A structurally driven analysis of thiol reactivity in mammalian albumins

Abstract

Understanding the structural basis of protein redox activity is still an open question. Hence, by using a structural genomics approach, different albumins have been chosen to correlate protein structural features with the corresponding reaction rates of thiol exchange between albumin and disulfide DTNB. Predicted structures of rat, porcine, and bovine albumins have been compared with the experimentally derived human albumin. High structural similarity among these four albumins can be observed, in spite of their markedly different reactivity with DTNB. Sequence alignments offered preliminary hints on the contributions of sequence-specific local environments modulating albumin reactivity. Molecular dynamics simulations performed on experimental and predicted albumin structures reveal that thiolation rates are influenced by hydrogen bonding pattern and stability of the acceptor C34 sulphur atom with donor groups of nearby residues. Atom depth evolution of albumin C34 thiol groups has been monitored during Molecular Dynamic trajectories. The most reactive albumins appeared also the ones presenting the C34 sulphur atom on the protein surface with the highest accessibility. High C34 sulphur atom reactivity in rat and porcine albumins seems to be determined by the presence of additional positively charged amino acid residues favoring both the C34 S⁻ form and the approach of DTNB.

Reversible Disulfide Formation of the Glutamate Carboxypeptidase II Inhibitor E2072 Results in Prolonged Systemic Exposures In Vivo

“…The differences between the two species suggest more interactions of E2072 with plasma albumins/proteins probably by formation of reversible proteinthiol-mixed disulfides in rodents compared with primates. Such species differences in plasma albumin reactivity have been described previously (Spiga et al, 2011). It is likely that both the homodisulfide and the mixed disulfides formed in vivo serve as a reversible depot of E2072 and help to maintain the monomer in circulation, which results in its prolonged pharmacological effects.…”

The thiol of human serum albumin: Acidity, microenvironment and mechanistic insights on its oxidation to sulfenic acid

“…Fourth, not only the Cys34 thiol does ionize but also other neighboring residues do (e.g. Asp38, His39 and Tyr84) whose ionization states may affect the former [33,34]. In connection to this, it has been shown that Tyr84Phe and His39Leu mutations have a profound impact on Cys34 reactivity with DTNB, in a way not completely understood yet [33].…”

Quantification of Global Protein Disulfides and Thiol-Protein Mixed Disulfides to Study the Protein Dethiolation Mechanisms

“…The dethiolation processes of XSSP of albumin [21,22] and the notions regarding the mechanisms of thiol exchange reactions [38] are useful for a better prediction of the processes of PSSP dethiolation.…”

“…On the contrary the reactions (2) and (3) express different thermodynamic tendencies that are identifiable on the basis of the leaving groups. These groups are those thiols that in thiol exchange reactions of XSSP and have the lowest pKa value [21,22], namely XSH in reactions (2) or (4), or PSH in reaction (3), respectively. Similar considerations can be used to predict the PSSP dethiolation via thiol exchange reactions.…”

“…After the cellular XSSP and PSSP production, the return to PSH is characterized by rather complex molecular events of deglutathionylation. The dethiolation of albumin mixed disulfides [20,21] is paradigmatic for a better comprehension of the mechanisms of thiol exchange processes occurring at cellular level [20,21]. Albumin has only one free Cys residue (Cys34) with a low pKa value (of about 5 -7), that in dependence of pKa difference of thiols of XSSP may be equally well transformed nonenzymatically into PSH, by reaction (3) (if pKa of PSH < pKa of XSH) or into a new thiol-protein mixed disulfide (X'SSP), equivalent to reaction (2), (if pKa of PSH > pKa of XSH) [20,21]:…”