Quantitative evaluation of the role of cysteine and methionine residues in the antioxidant activity of human serum albumin using recombinant mutants

Abstract

SummaryThe importance of cysteine (Cys) and methionine (Met) residues for the antioxidant activity of human serum albumin (HSA) was investigated using recombinant HSA mutants, in which Cys34 and/or the six Met residues had been mutated to Ala. The scavenging activities of the mutants against five reactive oxygen and nitrogen species were evaluated by a chemiluminescence assay, electron paramagnetic resonance spectroscopy, or a HPLC-flow reactor assay. Our results showed that the contributions of Cys34 and the Met residues to the antioxidant activity of HSA were 61% and 29% against O 2 2, 68% and 61% against H 2 O 2 , 38% and 6% against HO , 36% and 13% against HOCl, and 51% and 1% against NO, respectively. Thus, the findings propose in a direct way that Cys34 plays a more important role than the Met residues in the antioxidant activity of HSA.2012 IUBMB IUBMB Life, 64(5): [450][451][452][453][454] 2012

Amino acids of importance for the antioxidant activity of human serum albumin as revealed by recombinant mutants and genetic variants

“…3). This finding is in accordance with that of Iwao et al [19], who registered only 40% activity of the recombinant mutant C34A. If the free Cys residue was placed in another position in HSA, then it could probably also have an antioxidant effect; however, its new molecular environment could affect its antioxidant effect.…”

“…HSA has six Met residues (Fig. 1), and a previous study from our laboratory revealed that mutating all six Mets to alanines resulted in diminished antioxidant activity against H 2 O 2 and four other types of ROS [19]. The investigation also revealed that Cys34 plays a more important role than the other Met residues for the antioxidant activities of HSA.…”

“…Several lines of evidence propose that HSA is the major and predominant antioxidant in plasma [4,19,29]. Although the six Mets contribute to this function, it is mainly based on the presence of Cys34.…”

“…To investigate whether the molecular environment of a Cys residue can have an impact on its antioxidant activity, we have also studied the antioxidant capacities of two albumins with an additional Cys residue, namely an albumin with a C177F mutation, which results in a free Cys in position 169, and a mutant with an R410C substitution. In addition to Cys residues, the presence of methionine residues (Met) is important for the antioxidant activity of a protein [19]. However, it seems to be an open question whether other amino acid residues can contribute significantly to this protein function.…”

Cryptic epitopes and functional diversity in extracellular proteins

“…It also influences fluid distribution of tissues providing 75% of the intravascular oncotic pressure (Doweiko and Nompleggi, 1991). Additional functions include a role in acid-base physiology owing to its 16 histidine imidazole residues (Agrafiotis et al, 2014;Watson, 1999), anti-oxidant properties by neutralising oxygen radicals (Anraku et al, 2013;Bruschi et al, 2013;Iwao et al, 2012), anticoagulation properties (Galanakis, 1992;Stoffersen, 1979, 1980), and the binding and transport of ligands (Anand and Mukherjee, 2013;Dalvit et al, 2002;Sarver et al, 2005).…”