Stabilization of active-site loops in NH3-dependent NAD+ synthetase from Bacillus subtilis.
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Devedjiev Y, Symersky J, Singh R, Jedrzejas M, Brouillette C, Brouillette W, Muccio D, Chattopadhyay D, DeLucas L
Stabilization of active-site loops in NH3-dependent NAD+ synthetase from Bacillus subtilis.
Acta Crystallogr D Biol Crystallogr. 2001 Jun;57(Pt 6):806-12. Epub 2001 May 25.
- PubMed ID
- 11375500 [ View in PubMed]
- Abstract
The NH(3)-dependent NAD(+) synthetase (NADS) participates in the biosynthesis of nicotinamide adenine dinucleotide (NAD(+)) by transforming nicotinic acid adenine dinucleotide (NaAD) to NAD(+). The structural behavior of the active site, including stabilization of flexible loops 82-87 and 204-225, has been studied by determination of the crystal structures of complexes of NADS with natural substrates and a substrate analog. Both loops are stabilized independently of NaAD and solely from the ATP-binding site. Analysis of the binding contacts suggests that the minor loop 82-87 is stabilized primarily by a hydrogen bond with the adenine base of ATP. Formation of a coordination complex with Mg(2+) in the ATP-binding site may contribute to the stabilization of the major loop 204-225. The major loop has a role in substrate recognition and stabilization, in addition to the protection of the reaction intermediate described previously. A second and novel Mg(2+) position has been observed closer to the NaAD-binding site in the structure crystallized at pH 7.5, where the enzyme is active. This could therefore be the catalytically active Mg(2+).