The gene encoding polyneuridine aldehyde esterase of monoterpenoid indole alkaloid biosynthesis in plants is an ortholog of the alpha/beta hydrolase super family

The biosynthesis of the anti-arrhythmic alkaloid ajmaline is catalysed by m ore than 10 specific enzymes. In this multistep process polyneuridine aldeh yde esterase (PNAE) catalyses a central reaction by transforming polyneurid ine aldehyde into epi-vellosimine, which is the immediate precursor for the synthesis of the ajmalane skeleton. PNAE was purified from cell suspension cultures of Rauvolfia serpentina. The N-terminal sequence and endoproteina se LysC fragments of the purified protein were used for primer design and f or the amplification of specific PCR products leading to the isolation of P NAE-encoding cDNA from a R. serpentina library. The PNAE cDNA was fused wit h a C-terminal His-tag, expressed in Escherichia coli and purified to homog eneity using Ni-affinity chromatography. The pure enzyme shows extraordinar y substrate specificity, completely different to other esterases. Sequence alignments indicate that PNAE is a new member of the alpha/beta hydrolase s uper family.