Structural stability of Human serum albumin is modified in rheumatoid arthritis

Abstract

Differential scanning calorimetry (DSC) can interrogate changes in structure and/or concentration of the most abundant proteins in a biological sample via heat denaturation curves (HDCs). In blood serum for example, HDC changes are a result of either concentration or altered thermal stabilities for 7-10 proteins and has previously been shown capable of differentiating between sick and healthy human subjects. Here, we compare HDCs and proteomic profiles of 50 patients experiencing joint-inflammatory symptoms, 27 of which were clinically diagnosed with rheumatoid arthritis (RA). The HDC of all 50 subjects appeared significantly different from expected healthy curves, but comparison of additional differences between the RA the non-RA subjects allowed more specific understanding of RA samples. We used mass spectrometry (MS) to investigate the reasons behind the additional HDC changes in RA patients. The HDC differences do not appear to be directly related to differences in the concentrations of abundant serum proteins. Rather, the differences can be attributed to modified thermal stability of the most abundant protein, human serum albumin (HSA). By quantifying differences in the frequency of artificially induced post translational modifications (PTMs), we found that HSA in RA subjects had a much lower surface accessibility, indicating potential ligand or protein binding partners in certain regions that could explain the shift in HSA melting temperature in the RA HDCs. Several low abundance proteins were found to have significant changes in concentration in RA subjects and could be involved in or related to binding of HSA. Certain amino acid sites clusters were found to be less accessible in RA subjects, suggesting changes in HSA structure that may be related to changes in protein-protein interactions. These results all support a change in behavior of HSA which may give insight into mechanisms of RA pathology.

Quantifying In Situ Structural Stabilities of Human Blood Plasma Proteins Using a Novel Iodination Protein Stability Assay

“…Moreover, it is difficult to apply thermal denaturation methods on blood serum, the most common biological source for diagnosis. This is because serum albumin (HSA), the most abundant serum protein, has a relatively high melting temperature , and thus reduces the efficiency of the temperature gradient to aggregate the proteins using thermal cyclers currently commercially available. , Removing HSA prior to thermal denaturation is not a viable answer as that may alter many other proteins’ PFS because HSA also stabilizes many serum proteins. The second general type of MS-based methods use chemical modification which can measure the PFS of different residues across the protein sequence.…”