| How is the serum proteome changed by the removal of albumin? Does albumin bind proteins or peptides in a manner specific to pathology? These questions are important considerations for the proteomics field, where removal of albumin from serum samples is routine. In an effort to address these questions, the proteins removed from serum using a chemically based albumin depletion method were examined, catalogued, and characterized. The combination of size exclusion and affinity chromatography with mass spectrometry allowed for an in-depth probe into the proteins, and their associations, of the albumin-enriched fraction. One hundred and twenty proteins were identified in the albumin-enriched fraction of human serum. Thirty four of these proteins were found to be associated with albumin, either directly or indirectly, and they include both high and low abundance proteins, intact proteins and protein fragments. Additionally, proteins that are co-purified along with albumin were also identified. Interestingly, sixty two proteins identified here were not observed in the counterpart albumin-depleted fraction. The findings that albumin is specifically binding proteins has important ramifications for future proteomics studies and biomarker discovery. The biological role of albumin may play a vital role in affecting free-state serum levels, and therefore detection, of biomarkers. Furthermore, preliminary investigations indicate that the albumin-enriched fraction of human serum will be useful in biomarker discovery efforts, especially those concerning cardiovascular disease. Consequently, although the albumin-enriched fraction is expected to vary among different albumin depletion methods, it is essential that these fractions are thoroughly examined for bound and co-purified proteins. |
