TAILIEUCHUNG - Báo cáo khoa học: Characterization of monomeric substates of ascorbate oxidase

Ascorbate oxidase (AAO) is a large, multidomain, dimeric protein whose folding⁄unfolding pathway is characterized by a complex, multistep pro-cess. Here we used fluorescence correlation spectroscopy to demonstrate the formation of partially folded monomers by pH-induced full dissociation into subunits. | IFEBS Journal Characterization of monomeric substates of ascorbate oxidase Al I l-s 1 _2 _ Ai. I I Al I 1 M I l . 12 A . II l Al I Almerinda Di Venere Eleonora Nicolai Nicola Rosato Antonello Rossi Alessandro Finazzi Agro2 and Giampiero Mei1 2 1 NAST Centre University of Rome Tor Vergata Italy 2 Department of ExperimentalMedicine and BiochemicalSciences University of Rome Tor Vergata Italy Keywords dimeric proteins fluorescence correlation spectroscopy folding intermediates high pressure Correspondence G. Mei Department of Experimental Medicine and BiochemicalSciences University of Rome Tor Vergata Via Montpellier 1 00133 Rome Italy Fax 39 06 72596468 Tel 39 06 72596460 E-mail mei@ These authors contributed equally to this work Received 30 November 2010 revised 10 February 2011 accepted 23 February 2011 Ascorbate oxidase AAO is a large multidomain dimeric protein whose folding unfolding pathway is characterized by a complex multistep process. Here we used fluorescence correlation spectroscopy to demonstrate the formation of partially folded monomers by pH-induced full dissociation into subunits. Hence the structural features of monomeric AAO could be studied by fluorescence and CD spectroscopy. We found that the monomers keep their secondary structure whereas subtle conformational changes in the tertiary structure become apparent. AAO dissociation has also been studied when unfolding the protein by high hydrostatic pressure at different pH values. A strong protein concentration dependence was observed at pH 8 whereas the enzyme was either monomeric or dimeric at pH 10 and 6 respectively. The calculated volume change associated with the unfolding of monomeric AAO DV -55 mL-mol-1 is in the range observed for most proteins of the same size. These findings demonstrate that partially folded monomeric species might populate the energy landscape of AAO and that the overall AAO stability is crucially controlled by a few quaternary interactions at .

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