Structural adaptation of an interacting non-native C-terminal helical extension revealed in the crystal structure of NAD super(+) synthetase from Bacillus anthracis

The crystal structures of NH sub(3)-dependent NAD super(+) synthetase from Bacillus anthracis as the apoenzyme (1.9 A), in complex with the natural catalytic products AMP and pyrophosphate (2.4 A) and in complex with the substrate analog adenosine 5'-( alpha , beta -methylene)triphosphate (2.0...

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Bibliographic Details
Published in:Acta crystallographica. Section D, Biological crystallography. Biological crystallography., 2007-08, Vol.63 (8), p.891-905
Main Authors: McDonald, Heather M, Pruett, Pamela S, Deivanayagam, Champion, Protasevich, Irina I, Carson, WMichael, DeLucas, Lawrence J, Brouillette, Wayne J, Brouillette, Christie G
Format: Article
Language:English
Subjects:
Bacillus anthracis
Escherichia coli
Helicobacter pylori
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Summary:The crystal structures of NH sub(3)-dependent NAD super(+) synthetase from Bacillus anthracis as the apoenzyme (1.9 A), in complex with the natural catalytic products AMP and pyrophosphate (2.4 A) and in complex with the substrate analog adenosine 5'-( alpha , beta -methylene)triphosphate (2.0 A) have been determined. NAD super(+) synthetase catalyzes the last step in the biosynthesis of the vitally important cofactor NAD super(+). In comparison to other NAD super(+) synthetase crystal structures, the C-terminal His-tagged end of the apoenzyme adopts a novel helical conformation, causing significant compensatory changes in the region. The structural accommodations observed in B. anthracis NAD super(+) synthetase are remarkable in the absence of adverse affects on enzyme activity. They also illustrate a rare example of the influence of a non-native C-terminal His-tag extension on the structure of a native protein. In contrast to the apoenzyme, when AMP and pyrophosphate or adenosine 5'-( alpha , beta -methylene)triphosphate are bound, the C-terminus adopts a conformation that allows ATP binding and overall the structure then resembles other NAD super(+) synthetase structures. The structures of NAD super(+) synthetase complexes from B. anthracis are compared with published X-ray crystal structures of the enzyme from B. subtilis, Escherichia coli and Helicobacter pylori. These comparisons support the novel observation that P1 and P2 loop ordering is not a consequence of crystal contacts but rather a consequence of intrinsic intramolecular interactions within the ordered subunit.
ISSN:0907-4449
1399-0047
DOI:10.1107/S0907444907029769