Early intermediates in the PDI-assisted folding of ribonuclease A

Vinci, F. and Ruoppolo, M. and Pucci, P. and Freedman, R.B. and Marino, G. (2000) Early intermediates in the PDI-assisted folding of ribonuclease A. Protein Science, 9 (3). pp. 525-535. ISSN 0961-8368. (The full text of this publication is not available from this repository)

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Abstract

The oxidative refolding of ribonuclease A has been investigated in several experimental conditions using a variety of redox systems. All these studies agree that the formation of disulfide bonds during the process occurs through a nonrandom mechanism with a preferential coupling of certain cysteine residues. We have previously demonstrated that in the presence of glutathione the refolding process occurs through the reiteration of two sequential reactions: a mixed disulfide with glutathione is produced first which evolves to form an intramolecular S-S bond. In the same experimental conditions, protein disulfide isomerase (PDI) was shown to catalyze formation and reduction of mixed disulfides with glutathione as well as formation of intramolecular S-S bonds. This paper reports the structural characterization of the one-disulfide intermediate population during the oxidative refolding of Ribonuclease A under the presence of PDI and glutathione with the aim of defining the role of the enzyme at the early stages of the reaction. The one-disulfide intermediate population occurring at the early stages of both the uncatalyzed and the PDI-catalyzed refolding was purified and structurally characterized by proteolytic digestion followed by MALDI-MS and LC/ESIMS analyses. In the uncatalyzed refolding, a total of 12 disulfide bonds out of the 28 theoretical possible cysteine couplings was observed, confirming a nonrandom distribution of native and nonnative disulfide bonds. Under the presence of PDT, only two additional nonnative disulfides were detected. Semiquantitative LC/ESIMS analysis of the distribution of the S-S bridged peptides showed that the most abundant species were equally populated in both the uncatalyzed and the catalyzed process. This paper shows the first structural characterization of the one-disulfide intermediate population formed transiently during the refolding of ribonuclease A in quasi-physiological conditions that mimic those present in the ER lumen. At the early stages of the process, three of the foul native disulfides are detected, whereas the Cys26-Cys84 pairing is absent. Most of the nonnative disulfide bonds identified are formed by nearest-neighboring cysteines. The presence of PDI does not significantly alter the distribution of S-S bonds, suggesting that the ensemble of single-disulfide species is formed under thermodynamic control.

Item Type: Article
Uncontrolled keywords: disulfide bond; mass spectrometry; PDI; refolding intermediates; RNase A
Subjects: Q Science > QP Physiology (Living systems) > QP517 Biochemistry
Divisions: Faculties > Science Technology and Medical Studies > School of Biosciences
Depositing User: A. Xie
Date Deposited: 27 May 2009 13:29
Last Modified: 27 May 2009 13:29
Resource URI: http://kar.kent.ac.uk/id/eprint/16708 (The current URI for this page, for reference purposes)
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