Transcriptome analysis of Leucojum aestivum and identification of genes involved in norbelladine biosynthesis

Transcriptome analysis of Leucojum aestivum led to the identification of 50 key genes associated with Amaryllidaceae alkaloid biosynthesis including norbelladine synthase which localized in the cytosol and catalyzed norbelladine formation. The Amaryllidaceae alkaloids (AAs) are a large group of plant specialized metabolites, which are known for their biological activities. Although the general chemical reactions in the AA biosynthetic pathway have been proposed, the genes and enzymes of the pathway remain largely unstudied. All AAs are synthesized from a common precursor, norbelladine, by the condensation of tyramine and 3,4-dihydroxybenzaldehyde. The enzyme norbelladine synthase (NBS) which catalyzes the condensation reaction has only been characterized at a molecular level from one species, and the subcellular localizations have not been explored. Hence, the intracellular compartments wherein the AAs are biosynthesized remain unknown. In this study, a first comprehensive transcriptomic analysis of summer snowflake (Leucojum aestivum) was done to identify key genes associated with AA biosynthesis. Fifty orthologous genes were identified and deposited into GenBank. In addition, we identified and further characterized NBS from the transcriptome of L. aestivum and previously reported Narcissus papyraceus. Phylogenetic analysis showed that LaNBS, NpNBS1 and NpNBS2 shared high amino acid identity. The heterologous expression of LaNBS produced a recombinant protein with NBS activity. Bioinformatic prediction and C-terminal GFP tagging in transiently transformed Nicotiana benthamiana showed that LaNBS, NpNBS1 and NpNBS2 were likely localized to the cytosol which suggests that the AA biosynthesis starts in the cytosol. This study provides an Amaryllidaceae transcriptome that will be very helpful to identify genes for characterization studies in AA metabolism in planta or using heterologous systems. In addition, our study will facilitate the bioengineering of AA biosynthetic pathway in plants or in microorganisms.

Cloning and characterization of norbelladine synthase catalyzing the first committed reaction in Amaryllidaceae alkaloid biosynthesis

BACKGROUND

Amaryllidaceae alkaloids (AAs) are a large group of plant-specialized metabolites displaying an array of biological and pharmacological properties. Previous investigations on AA biosynthesis have revealed that all AAs share a common precursor, norbelladine, presumably synthesized by an enzyme catalyzing a Mannich reaction involving the condensation of tyramine and 3,4-dihydroxybenzaldehyde. Similar reactions have been reported. Specifically, norcoclaurine synthase (NCS) which catalyzes the condensation of dopamine and 4-hydroxyphenylacetaldehyde as the first step in benzylisoquinoline alkaloid biosynthesis.

RESULTS

With the availability of wild daffodil (Narcissus pseudonarcissus) database, a transcriptome-mining search was performed for NCS orthologs. A candidate gene sequence was identified and named norbelladine synthase (NBS). NpNBS encodes for a small protein of 19 kDa with an anticipated pI of 5.5. Phylogenetic analysis showed that NpNBS belongs to a unique clade of PR10/Bet v1 proteins and shared 41% amino acid identity to opium poppy NCS1. Expression of NpNBS cDNA in Escherichia coli produced a recombinant enzyme able to condense tyramine and 3,4-DHBA into norbelladine as determined by high-resolution tandem mass spectrometry.

CONCLUSIONS

Here, we describe a novel enzyme catalyzing the first committed step of AA biosynthesis, which will facilitate the establishment of metabolic engineering and synthetic biology platforms for the production of AAs.

Venous duplex scanning for unilateral symptoms: when do we need a contralateral evaluation?

OBJECTIVES

Determine the need for bilateral duplex scanning (DS) in patients with unilateral symptoms of acute DVT of the leg.

DESIGN

Prospective study.

MATERIALS

One thousand, one hundred and sixty-one consecutive patients with recent unilateral symptoms of pain or swelling.

METHODS

Bilateral DS were performed and demographic data including risk factors for DVT were entered into a computerised database.

RESULTS

Of the 250 cases (22%) of acute DVT, thrombus was confined to the symptomatic limb in 80% (200/250) and to the asymptomatic limb (AL) in 5% (12/250), while bilateral DVT was found in 15% (38/250). The management was not altered by the contralateral DS findings in any patient with bilateral thrombus. Ten of the 12 cases of DVT confined to the AL were localised to the infrapopliteal level; advanced malignancy, recent joint surgery or hypercoagulability were noted in nine patients, including all those requiring treatment.

CONCLUSIONS

In the presence of unilateral symptoms of DVT, we recommend DS of the symptomatic extremity only; bilateral examination should be confined to patients with normal duplex findings in the symptomatic limb following recent joint surgery, or in the presence of advanced malignancy or hypercoagulability. Bilateral DS would therefore be required in approximately 11% of cases with unilateral symptoms of DVT.

A prospective study comparing duplex scan and venography for diagnosis of lower-extremity deep vein thrombosis

This study was designed to compare duplex scanning with contrast venography for the diagnosis of acute deep vein thrombosis of the lower extremity, both at the femoropopliteal (above-knee) and tibioperoneal (below-knee) levels. A total of 216 patients with 220 limbs suspected of acute deep vein thrombosis underwent duplex scanning followed within 24 h by ascending venography. The two studies were interpreted independently by two physicians who were blinded to the results of the corresponding alternative study. Venography was positive for deep vein thrombosis in 44.5% of cases (98/220). Duplex scanning was inadequate at the above-knee level in two cases (0.9%) and at the below-knee level in 17 cases (7.7%). Sensitivity and specificity of duplex scanning at above-knee level were 98.7% and 100% respectively while corresponding values were 85.2% and 99.2% at below-knee level. By excluding technically inadequate duplex studies, the sensitivity at below-knee level was clearly improved (93.8%). It is concluded that with meticulous technique, duplex scanning is highly accurate in diagnosing acute deep vein thrombosis of symptomatic lower extremities, avoiding contrast venography in over 90% of the cases, even at the tibioperoneal level.