Structural and functional insights into S-thiolation of human serum albumins

Abstract

Human serum albumin (HSA) is the most abundant serum protein, contributing to the maintenance of redox balance in the extracellular fluids. One single free cysteine residue at position 34 is believed to be a target of oxidation. However, the molecular details and functions of oxidized HSAs remain obscure. Here we analyzed serum samples from normal subjects and hyperlipidemia patients and observed an enhanced S-thiolation of HSA in the hyperlipidemia patients as compared to the control individuals. Both cysteine and homocysteine were identified as the low molecular weight thiols bound to the HSAs. Intriguingly, S-thiolations were observed not only at Cys34, but also at multiple cysteine residues in the disulfide bonds of HSA. When the serum albumins from genetically modified mice that exhibit high levels of total homocysteine in serum were analyzed, we observed an enhanced S-homocysteinylation at multiple cysteine residues. In addition, the cysteine residues in the disulfide bonds were also thiolated in recombinant HSA that had been treated with the disulfide molecules. These findings and the result that S-homocysteinylation mediated increased surface hydrophobicity and ligand binding activity of HSA offer new insights into structural and functional alternation of serum albumins via S-thiolation.

Thiol disulfide exchange reactions in human serum albumin: the apparent paradox of the redox transitions of Cys34

“…In a very recent study, it has been observed that only in the presence of pathological levels of fatty acids, cysteines different from Cys 34 can form mixed disulfides with cysteine or homocysteine [23]. ribonuclease, phospholipase, aldolase, etc.…”

“…Only in a recent study, the presence of albumin with mixed disulfides involving other protein cysteines like Cys 90 , and Cys 112 in hyper-lipidemic patients was discovered [23]; indeed, even partial disruption of its disulfide bridges could represent a dramatic event as such albumin undergoes deleterious aggregation and amyloid polymerization [24]. Only in a recent study, the presence of albumin with mixed disulfides involving other protein cysteines like Cys 90 , and Cys 112 in hyper-lipidemic patients was discovered [23]; indeed, even partial disruption of its disulfide bridges could represent a dramatic event as such albumin undergoes deleterious aggregation and amyloid polymerization [24].…”

“…The involvement of some of the 17 natural disulfides in redox changes of albumin has been never described or verified in the plasma of healthy subjects. Only in a recent study, the presence of albumin with mixed disulfides involving other protein cysteines like Cys 90 , and Cys 112 in hyper-lipidemic patients was discovered [23]; indeed, even partial disruption of its disulfide bridges could represent a dramatic event as such albumin undergoes deleterious aggregation and amyloid polymerization [24]. It is thus interesting to verify whether the most active low molecular mass reducing compound in serum, that is, free cysteine really interacts exclusively with the mixed disulfide of Cys 34 in spite of the presence of 17 times more abundant protein disulfides.…”

“…ribonuclease, phospholipase, aldolase, etc. In a very recent study, it has been observed that only in the presence of pathological levels of fatty acids, cysteines different from Cys 34 can form mixed disulfides with cysteine or homocysteine [23]. It is possible that the binding of multiple fatty acids to albumin induces a steric tension which turns away the two cysteines once the original bridge has been disrupted.…”

Testing for Ketoprofen Binding to HSA Coated Magnetic Nanoparticles under Normal Conditions and after Oxidative Stress

“…According to literature reports, aromatic amino acids (tryptophan and tyrosine) and sulfur-containing amino acids (cysteine and methionine) are the places most susceptible to oxidizing agents. Under the conditions of oxidative stress, the formation of dimeric structures of aromatic amino acids and the formation of disulfide bonds between amino acids containing sulfur occurs in these places [7]. Moreover, the polypeptide chain may be denatured.…”