Sinoacutine

J Biol Chem. 2009 Sep 25;284(39):26758-67.

Removal of substrate inhibition and increase in maximal velocity in the short chain dehydrogenase/reductase salutaridine reductase involved in morphine biosynthesis.[Pubmed: 19648114]

METHODS AND RESULTS:
Sinoacutine reductase (SalR, EC 1.1.1.248) catalyzes the stereospecific reduction of Sinoacutine to 7(S)-salutaridinol in the biosynthesis of morphine. In addition, a specific role in Sinoacutine binding by either hydrogen bond formation or hydrophobic interactions was assigned to each amino acid. Substrate docking also revealed an alternative mode for Sinoacutine binding, which could explain the strong substrate inhibition of Sinoacutine reductase. An alternate arrangement of Sinoacutine in the enzyme was corroborated by the effect of various amino acid substitutions on substrate inhibition. In most cases, the complete removal of substrate inhibition was accompanied by a substantial loss in enzyme activity. However, some mutations greatly reduced substrate inhibition while maintaining or even increasing the maximal velocity.
CONCLUSIONS:
Based on these results, a double mutant of Sinoacutine reductase was created that exhibited the complete absence of substrate inhibition and higher activity compared with wild-type Sinoacutine reductase.

J Nat Prod. 2005 Jul;68(7):1128-30.

Morphinane alkaloids with cell protective effects from Sinomenium acutum.[Pubmed: 16038566 ]

METHODS AND RESULTS:
One new morphinane alkaloid, sinomenine N-oxide (1), and one new natural occurring morphinane alkaloid, N-demethylsinomenine (2), together with six known alkaloids, 7,8-didehydro-4-hydroxy-3,7-dimethoxymorphinan-6-ol (3), sinomenine (4), Sinoacutine (5), N-norSinoacutine, acutumine, and acutumidine, were isolated from the stems of Sinomenium acutum. Their structures were elucidated on the basis of spectroscopic analysis and chemical methods.
CONCLUSIONS:
Compounds 2, 3, and 5 have protective effects against hydrogen peroxide-induced cell injury.

J Biol Chem. 2009 Sep 4;284(36):24432-42.

CYP719B1 is salutaridine synthase, the C-C phenol-coupling enzyme of morphine biosynthesis in opium poppy.[Pubmed: 19567876]

The C-C phenol-coupling reaction along the biosynthetic pathway to morphine in opium poppy is catalyzed by the cytochrome P450-dependent oxygenase Sinoacutine synthase.
METHODS AND RESULTS:
We report herein on the identification of Sinoacutine synthase as a member of the CYP719 family of cytochromes P450 during a screen of recombinant cytochromes P450 of opium poppy functionally expressed in Spodoptera frugiperda Sf9 cells. Recombinant CYP719B1 is a highly stereo- and regioselective enzyme; of forty-one compounds tested as potential substrates, only (R)-reticuline and (R)-norreticuline resulted in formation of a product (Sinoacutine and norsalutaridine, respectively).

J Biol Chem. 2011 Feb 25;286(8):6532-41.

Atomic structure of Sinoacutine reductase from the opium poppy (Papaver somniferum).[Pubmed: 21169353]

The opium poppy (Papaver somniferum L.) is one of the oldest known medicinal plants. In the biosynthetic pathway for morphine and codeine, salutaridine is reduced to salutaridinol by salutaridine reductase (SalR; EC 1.1.1.248) using NADPH as coenzyme.
METHODS AND RESULTS:
Here, we report the atomic structure of SalR to a resolution of ∼1.9 Å in the presence of NADPH. The core structure is highly homologous to other members of the short chain dehydrogenase/reductase family. The major difference is that the nicotinamide moiety and the substrate-binding pocket are covered by a loop (residues 265-279), on top of which lies a large "flap"-like domain (residues 105-140). This configuration appears to be a combination of the two common structural themes found in other members of the short chain dehydrogenase/reductase family. Previous modeling studies suggested that substrate inhibition is due to mutually exclusive productive and nonproductive modes of substrate binding in the active site. This model was tested via site-directed mutagenesis, and a number of these mutations abrogated substrate inhibition. However, the atomic structure of SalR shows that these mutated residues are instead distributed over a wide area of the enzyme, and many are not in the active site.
CONCLUSIONS:
To explain how residues distal to the active site might affect catalysis, a model is presented whereby SalR may undergo significant conformational changes during catalytic turnover.