High-Resolution Protein Correlation Profiling (PCP)-MS Service

Q: Can PCP-MS distinguish between direct and indirect interactions?

PCP-MS identifies proteins that co-fractionate in the same physical assembly. While it confirms membership in a complex, it does not distinguish direct contact from "guilt-by-association." For direct contact mapping, we recommend integration with our XL-MS platform.

Q: How do you separate true interactors from random co-elution?

We use a three-layered strategy: 1) High-resolution fractionation (80+ fractions) to sharpen peaks; 2) Target-decoy permutation testing for strict FDR control (<1%); 3) Cross-referencing against databases like CORUM and IntAct.

Q: Is PCP-MS compatible with membrane-bound complexes?

Yes. We utilize optimized "mild" detergents (e.g., Digitonin or DDM) that preserve membrane-associated complexes while effectively solubilizing them for SEC-HPLC.

Q: Can I perform PCP-MS on non-model organisms?

Absolutely. Since PCP-MS is antibody-free and tag-free, it only requires a sequenced genome for peptide identification, making it ideal for unique plants, microbes, or rare animal models.

Q: What is the minimum sample requirement?

We typically recommend ~1 × 10^8 cells or 300-500 mg tissue per replicate to ensure sufficient signal across 80 fractions. Contact us for high-sensitivity micro-fractionation options.

Q: Can we detect dynamic changes, such as drug effects?

Yes, this is a core strength. Differential PCP-MS observes "peak shifts," indicating protein dissociation or recruitment into new complexes following treatment.

Q: How does PCP-MS handle transient or weak interactions?

It is generally more sensitive than Co-IP for transient interactions because it avoids stringent washing. The use of near-native buffers throughout SEC maximizes the retention of low-affinity partners.

The High-Resolution Protein Correlation Profiling (PCP)-MS Service is an antibody-free interactomics platform used to systematically map native protein complexes. By combining ultra-high-resolution SEC fractionation with quantitative mass spectrometry, this service identifies co-eluting proteins to reconstruct endogenous interaction networks. Deliverables include validated proteome-wide correlation matrices, interaction hub maps, and high-fidelity protein elution profiles.

Key Specifications

Profiling >1,000 native protein complexes in a single run.
Antibody-free and tag-free endogenous interactome mapping.
High-resolution separation using 50–80+ SEC fractions.
Quantitative Orbitrap™ MS identification of >8,000 proteins.
Analysis-ready Cytoscape-compatible interaction network files.

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What is PCP-MS?

In the cellular metropolis, proteins rarely work as lone agents; they assemble into sophisticated molecular machines. While traditional proteomics identifies "who" is present, Protein Correlation Profiling Mass Spectrometry (PCP)-MS reveals "who is working with whom" in their near-native state.

The core logic of PCP-MS is based on the principle of co-fractionation. When a native (non-denatured) cell lysate is passed through high-resolution Size Exclusion Chromatography (SEC), proteins that are physically bound together elute in the same fractions. By analyzing every fraction via quantitative mass spectrometry and applying deconvolution algorithms, we reconstruct the global interactome map without the artifacts associated with overexpression or chemical cross-linking.

$PCP-MS Co-fractionation Principle: Test tube complexes passing through SEC column resulting in overlapping 2D line graph of protein intensity.$

Figure 1. The principle of PCP-MS Co-fractionation. Native complexes are separated by SEC, and subunits belonging to the same complex demonstrate perfectly overlapping elution profiles.

What Problems Can PCP-MS Solve?

For decades, researchers have relied on Co-IP or Y2H. PCP-MS bridges critical gaps in large-scale discovery:

The "Orphan" Protein Problem: Perfect for targets lacking high-quality antibodies or sensitive to tagging. PCP-MS is entirely antibody-free and tag-free.
System-Wide Discovery: Instead of testing one-by-one, a single run provides a "top-down" snapshot of the interactome, discovering novel members of complexes.
Mapping Transient Dynamics: Sensitive enough to detect how complex stoichiometry shifts in response to drugs, viruses, or disease.
Near-Native Characterization: Avoids harsh washing steps, preserving weak or transient interactions often lost in standard assays.

Key Advantages: Why Partner with Us?

Ultra-High Resolution Fractionation

We use Agilent 1260 II HPLC to collect 50–80+ fractions per sample (vs standard 30-40), providing a 40% improvement in statistical power and eliminating random co-elution noise.

Industry-Leading ID Depth

Coupled with Thermo Scientific™ Orbitrap™ Eclipse™, we routinely identify >8,000 endogenous proteins, including low-abundance transcription factors.

Publication-Ready Reproducibility

Standardized non-denaturing lysis ensures technical consistency (R² > 0.92). For higher spatial resolution, we offer integrated XL-MS capabilities.

Strict FDR Control (< 1%)

We apply permutation-based False Discovery Rate (FDR) filters at the complex level, ensuring downstream validation is based on high-confidence data.

Technical Services

Service Scope Tech Comparison Workflow Platform Sample Requirements Deliverables FAQ Get a Custom Proposal

Our PCP-MS Service Portfolio

Global Proteome-Wide Discovery

A comprehensive "landscape" view of the total cell or tissue interactome.
Ideal for generating new biological hypotheses and mapping unknown pathways.
Identifies thousands of native complexes in a single experiment.

Differential Interactome Profiling

The gold standard for mechanism-of-action (MoA) studies.
Compares complex assembly across states (e.g., Drug vs. Control, WT vs. Mutant).
Identifies specific "network rewiring" events and peak shifts.

Organelle-Enriched PCP-MS

Focused profiling of purified mitochondria, nuclei, or lysosomes.
Increases sensitivity for organelle-specific machineries by reducing cytosolic background.
Requires optimized fractionation protocols prior to SEC.

Advanced Data Deconvolution

Bioinformatics-only service for existing co-fractionation MS data.
Application of optimized in silico pipelines (PrInCE, CCMS algorithms).
Extracts deeper biological insights from complex raw data sets.

Strategic Selection: Is PCP-MS Right for Your Research?

Feature	PCP-MS	Co-IP MS	BioID / Proximity
Discovery Strategy	Global (Top-down) Discovery of 1000+ complexes	Targeted (Bait-specific) Validation	Neighborhood (Proximal) Mapping
Antibody / Tag	None (Antibody-free & Tag-free)	High-quality Antibody required	Fusion Tag required (e.g., BirA*)
Native State	Near-Native (Excellent)	Moderate (Post-lysis isolation)	Superior (Captured in living cells)
Transient PPIs	Moderate (Better than Co-IP)	Poor (Lost in stringent washes)	Excellent (Covalent biotinylation)
Sample Input	High (10⁸ cells / 300mg tissue)	Medium (10⁷ cells)	Medium (Requires transfection)
Unknown Discovery	Excellent (De novo PPI mapping)	Limited to bait interactors	Good for local neighborhood
Best Use Case	System-wide atlas & MoA studies	Validating specific pairs	Membrane & insoluble proteins

Precision Workflow: From Native Fractionation to MS Discovery

Near-Native Extraction

Samples are lysed using optimized, non-denaturing buffers tailored to cell/tissue type.
Ionic detergents are avoided to maintain physical protein-protein bonds.

High-Resolution SEC Fractionation

Lysate separation on Agilent 1260 II HPLC using high-res SEC columns (separation up to 5 MDa).
Collection of 50–80+ fractions in a temperature-controlled environment.

Quantitative Mass Spectrometry

Digestion and analysis via TMT (Tandem Mass Tag) or Label-Free Quantification (LFQ).
High scan speed Orbitrap analysis ensures maximum coverage across the gradient.

Correlation Analysis

Calculation of Pearson correlation coefficient (r) for co-elution similarity:
r = Σ (x_i - x̄)(y_i - ȳ) / √ [ Σ (x_i - x̄)² Σ (y_i - ȳ)² ]
Comparison of elution profiles to identify overlapping peaks.

Bioinformatics & Network Clustering

Clustering using PrInCE or CCMS algorithms to identify functional modules.
Mapping against databases like CORUM and IntAct.

Instrumentation and Platform Capabilities

Orbitrap™ Eclipse™ & Exploris™ for Deep Interactome Mapping

To achieve the absolute sensitivity required for deep interactome mapping, our laboratory utilizes top-tier analytical tools. The high scan speed and sensitivity are critical for quantifying low-abundance complex members across 80+ fractions.

MS Platforms: Thermo Scientific™ Orbitrap™ Eclipse™ Tribrid™ and Exploris™ 480.
Resolution: Up to 500,000 FWHM for accurate precursor separation.
HPLC Systems: Agilent 1260 Infinity II HPLC for high-precision, automated fractionation with minimized carryover.

Strict QC & Deconvolution

Component	Function	Standard
Fractionation Resolution	Separation power	50-80+ Fractions per sample
Technical Replicates	Ensure consistency	R² > 0.92 reproducibility
FDR Control	Remove false positives	< 1% at Complex-level (Permutation test)
Database Mapping	Validation	Cross-ref with CORUM / IntAct

Thermo Scientific Orbitrap Eclipse

Sample Requirements & Technical Compatibility

Sample Submission Guidelines

Sample Type	Recommended Amount	Preparation Notes
Cell Pellets	1 × 10⁸ cells	Wash with PBS 3x; snap-freeze in liquid nitrogen.
Tissues	300 - 500 mg	Minimize blood contamination; flash-freeze immediately.
Purified Organelles	1 - 2 mg protein	Isolate via non-denaturing gradients or magnetic beads.
Shipping Requirement: All samples must be shipped on dry ice to prevent the dissociation of temperature-sensitive complexes.

Deliverables: Data Packages and Reports

Data & Matrices

Raw MS Data: Complete .raw files for all 80+ fractions ensuring transparency.
Cleaned Elution Profiles: Interactive Excel table (.xlsx) with quantified intensities.
Correlation Matrix: Prioritized list of pairs with correlation scores and p-values.

Visualization & Reporting

Network Visualization: Cytoscape-compatible graphs highlighting hubs and modules.
Comprehensive Report: Detailed PDF with methodology, QC metrics (fractionation reproducibility), and biological summary.

Global Correlation Matrix (Heatmap)

A proteome-wide 2D correlation matrix (typically 8,000 x 8,000 proteins). Clusters along the diagonal represent stable, endogenous protein machineries (e.g., Proteasome).

High-Resolution Co-elution Curves

Zoom-in views of specific complexes. Ribosome members show perfectly synchronized peaks across 80 fractions, providing physical evidence of association.

Differential Stoichiometry Analysis

Visualizing "peak shifts" in control vs. treated groups. A shift in a protein’s profile indicates drug-induced dissociation or change in assembly.

Interaction Network Topology

Cytoscape-compatible circular maps where proteins are nodes and correlation coefficients are edges, highlighting functional hubs and "bridge" proteins.

FAQ: PCP-MS Interactomics

Can PCP-MS distinguish between direct and indirect interactions?

A. PCP-MS identifies proteins that co-fractionate in the same physical assembly. While it confirms membership in a complex, it does not distinguish direct contact from "guilt-by-association." For direct contact mapping, we recommend integration with our XL-MS platform.

How do you separate true interactors from random co-elution?

A. We use a three-layered strategy: 1) High-resolution fractionation (80+ fractions) to sharpen peaks; 2) Target-decoy permutation testing for strict FDR control (<1%); 3) Cross-referencing against databases like CORUM and IntAct.

Is PCP-MS compatible with membrane-bound complexes?

A. Yes. We utilize optimized "mild" detergents (e.g., Digitonin or DDM) that preserve membrane-associated complexes while effectively solubilizing them for SEC-HPLC.

Can I perform PCP-MS on non-model organisms?

A. Absolutely. Since PCP-MS is antibody-free and tag-free, it only requires a sequenced genome for peptide identification, making it ideal for unique plants, microbes, or rare animal models.

What is the minimum sample requirement?

A. We typically recommend ~1 × 10⁸ cells or 300-500 mg tissue per replicate to ensure sufficient signal across 80 fractions. Contact us for high-sensitivity micro-fractionation options.

Can we detect dynamic changes, such as drug effects?

A. Yes, this is a core strength. Differential PCP-MS observes "peak shifts," indicating protein dissociation or recruitment into new complexes following treatment.

How does PCP-MS handle transient or weak interactions?

A. It is generally more sensitive than Co-IP for transient interactions because it avoids stringent washing. The use of near-native buffers throughout SEC maximizes the retention of low-affinity partners.

References

Kristensen, A. R., et al. (2012). "A dynamic map of native protein assemblies." Nature Methods.
Heusel, M., et al. (2019). "Complex-centric proteome profiling by SEC-SWATH-MS." Molecular & Cellular Proteomics.
Skinnider, M. A., et al. (2021). "PrInCE: an R/Bioconductor package for protein-protein interaction network inference." Bioinformatics.
Mallam, A. L., et al. (2019). "Systematic mammalian protein complex-ome profiling." Cell Reports.