Dataset Information

Oxidative folding pathways of bovine milk ?-lactoglobulin with odd cysteine residues.

ABSTRACT: Bovine ?-lactoglobulin (BLG) is a major whey protein with unique structural characteristics: it possesses a free Cys thiol (SH) and two disulfide (SS) bonds and consists of a ?-barrel core surrounded by one long and several short ? helices. Although SS-intact conformational folding has been studied in depth, the oxidative folding pathways and accompanying SS formation/rearrangement are poorly understood. In this study, we used trans-3,4-dihydroxyselenolane oxide, a water-soluble selenoxide reagent which undergoes rapid and quantitative SS formation, to determine the oxidative folding pathways of BLG variant A (BLGA) at pH 8.0 and 25 °C. This was done by characterizing two key one-SS intermediates, a particular folding intermediate having a Cys66-Cys160 SS bond (I-1) and a particular folding intermediate having a Cys106-Cys119 SS bond (I-2), which have a native Cys66-Cys160 and Cys106-Cys119 SS bond, respectively. In the major folding pathway, the reduced protein (R) with abundant ? helices was oxidized to I-1, which was then transformed to I-2 through SS rearrangement. The native protein (N) was formed by oxidation of I-2. The redundant Cys121 thiol facilitates SS rearrangement. N is also generated from an ensemble of folding intermediates having two SS bonds (2SS) intermediates with scrambled SS bonds through SS rearrangement, but this minor pathway is deteriorative due to aggregation or overoxidation of 2SS. During oxidative folding of BLGA, ??? conformational transition occurred as previously observed in SS-intact folding. These findings are informative not only for elucidating oxidative folding pathways of other members of the ?-lactoglobulin family, but also for understanding the roles of a redundant Cys thiol in the oxidative folding process of a protein with odd Cys residues.

SUBMITTER: Iwaoka M

PROVIDER: S-EPMC6668375 | biostudies-literature | 2019 Aug

REPOSITORIES: biostudies-literature

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Oxidative folding pathways of bovine milk β-lactoglobulin with odd cysteine residues.

Iwaoka Michio M Mitsuji Takumi T Shinozaki Reina R

FEBS open bio 20190620 8

Bovine β-lactoglobulin (BLG) is a major whey protein with unique structural characteristics: it possesses a free Cys thiol (SH) and two disulfide (SS) bonds and consists of a β-barrel core surrounded by one long and several short α helices. Although SS-intact conformational folding has been studied in depth, the oxidative folding pathways and accompanying SS formation/rearrangement are poorly understood. In this study, we used trans-3,4-dihydroxyselenolane oxide, a water-soluble selenoxide reage ...[more]

PMID: 31087497

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Project description:Although bovine beta-lactoglobulin assumes a monomeric native structure at pH 3 in the absence of salt, the addition of salts stabilizes the dimer. Thermodynamics of the monomer-dimer equilibrium dependent on the salt concentration were studied by sedimentation equilibrium. The addition of NaCl, KCl, or guanidine hydrochloride below 1 M stabilized the dimer in a similar manner. On the other hand, NaClO(4) was more effective than other salts by about 20-fold, suggesting that anion binding is responsible for the salt-induced dimer formation, as observed for acid-unfolded proteins. The addition of guanidine hydrochloride at 5 M dissociated the dimer into monomers because of the denaturation of protein structure. In the presence of either NaCl or NaClO(4), the dimerization constant decreased with an increase in temperature, indicating that the enthalpy change (DeltaH(D)) of dimer formation is negative. The heat effect of the dimer formation was directly measured with an isothermal titration calorimeter by titrating the monomeric beta-lactoglobulin at pH 3.0 with NaClO(4). The net heat effects after subtraction of the heat of salt dilution, corresponding to DeltaH(D), were negative, and were consistent with those obtained by the sedimentation equilibrium. From the dependence of dimerization constant on temperature measured by sedimentation equilibrium, we estimated the DeltaH(D) value at 20 degrees C and the heat capacity change (DeltaC(p)) of dimer formation. In both NaCl and NaClO(4), the obtained DeltaC(p) value was negative, indicating the dominant role of burial of the hydrophobic surfaces upon dimer formation. The observed DeltaC(p) values were consistent with the calculated value from the X-ray dimeric structure using a method of accessible surface area. These results indicated that monomer-dimer equilibrium of beta-lactoglobulin at pH 3 is determined by a subtle balance of hydrophobic and electrostatic effects, which are modulated by the addition of salts or by changes in temperature.

Dataset Information

Oxidative folding pathways of bovine milk ?-lactoglobulin with odd cysteine residues.

Publications

Oxidative folding pathways of bovine milk β-lactoglobulin with odd cysteine residues.

Similar Datasets

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