A next generation setup for pre-fractionation of non-denatured proteins reveals diverse albumin proteoforms each carrying several post-translational modifications

Proteomic biomarker search requires the greatest analytical reproducibility and detailed information on altered proteoforms. Our protein pre-fractionation applies orthogonal native chromatography and conserves important features of protein variants such as native molecular weight, charge and major glycans. Moreover, we maximized reproducibility of sample pre-fractionation and preparation before mass spectrometry by parallelization and automation. In blood plasma and cerebrospinal fluid (CSF), most proteins, including candidate biomarkers, distribute into a multitude of chromatographic clusters. Plasma albumin, for example, divides into 15-17 clusters. As an example of our technique, we analyzed these albumin clusters from healthy volunteers and from dogs and identified cluster-typical modification patterns. Renal disease further modifies these patterns. In human CSF, we found only a subset of proteoforms with fewer modifications than in plasma. We infer from this example that our method can be used to identify and characterize distinct proteoforms and, optionally, enrich them, thereby yielding the characteristics of proteoform-selective biomarkers.