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J. Biol. Chem., Vol. 277, Issue 38, 34785-34792, September 20, 2002

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Molecular, Biochemical, and Functional Characterization of a Nudix Hydrolase Protein That Stimulates the Activity of a Nicotinoprotein Alcohol Dehydrogenase^*

Harm Kloosterman, Jan W. Vrijbloed^§, and Lubbert Dijkhuizen^¶

From the Department of Microbiology, Groningen Biomolecular Sciences and Biotechnology Institute (GBB), University of Groningen, Kerklaan 30, 9751 NN Haren, The Netherlands

The cytoplasmic coenzyme NAD⁺-dependent alcohol (methanol) dehydrogenase (MDH) employed by Bacillus methanolicus during growth on C₁-C₄ primary alcohols is a decameric protein with 1 Zn²⁺-ion and 1-2 Mg²⁺-ions plus a tightly bound NAD(H) cofactor per subunit (a nicotinoprotein). Mg²⁺-ions are essential for binding of NAD(H) cofactor in MDH protein expressed in Escherichia coli. The low coenzyme NAD⁺-dependent activity of MDH with C₁-C₄ primary alcohols is strongly stimulated by a second B. methanolicus protein (ACT), provided that MDH contains NAD(H) cofactor and Mg²⁺-ions are present in the assay mixture. Characterization of the act gene revealed the presence of the highly conserved amino acid sequence motif typical of Nudix hydrolase proteins in the deduced ACT amino acid sequence. The act gene was successfully expressed in E. coli allowing purification and characterization of active ACT protein. MDH activation by ACT involved hydrolytic removal of the nicotinamide mononucleotide NMN(H) moiety of the NAD(H) cofactor of MDH, changing its Ping-Pong type of reaction mechanism into a ternary complex reaction mechanism. Increased cellular NADH/NAD⁺ ratios may reduce the ACT-mediated activation of MDH, thus preventing accumulation of toxic aldehydes. This represents a novel mechanism for alcohol dehydrogenase activity regulation.

The nucleotide sequence(s) reported in this paper has been submitted to the GenBank^TM/EBI Data Bank with accession number(s) AY128667.

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