What is label-free quantification in proteomics?
In research, quantitative analysis is a key means to reveal the dynamic changes of biological processes, identify differential proteins, and explore disease mechanisms. Compared to labeled quantification methods (such as SILAC, iTRAQ, TMT), Label-Free Quantification (LFQ) has gradually become the mainstream choice in recent years due to its simplicity, adaptability, and lower cost. Especially when handling clinical samples, large-scale cohorts, or valuable materials that cannot be labeled, LFQ shows irreplaceable advantages. With the continuous development of high-resolution mass spectrometry technology and data analysis algorithms, the accuracy and reproducibility of label-free quantification have also been significantly improved.
1. What is Label-Free Quantification (LFQ)?
Label-Free Quantification is a protein quantification method based on mass spectrometry signal intensity (MS1) or spectral counting. Compared to labeled methods such as SILAC and TMT, LFQ does not require the introduction of any external tags before sample processing, thus offering higher throughput and sample compatibility.
The two common label-free quantification methods include:
- MS1 intensity quantification: By extracting the chromatographic peak area of peptides at the MS1 level, comparing the abundance changes of the same peptide in different samples.
- Spectral Counting: Counting the number of MS/MS spectra in which a specific protein is detected in different samples, used as an approximate value of protein abundance.
2. Core principles of label-free quantification
The premise of label-free quantification is that under the same mass spectrometry acquisition conditions, the MS signal intensity of the same peptide is proportional to its relative abundance in the sample.
The key steps are as follows:
1. Sample proteolysis: Breaking down proteins into peptides;
2. Liquid Chromatography-Mass Spectrometry (LC-MS/MS): Online separation and detection of peptides;
3. Peptide identification and quantification: Using software like MaxQuant or Proteome Discoverer to extract peak areas or spectral counts;
4. Cross-sample alignment and normalization: Achieving accurate comparison between different samples by aligning chromatographic retention times, mass deviations, etc.
3. Advantages of label-free quantification
1. Simplified sample processing workflow
No need for isotope or reagent labeling, reducing experimental complexity and cost.
2. Higher sample throughput
Can be freely expanded to dozens or hundreds of samples, suitable for large-scale cohort studies.
3. Strong adaptability to sample types
Applicable to various sample types such as cells, tissues, and body fluids, especially clinical and precious samples.
4. Increasing sensitivity
Thanks to advances in high-resolution mass spectrometry platforms (e.g., Orbitrap Exploris 480), the accuracy and coverage of LFQ quantification have significantly improved.
4. Challenges and solutions of label-free quantification
Despite its many advantages, LFQ also faces the following challenges:
1. Batch-to-batch variation and data drift
Systematic errors may be introduced by different batches of LC-MS runs.
Solution: Betapack Biotechnology employs strict QC strategies and internal standard calibration mechanisms, combined with Retention Time Alignment and Normalization algorithms, to enhance data consistency.
2. Missing values and quantification accuracy
The same peptide may not be detected in different samples, leading to 'missing value' issues.
Solution: We use MaxQuant's Match Between Runs feature and data-driven missing value imputation strategies to retain as much quantitative information as possible.
3. High dependence on instrument stability
LFQ requires higher performance from mass spectrometry platforms.
Solution: Betapack Biotechnology is equipped with high-throughput nanoflow LC-MS systems and performs daily instrument quality control to ensure consistency and stability in long-term operations.
5. Detailed LFQ technical workflow
The following is the standard workflow for label-free quantitative proteomics service by Betapack Biotechnology:
1. Sample processing
- Protein extraction → Quantification → In-gel/out-gel digestion
- Optional high-pH peptide fractionation to increase depth
2. LC-MS/MS analysis
- High-resolution Orbitrap mass spectrometry platform
- Using DDA or DIA mode (supporting LFQ quantification)
3. Data analysis
- Peptide and protein identification (FDR<1%)
- Relative quantification based on MS1 intensity
- Differential protein screening (Fold Change, p-value)
- GO/KEGG pathway enrichment analysis
6. Typical applications of label-free quantification
- Disease mechanism research: Identifying disease-related proteins and exploring potential targets
- Drug mechanism of action: Comparing protein expression differences in treatment/control groups
- Phenotype association analysis: Revealing expression changes under different cell/tissue states
- Clinical Cohort Study: Analyzing Differential Expression Patterns in Large-Scale Clinical Samples
Label-free quantification is one of the most widely used and flexible quantification techniques in current proteomics research. With its simple process, high throughput capability, and continuously optimized data algorithms, it is becoming an important bridge between basic research and clinical translation. If you are looking for a stable and reliable LFQ proteomics service platform, please contact our technical experts for personalized solutions and project recommendations.
Biotape Parker Biotechnology - A quality service provider for bioproduct characterization and multi-omics mass spectrometry testing
Related Services:
How to order?
