Mass spectrometry (MS) provides molecular-level information that is central to the characterization of proteins, peptides, antibodies, and other biologic molecules. Depending on the analytical objective, MS can confirm molecular mass, verify sequence coverage, identify disulfide-linked peptides, localize post-translational modifications (PTMs), and compare product-related variants across samples or process conditions.
As part of our Structural & Physicochemical Characterization platform, Profacgen provides protein mass spectrometry services configured around the molecule, sample matrix, development stage, and required data output. Rather than applying a single workflow to every sample, our scientists select fit-for-purpose intact, subunit, peptide-level, or site-specific analyses and integrate the resulting spectra with complementary chromatographic and biochemical data when appropriate.
Protein molecules are heterogeneous by nature. Translation, processing, expression host biology, purification, formulation, and storage can all introduce structural variants that are not fully described by the coding sequence alone. A measured intact mass can rapidly indicate whether a preparation is consistent with the expected molecular form, while peptide-level tandem mass spectrometry can provide more detailed evidence of sequence identity and modification sites.
Bottom-up LC-MS/MS commonly begins with protein denaturation, reduction and alkylation when appropriate, followed by enzymatic digestion. The resulting peptides are separated by liquid chromatography and analyzed by tandem mass spectrometry. Database searching and manual review are then used to assign peptide sequences and evaluate modifications. Intact and subunit workflows instead preserve larger molecular units and use spectral deconvolution to estimate neutral molecular masses. These approaches answer different questions and are often most informative when used together.
Mass spectrometry does not replace every structural or physicochemical method. For example, secondary and tertiary structure generally require orthogonal techniques such as circular dichroism, fluorescence spectroscopy, differential scanning calorimetry, or other biophysical measurements. Our project design therefore begins with the analytical question rather than the instrument name, helping avoid unnecessary testing while building a coherent characterization package.
Figure 1. Mass Spectrometry-based proteomics. (Shuken, 2023)
Intact Mass & Subunit Analysis
Rapid confirmation of the molecular mass and major molecular forms of purified proteins and biologics.
Peptide Mapping & Sequence Confirmation
Peptide-level LC-MS/MS analysis for sequence coverage, identity confirmation, and localized structural information.
Disulfide Bond & Free-Cysteine Assessment
Non-reducing and reducing workflows designed to evaluate expected disulfide connectivity and investigate selected cysteine-related variants.
PTM & Chemical Modification Analysis
Site-specific identification and relative assessment of modifications that may influence product consistency, stability, or biological performance.
The most useful workflow depends on the question being asked. The table below summarizes common project objectives and the corresponding analytical level. Final method selection is confirmed after review of the protein sequence, molecular format, expected modifications, sample amount, purity, buffer composition, and desired sensitivity.
| Analytical Question | Typical MS Strategy | Representative Output | Related Service |
|---|---|---|---|
| Is the major molecular form consistent with the expected mass? | Intact or subunit mass analysis | Deconvoluted mass, mass difference, major molecular forms | Intact Mass & Subunit Analysis |
| Does the sample contain peptides consistent with the expected sequence? | Bottom-up LC-MS/MS peptide mapping | Identified peptides, sequence coverage, annotated MS/MS evidence | Peptide Mapping |
| Are expected cysteine linkages present? | Non-reducing peptide mapping with comparative reduced analysis | Assigned disulfide-linked peptides and selected variant findings | Disulfide Bond Mapping |
| Where are glycosylation sites and what glycopeptide forms are detected? | Glycopeptide LC-MS/MS, with complementary released-glycan analysis as needed | Site occupancy evidence and site-specific glycoform distribution | Glycosylation Profiling |
| Did storage or stress change oxidation or deamidation levels? | Comparative peptide mapping with targeted modification review | Modified peptide assignments and relative abundance trends | Oxidation & Deamidation Analysis |
| Which proteins change after degrader treatment? | Quantitative proteomics or targeted MS, subject to project design | Protein abundance changes, selectivity profile, dose or time response | Protein Degradation Analysis |
Each project is planned around the required decision rather than a predetermined analytical package. The workflow can be adapted for purified recombinant proteins, monoclonal antibodies, antibody fragments, fusion proteins, enzymes, peptides, glycoproteins, and selected conjugated formats.
Discuss Your Protein MS Project
Deliverables are tailored to the selected module and may include:
Background:
A development team observed a reproducible difference between the theoretical and apparent mass of a purified fusion protein. The team needed to determine whether the difference reflected expected glycosylation, incomplete signal-peptide processing, sequence truncation, or another molecular variant before advancing the construct.
Our Solution:
We designed a tiered workflow beginning with intact mass analysis of the untreated sample, followed by analysis after enzymatic deglycosylation. Bottom-up LC-MS/MS peptide mapping was then used to assess sequence coverage and examine the N-terminal region and predicted glycosylation sites. The results were interpreted together rather than relying on a single observed mass.
Outcome:
The mass change after deglycosylation accounted for most of the observed heterogeneity, while peptide-level data supported the expected mature N-terminus and did not indicate a major truncation. The combined evidence allowed the client to retain the construct and focus subsequent development on controlling glycoform distribution. Results in other projects depend on the molecule, sample quality, and analytical scope.
Background:
A biologics program introduced a change in upstream processing and required a focused comparison of selected molecular attributes between pre-change and post-change material. Particular attention was placed on sequence integrity and chemical modifications that could be influenced by processing and storage history.
Our Solution:
Matched samples were prepared and analyzed within the same LC-MS/MS sequence using a common digestion and data-processing workflow. Peptide maps were compared for sequence coverage, retention behavior, and selected oxidation and deamidation sites. Project-relevant assignments were manually reviewed, and the report separated detected differences from variations below the method's practical interpretive threshold.
Outcome:
The study showed consistent sequence coverage and no new major peptide species in the post-change sample. A small change at one oxidation-sensitive peptide was identified for follow-up with stability data and an orthogonal method. The client used the findings as one component of a broader comparability assessment rather than as stand-alone evidence.
Consult Our Experts on Your Project
References:
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