Affinity Purification-Mass Spectrometry Service

What Is Affinity Purification-Mass Spectrometry?

Affinity Purification-Mass Spectrometry (AP-MS) identifies proteins associated with a known bait protein. Target-specific antibodies or affinity tags, such as FLAG, GFP, and Strep, enrich the bait and co-purifying proteins from biological samples. The enriched material is digested and analyzed by LC-MS/MS, followed by protein database searching.

 

Unlike global proteomics, AP-MS focuses on bait-associated proteins to investigate potential interaction partners, protein complexes, and condition-dependent changes. Co-purification indicates an association but does not, by itself, prove direct protein-protein binding. The recovered proteins may interact directly with the bait, belong to the same complex, or represent nonspecific background. Appropriate controls are therefore essential when evaluating candidates.

Low, T. Y. et al. Cell. Mol. Life Sci. 2021.

Figure 1. Common Affinity Purification Methods: IP (A) and Tag-Based Purification (B)

AP-MS Service at MtoZ Biolabs

MtoZ Biolabs supports AP-MS projects based on research goals, available bait materials, and sample enrichment status. Our services include:

1. Identification of Affinity-Enriched Proteins

LC-MS/MS identification of proteins from IP/Pull-Down beads, eluates, or gel bands to support candidate interactor screening.

2. Tag-Based AP-MS

Evaluation of enrichment and identification strategies for samples containing FLAG-, GFP-, or Strep-tagged bait proteins, including projects lacking suitable bait-specific IP antibodies.

3. Comparative AP-MS

Relative abundance comparison of bait-associated proteins between experimental conditions when suitable controls and replicates are available.

 

For project assessment, provide the bait identity, tag or antibody information, sample source, enrichment status, controls, and experimental groups. These details help distinguish projects requiring upstream affinity enrichment from those ready for downstream LC-MS/MS identification. Tag-based enrichment also requires consideration of whether the tag affects bait localization, function, or complex formation.

Choose the Right AP-MS Workflow

Research Need	Recommended Workflow
Identify partners of a tagged bait protein	Tag-Based AP-MS
Study bait associations without a suitable IP antibody, using an available tagged bait	FLAG-, GFP-, or Strep-Based AP-MS
Investigate endogenous bait associations with a suitable IP antibody	Co-IP-MS
Compare bait-associated proteins before and after treatment	Comparative AP-MS with controls and replicates
Compare complexes associated with wild-type and mutant bait proteins	Comparative Tag-Based AP-MS, assessing bait expression and enrichment

Sample Submission Requirements

We accept gel bands, IP/Pull-Down beads, eluates, and selected loading buffer-treated solutions. Original cells, tissues, microorganisms, or body fluids require workflow assessment before submission.

Sample Type	Recommended Requirements	Storage and Shipping
Gel Band	Visible band; provide staining method and group information	Room temperature or ice packs, as appropriate
Bead-Bound Samples	Specify bead type, enrichment, washing conditions, and controls	Snap-freeze in liquid nitrogen; ship on dry ice
Eluate / Protein Solution	≥20 µg total protein, >0.5 µg/µL; provide buffer composition	Snap-freeze in liquid nitrogen; ship on dry ice
Loading Buffer-Treated Solution	Provide buffer formulation for compatibility assessment	Confirm shipping requirements before submission

Avoid degraded samples and excessive salts or detergents. Protein solutions should contain less than 0.1% SDS; contact us before submitting samples with higher concentrations or unusual buffers. Protein identification requires an appropriate reference sequence database; custom databases may be supplied for non-model organisms.

 

Please identify each sample and its corresponding control clearly. Samples showing severe protein degradation, or containing unresolved high-salt or high-detergent contamination, may be unsuitable for analysis.

Service Advantages

1. Flexible Sample Acceptance

Analyze gel bands, beads, and protein solutions without unnecessarily repeating completed enrichment steps.

 

2. Bait-Oriented Assessment

Select an approach based on available antibodies, affinity tags, sample status, and research objectives.

 

3. High-Resolution Identification

Use Orbitrap high-resolution mass spectrometry and protein database searching for protein and peptide identification.

 

4. One-Time Charge

Our pricing is transparent, with no hidden fees or additional costs.

 

Case Studies

Case 1. Flavivirus-Host Protein Interaction Mapping

Shah et al. used AP-MS to compare Dengue and Zika virus-associated host protein networks, identifying shared and virus-specific associations. Subsequent functional experiments examined selected host factors involved in viral replication and pathogenesis, demonstrating how AP-MS supports virus-host interaction research.

Shah, P. S. et al. Cell. 2018.

Figure 2. DENV-human Protein-Protein Interaction Network Analysis

Case 2. Interaction Analysis of Streptococcal M1 Protein

Torres-Sangiao et al. combined AP-MS and quantitative mass spectrometry to study interactions between Streptococcus pyogenes M1 protein, plasma proteins, and antibodies. They reported 292 significantly enriched IgG-associated peptides representing 56 IgG chains in the immunized group. The study indicated that polyclonal anti-M1 IgG predominantly recognized epitopes outside other plasma protein-binding interfaces, illustrating how AP-MS can examine immune-related changes in protein associations.

Torres-Sangiao, E. et al. Mol. Cell Proteomics. 2024.

Figure 3. M1 Protein Affinity-Purification of Human and Mouse Plasma Proteins

Deliverables

1. Raw MS Data

Original mass spectrometry files.

2. Protein and Peptide Identification Results

Excel tables with identification details, sequence coverage, scores, and available intensity values.

3. Analysis Report

PDF describing the samples, analytical methods, and main findings.

Relative abundance comparisons are available when supported by the study design and data. Protein identification and enrichment evidence should be interpreted alongside matched negative controls and bait recovery levels; a higher co-purified protein signal does not necessarily indicate stronger binding.

 

FAQs

Q1. Can AP-MS be used to study weak or transient protein interactions?

AP-MS more readily preserves stable associations. Weak or transient interactions may be lost during purification, requiring optimized conditions or complementary approaches.

 

Q2. Do candidate interaction partners identified by AP-MS require further validation?

Yes, when direct binding must be demonstrated. AP-MS identifies co-purifying candidate proteins but does not establish direct interactions.

 

Q3. Can quantitative analysis be performed in AP-MS experiments?

Yes. Relative quantification can compare bait-associated protein abundance between conditions. Controls and replicates are recommended; abundance changes do not directly measure binding affinity.

 

Contact Us

Planning an AP-MS study? MtoZ Biolabs combines affinity purification strategies with high-resolution LC-MS/MS for candidate interactor identification, protein complex analysis, and comparative profiling.

Contact us with your bait, sample type, enrichment status, and research objectives to discuss a suitable AP-MS analysis strategy and sample submission plan.

MtoZ Biolabs, an integrated chromatography and mass spectrometry (MS) services provider.

Related Services

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Co-Immunoprecipitation Protein Interaction Analysis Service

Pull-Down Assay Service