Identification of an active dimeric intermediate populated during the unfolding process of the cambialistic superoxide dismutase from Streptococcus mutans |
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Authors: | Merlino Antonello Russo Krauss Irene Rossi Bianca Vergara Alessandro De Vendittis Alberto Marco Salvatore De Vendittis Emmanuele Sica Filomena |
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Affiliation: | Dipartimento di Chimica, Università di Napoli Federico II, Complesso Universitario Monte S. Angelo, Via Cinthia, I-80126 Naples, Italy; Istituto di Biostrutture e Bioimmagini, CNR, Via Mezzocannone 16, I-80134 Naples, Italy. |
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Abstract: | Superoxide dismutases are enzymes that protect biological systems against oxidative damage caused by superoxide radicals. In this paper, a detailed characterization is presented on the stability of SmSOD, the dimeric cambialistic superoxide dismutase from the dental pathogenic microorganism Streptococcus mutans, towards temperature and guanidine hydrochloride. Thermal and chemical denaturations were investigated by means of circular dichroism, fourth-derivative UV spectroscopy and fluorescence measurements. Data indicate that SmSOD is endowed with a significant thermostability and that both its thermal and guanidine hydrochloride-induced unfolding processes occur through a three-state model, characterized by a catalytically active dimeric intermediate species. To our knowledge, SmSOD is the smallest known dimeric protein that populates a well-structured active dimeric rather than a monomeric intermediate during unfolding processes. |
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Keywords: | Superoxide dismutase Thermal stability Chemical stability Dimeric intermediate Unfolding |
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