quality of proteolytic enzymes directly determine the depth, accuracy, and reproducibility of downstream data. Mass spectrometry-grade sequencing enzymes are specially prepared and purified protein hydrolase formulations designed to meet the demands of high-sensitivity, high-precision mass spectrometry analysis. They have become indispensable foundational tools in modern proteomics.

I. Major Mass Spectrometry-Grade Sequencing Enzymes and Their Characteristics

1. Trypsin — The Gold Standard

Trypsin (UA070137) is a highly specific serine protease that cleaves at the carboxyl terminus of lysine (Lys, K) and arginine (Arg, R) residues. However, it generally does not cleave when the cleavage site is immediately followed by proline (i.e., K/R-P sequences). The peptide lengths and hydrophobicity produced by trypsin are ideally suited for chromatographic separation and mass spectrometric fragmentation, making it the most commonly used enzyme in proteomics experiments.

Trypsin has earned its status as the "gold standard" because the peptides it generates exhibit ideal charge characteristics and fragmentation behavior in mass spectrometry—peptide carboxyl termini carry strong charges, enabling efficient ionization. Additionally, trypsin is widely sourced (traditionally extracted from porcine pancreas) and can now be obtained through recombinant expression. Recombinant trypsin is free of animal-derived components, eliminating the risk of animal-derived viral contamination and naturally lacks chymotrypsin activity.

Mass spectrometry-grade trypsin is typically treated with TPCK to eliminate chymotrypsin activity and chemically modified (e.g., methylation) to reduce autolysis. Modern recombinant trypsin can also be further stabilized through site-directed mutagenization to prevent self-cleavage. High-quality mass spectrometry-grade trypsin achieves over 95% specificity for cleavage at the C-termini of lysine and arginine.

Enzyme Brand	Proteins Identified	Peptides Identified	Missed Cleavage Rate
Imported T	3753	18355	39.02%
UA070130	4154	18608	18.64%
UA070137	4161	17510	14.69%
Domestic Competitor	4082	17929	14.24%

2. Lysyl Endopeptidase (Lys-C) — The Ideal Partner for Trypsin

Lysyl endopeptidase (Lys-C) (UA070140), derived from Achromobacter lyticus, is a serine protease that highly specifically cleaves peptide bonds at the carboxyl side of lysine residues.

Lys-C complements trypsin: while trypsin cleaves lysine less efficiently than arginine, Lys-C specifically targets lysine. Using the two enzymes together significantly reduces missed cleavage sites. More importantly, Lys-C can cleave lysine-proline sequences (K-P), which trypsin cannot effectively cleave. Thus, a sequential digestion strategy—first with Lys-C, followed by trypsin—can dramatically improve digestion efficiency and sequence coverage.

Another advantage of Lys-C is that the peptides it generates often exhibit higher charge states, making them ideal for electron transfer dissociation (ETD) fragmentation. Lys-C also demonstrates unique value in applications like phosphopeptide enrichment, as its peptides carry primary amines at both N- and C-termini, enabling dual labeling. Lys-C achieves over 90% specificity for lysine cleavage.

Sample	BSA Digested Peptides	BSA Coverage	0 Missed Cleavages Rate	≥2 Missed Cleavages Rate
Control 50:1	145	91.43%	50.34%	17.24%
UA 50:1	159	92.09%	42.14%	22.64%
UA 25:1	158	90.28%	47.47%	18.35%

3. Chymotrypsin — Expanding Hydrophobic Region Coverage

Chymotrypsin (UA070088) is a serine endopeptidase that primarily cleaves at the carboxyl terminus of aromatic amino acids such as phenylalanine (Phe, F), tryptophan (Trp, W), and tyrosine (Tyr, Y), and can also cleave leucine (Leu, L) with lower efficiency.

Chymotrypsin's specificity is orthogonal to trypsin, making it uniquely effective in regions where trypsin cannot provide adequate coverage—particularly hydrophobic protein regions and transmembrane domains. Studies show that supplementing trypsin digestion with chymotrypsin digestion increases the number of detected amino acids by approximately 40% on average. For certain proteins (e.g., catalase), coverage improvements can exceed 90%.

4. Glu-C Protease — Glutamate/Aspartate-Specific Cleavage

Glu-C protease (also known as V8 protease) (UA070059) is derived from Staphylococcus aureus and specifically cleaves at the carboxyl terminus of glutamate (Glu, E) and aspartate (Asp, D) residues. In phosphate buffer, the enzyme can also cleave aspartate, while in ammonium/acetate buffer, it primarily cleaves glutamate.

The unique peptides generated by Glu-C can cross-validate trypsin digestion results, improving protein identification confidence and aiding in post-translational modification (PTM) localization. In studies requiring comprehensive protein sequence coverage from multiple angles, Glu-C serves as a valuable complementary tool.

5. PNGase F — Cleaving N-Linked Glycans on Glycoproteins

Glycan structures on glycoproteins are complex and highly heterogeneous, which can severely suppress mass spectrometry signals and complicate spectral interpretation. Removing glycans with PNGase F (UA070041) significantly reduces sample complexity, allowing researchers to analyze deglycosylated proteins or peptides more clearly.

The intact N-glycans released by PNGase F can be directly separated and analyzed via liquid chromatography (HPLC) or mass spectrometry (MS) to study glycan composition and structure. After glycan removal, the hydrophobic core regions of proteins may become more exposed, improving the digestion efficiency of proteases (e.g., trypsin), increasing the number of identified peptides, and enhancing overall sequence coverage.

II. Strategies for Selecting Mass Spectrometry-Grade Sequencing Enzymes

1. Routine Analysis: Trypsin as the First Choice

For routine proteomic qualitative and relative/absolute quantitative analysis, trypsin alone typically suffices. The peptides it produces are of moderate length, exhibit high ionization efficiency, and yield easily interpretable spectra, making trypsin the most mature and database-compatible option available today.

2. Enhancing Coverage: Multi-Enzyme Combination Strategies

When target protein sequences are unknown or maximal sequence coverage is required, a combination of multiple proteases should be employed alongside de novo sequencing strategies to achieve complete protein sequence assembly. Common combination strategies include:

- Trypsin + Lys-C: Digest first with Lys-C, followed by trypsin, to significantly reduce missed cleavage sites.
- Trypsin + Chymotrypsin: Complement regions inaccessible to trypsin, particularly hydrophobic domains.
- Trypsin + Glu-C: Generate overlapping peptides from different cleavage sites to improve identification confidence.

Digestion Enzyme	Competitor A-Trypsin	Competitor B-Trypsin	UA-Trypsin	UA-Mix (Trypsin+Lys-C)
Digestion Time	8h	8h	8h	4h
Protein Count	86.34%	92.55%	91.31%	100.00%
Peptide Count	95.62%	100.00%	91.70%	96.95%
Missed Cleavage Rate	34.40%	27.30%	23.30%	16.90%

III. Conclusion

Mass spectrometry-grade sequencing enzymes are foundational tools in proteomics research. From the "gold standard" trypsin to diverse alternative enzyme families, from traditional animal-derived extraction to modern recombinant expression, from single overnight digestions to multi-enzyme combinations, rapid digestion, and immobilized enzyme technologies—this field continues to evolve, expanding the boundaries of mass spectrometry analysis. Understanding the characteristics, strengths, and limitations of each enzyme type and selecting and combining them appropriately based on research objectives are key to obtaining high-quality proteomics data. As novel proteases and digestion technologies emerge, mass spectrometry-grade sequencing enzymes will continue to play an irreplaceable central role in protein identification, biomarker discovery, biopharmaceutical characterization, and de novo protein sequencing.

This article is reviewed and published by the technical expert team of UA

Disclaimer: This article partially utilizes artificial intelligence assistance in its creation. If any content involves copyright or intellectual property issues, please let us know and we promise to verify and remove it as soon as possible.

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