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A conserved arginine plays a role in the catalytic cycle of the protein disulphide isomerases

par Lappi, Anna Kaisa;Lensink, Marc ;Alanen, Heli H.I.;Salo, Kirsi E H;Lobell, Mario;Juffer, André A.H.;Ruddock, Lloyd L.W.
Référence Journal of Molecular Biology, 335, 1, page (283-295)
Publication Publié, 2004-01

Article révisé par les pairs

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Résumé :

The pKa values of the CXXC active-site cysteine residues play a critical role in determining the physiological function of the thioredoxin superfamily. To act as an efficient thiol-disulphide oxidant the thiolate state of the N-terminal cysteine must be stabilised and the thiolate state of the C-terminal cysteine residue destabilised. While increasing the pKa value of the C-terminal cysteine residue promotes oxidation of substrates, it has an inhibitory effect on the reoxidation of the enzyme, which is promoted by the formation of a thiolate at this position. Since reoxidation is essential to complete the catalytic cycle, the differential requirement for a high and a low pKa value for the C-terminal cysteine residue for different steps in the reaction presents us with a paradox. Here, we report the identification of a conserved arginine residue, located in the loop between β5 and α4 of the catalytic domains of the human protein disulphide isomerase (PDI) family, which is critical for the catalytic function of PDI, ERp57, ERp72 and P5, specifically for reoxidation. An examination of the published NMR structure for the a domain of PDI combined with molecular dynamic studies suggest that the side-chain of this arginine residue moves into and out of the active-site locale and that this has a very marked effect on the pKa value of the active-site cysteine residues. This intra-domain motion resolves the apparent dichotomy of the pKa requirements for the C-terminal active-site cysteine. © 2003 Elsevier Ltd. All rights reserved.