TAILIEUCHUNG - Báo cáo khoa học: Ataxin-3 is subject to autolytic cleavage

The protein ataxin-3 is responsible for spinocerebellar ataxia type 3, a neu-rodegenerative disease triggered when the length of a stretch of consecutive glutamines exceeds a critical threshold. Different physiologic roles have been suggested for this protein. More specifically, recent papers have shown that the highly conserved N-terminal Josephin domain of ataxin-3 binds ubiquitin and has ubiquitin hydrolase activity, thanks to a catalytic device specific to cysteine proteases. | ỊFEBS Journal Ataxin-3 is subject to autolytic cleavage Pier Luigi Mauri1 Matteo Riva2 Daniela Ambu1 Antonella De Palma1 Francesco Secundo3 Louise Benazzi1 Marco Valtorta2 Paolo Tortora2 and Paola Fusi2 1 Istituto di Tecnologie Biomediche CNR Milano Italy 2 Dipartimento di Biotecnologie e Bioscienze Universita di Milano-Bicocca Milano Italy 3 Istituto di Biocatalisi e Riconoscimento molecolare delCNR Milano Italy Keywords ataxin-3 mass spectrometry polyglutamine diseases proteolysis Correspondence P. Tortora Dipartimento di Biotecnologie e Bioscienze University di Milano-Bicocca Piazza della Scienza 2 I-20126 Milano Italy Fax 39 02 6448 3565 Tel 39 02 6448 3401 E-mail These authors contributed equally to this work Received 21 February 2006 revised 15 July 2006 accepted 20 July 2006 doi The protein ataxin-3 is responsible for spinocerebellar ataxia type 3 a neu-rodegenerative disease triggered when the length of a stretch of consecutive glutamines exceeds a critical threshold. Different physiologic roles have been suggested for this protein. More specifically recent papers have shown that the highly conserved N-terminal Josephin domain of ataxin-3 binds ubiquitin and has ubiquitin hydrolase activity thanks to a catalytic device specific to cysteine proteases. This article shows that the protein also has autoproteolytic activity sustained by the same residues responsible for the ubiquitin hydrolase activity. The autolytic activity was abolished when these residues . Cys14 and His119 were replaced by noncatalytic ones. Furthermore we found that pretreatment of the protein with tosyl L-phe-nylalanine chloromethyl ketone also abolished this activity and that this site-specific reagent covalently bound His119 findings supported by MS experiments. MS also allowed us to establish that the attack was aspecific as cleavage sites were observed at the carboxyl side of apolar acidic and polar uncharged residues .

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