Serum proteomic analyses for probing C3 fragment protein

• Serum proteomics was applied to probe C3 fragments in sera derived from patients with atopic dermatitis (AD).
• Liquid-phase IEF integrating MARC depletion effectively detected the C3 fragment protein in AD sera.
• The C3 complement component was specifically fragmented into C3dg in both extrinsic and intrinsic types of AD.
• C3dg is a putative serum biomarker for AD.

Serum proteomics could provide an opportunity to discover and analyze new factors in human diseases. We attempted to detect a new protein that is dysregulated in sera samples of patients with atopic dermatitis (AD) and to suggest an effective approach to methodologically analyze the serum proteome. We optimized serum proteome analysis in sera derived from patients with AD by integrating several methods, including micro-Rotofor fractionation, 2D-PAGE analysis, and MARC depletion. As a result, the C3dg protein was successfully identified as a new disease-associated factor caused by fragmentation of the C3 complement component in sera of patients with AD. Further Western blotting analyses showed that C3dg was present in the sera of both extrinsic and intrinsic types of AD compared to normal subjects. C3 fragmentation in AD is an interesting topic for further study. The probed fragment of C3 protein, C3dg, could be a candidate biomarker for AD disease detection at the serum level. The present integration methods for serum proteomics are useful and applicable for effective detection of target proteins in other human diseases.

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