In silico characterization of Ajmaline biosynthesis pathway genes in plants

Abstract

Alkaloids sourced from medicinally important plants have wide impact on human health and well-being. Ajmaline, a monoterpenoid indole alkaloid have divergent pharmacological applications and require large scale production. Rauvolfia serpentina (Apocynaceae) is an important source of ajmaline. Our present work encompasses computational phylogenetic approach towards understanding the ancestry and divergence of six of the most important enzymes of ajmaline biosynthetic pathway- Strictosidine synthase (STR1, EC 4.3.3.2), Strictosidine glucosidase (SGR1, EC 3.2.1.105), Polyneuridine aldehyde esterase (PNAE, EC 3.1.1.78), Vinorine synthase (ACT/VS, EC 2.3.1.160), Vinorine hydroxylase (CYP5437/VH, EC 1.14.13.75) and Acetylajmalan esterase (AAE, EC 3.1.1.80). The highly restricted distribution of the genes represents their conservative nature and other than the members of Apocynaceae the genes of Ajmaline biosynthesis were found to be distributed in Rubiaceae, Malvaceae, Solanaceae, Oleaceae, Gelsemiaceae, Fabaceae, Fragaceae etc. Identification of conserved domains of the enzymes were analysed based on the sequence homology of related plants. Amino acid sequences of STR1 showed highly variable N-terminal region in contrast to SGR1 and VH where the N-terminal sequence showed more conservation than C-terminal half. PNAE and VS showed high conservation throughout the sequence. Homology modeling and in silico structural analysis of the enzymes provide valuable insight for further structural and functional experimentation. The results reflected conservation of the core catalytic domain in all the six enzymes studied which is useful for structure-based evolution studies or for rational design and modulation of the enzyme's substrate specificity. Extensive literature survey resulted in identification of homologous genes of the aforementioned enzymes in Arabidopsis thaliana whose expressions at different stress conditions and developmental stages were investigated in publicly available microarray-based platform. The genes were found to be upregulated under different biotic and abiotic stresses. Also differential expression was detected at developmental stages.The data presented here will positively contribute towards deciphering the intricacies of reaction mechanism and steer bioengineering of alkaloid production to benefit mankind.