Probing the two-metal ion mechanism in the restriction endonuclease BamHI

Letif Mones, Petr Kulhánek, Jan Florián, István Simon, Monika Fuxreiter

Research output: Contribution to journalArticle

21 Citations (Scopus)

Abstract

The choreography of restriction endonuclease catalysis is a long-standing paradigm in molecular biology. Bivalent metal ions are required almost for all PD..D/ExK type enzymes, but the number of cofactors essential for the DNA backbone scission remained ambiguous. On the basis of crystal structures and biochemical data for various restriction enzymes, three models have been developed that assign critical roles for one, two, or three metal ions during the phosphodiester hydrolysis. To resolve this apparent controversy, we investigated the mechanism of BamHI catalysis using quantum mechanical/molecular mechanical simulation techniques and determined the activation barriers of three possible pathways that involve a Glu-113 or a neighboring water molecule as a general base or an external nucleophile that penetrated from bulk solution. The extrinsic mechanism was found to be the most favorable with an activation free energy of 23.4 kcal/mol, in reasonable agreement with the experimental data. On the basis of the effect of the individual metal ions on the activation barrier, metal ion A was concluded to be pivotal for the reaction, while the enzyme lacking metal ion B still has moderate efficiency. Thus, we propose that the catalytic scheme of BamHI does not involve a general base for nucleophile generation and requires one obligatory metal ion for catalysis that stabilizes the attacking nucleophile and coordinates it throughout the nucleophilic attack. Such a model may also explain the variation in the number of metal ions in the crystal structures and thus could serve as a framework for a unified catalytic scheme of type II restriction endonucleases.

Original languageEnglish
Pages (from-to)14514-14523
Number of pages10
JournalBiochemistry
Volume46
Issue number50
DOIs
Publication statusPublished - Dec 18 2007

ASJC Scopus subject areas

  • Biochemistry

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