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Abstract: SA-PO1100

Post-Translational Modifications of Albumin Causes a Decreased Binding Capacity of Hydrophobic Metabolites

Session Information

Category: Pathology and Lab Medicine

  • 1502 Pathology and Lab Medicine: Clinical

Authors

  • Jankowski, Vera, University hospital RWTH Aachen, Aachen, Germany
  • Noels, Heidi, RWTH University Aachen, Aachen, Germany
  • Jankowski, Joachim, RWTH Aachen, Aachen, BE, Germany
Background

Since post-translational modifications of proteins may have an impact on the pathogenesis of diseases like atherosclerosis or chronic kidney disease (CKD), post-translational modifications are currently gaining increasing interest. In this study, a comprehensive method for analysis ofpost-translational modifications is established for the clinical diagnostic routine.

Methods

Here, we analysed albumin isolated from CKD patients and healthy controls by chromatographic steps and identified by mass-spectrometry. Post-translational modifications of albumin were identified after digestion by analysing mass-signal shifts of albumin peptides using pertinent mass-databases.

Results

Albumin isolated from plasma of CKD patients but not from healthy control subjects was specifically post-translationally modified by guanidylation of lysines at positions 249, 468, 548, 565 and 588. After identification of guanidylations as post-translational modifications of albumin isolated from CKD patients, these modifications were quantified by mass-spectrometry demonstrating a significant increase in the corresponding mass-signal intensities in CKD patients compared to healthy controls. The relative amount of guanidylation of lysine at position 468 in CKD patients was determined as 63 ± 32 % (N=3). In-vitro guanidylation of albumin from healthy control subjects caused a decreased binding capacity of albumin in a time-dependent manner. Binding of indoxyl sulfate (protein bound fraction) decreased from 82 ± 1 % of non post-translationally modified albumin to 56 ± 1 % after in-vitro guanidylation (p < 0.01) whereas the binding of tryptophan decreased from 20 to 4%. These results are in accordance with the binding of indoxyl sulfate to albumin from healthy control subjects and CKD patients (88 ± 3 vs. 74 ± 10, p < 0.01). Thus, in-vitro post-translational guanidylation of albumin had a direct effect on the binding capacity of hydrophobic metabolites like indoxyl sulfate and tryptophan.

Conclusion

We used a mass spectrometry-based method for the characterisation of post-translational modification and demonstrated the pathophysiological impact of a representative post-translational modification of plasma albumin. The data described in this study may help to elucidate the pathophysiological role of protein modifications.