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Biochemistry. 2008 Sep 23;47(38):10227-39. doi: 10.1021/bi800767t. Epub 2008 Aug 26.

Plasmodium falciparum Sir2 is an NAD+-dependent deacetylase and an acetyllysine-dependent and acetyllysine-independent NAD+ glycohydrolase.

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1
Department of Pharmacology, Weill Cornell College of Medicine, 1300 York Avenue LC216, New York, New York 10065, USA.

Abstract

Sirtuins are NAD (+)-dependent enzymes that deacetylate a variety of cellular proteins and in some cases catalyze protein ADP-ribosyl transfer. The catalytic mechanism of deacetylation is proposed to involve an ADPR-peptidylimidate, whereas the mechanism of ADP-ribosyl transfer to proteins is undetermined. Herein we characterize a Plasmodium falciparum sirtuin that catalyzes deacetylation of histone peptide sequences. Interestingly, the enzyme can also hydrolyze NAD (+). Two mechanisms of hydrolysis were identified and characterized. One is independent of acetyllysine substrate and produces alpha-stereochemistry as established by reaction of methanol which forms alpha-1- O-methyl-ADPR. This reaction is insensitive to nicotinamide inhibition. The second solvolytic mechanism is dependent on acetylated peptide and is proposed to involve the imidate to generate beta-stereochemistry. Stereochemistry was established by isolation of beta-1- O-methyl-ADPR when methanol was added as a cosolvent. This solvolytic reaction was inhibited by nicotinamide, suggesting that nicotinamide and solvent compete for the imidate. These findings establish new reactions of wildtype sirtuins and suggest possible mechanisms for ADP-ribosylation to proteins. These findings also illustrate the potential utility of nicotinamide as a probe for mechanisms of sirtuin-catalyzed ADP-ribosyl transfer.

PMID:
18729382
PMCID:
PMC2732577
DOI:
10.1021/bi800767t
[Indexed for MEDLINE]
Free PMC Article

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