Molecular cloning, bacterial expression and promoter analysis of squalene synthase from Withania somnifera (L.) Dunal.

Withania somnifera (ashwagandha) is a rich repository of large number of pharmacologically active secondary metabolites known as withanolides. Though the plant has been well characterized in terms of phytochemical profiles as well as pharmaceutical activities, but there is sparse information about the genes responsible for biosynthesis of these compounds. In this study, we have cloned and characterized a gene encoding squalene synthase (EC 2.5.1.21) from a withaferin A rich variety of W. somnifera, a key enzyme in the biosynthesis of isoprenoids. Squalene synthase catalyses dimerization of two farnesyl diphosphate (FPP) molecules into squalene, a key precursor for sterols and triterpenes. A full-length cDNA consisting of 1765 bp was isolated and contained a 1236 bp open reading frame (ORF) encoding a polypeptide of 411 amino acids. Recombinant C-terminus truncated squalene synthase (WsSQS) was expressed in BL21 cells (Escherichia coli) with optimum expression induced with 1mM IPTG at 37°C after 1h. Quantitative RT-PCR analysis showed that squalene synthase (WsSQS) expressed in all tested tissues including roots, stem and leaves with the highest level of expression in leaves. The promoter region of WsSQS isolated by genome walking presented several cis-acting elements in the promoter region. Biosynthesis of withanolides was up-regulated by different signalling components including methyl-jasmonate, salicylic acid and 2, 4-D, which was consistent with the predicted results of WsSQS promoter region. This work is the first report of cloning and expression of squalene synthase from W. somnifera and will be useful to understand the regulatory role of squalene synthase in the biosynthesis of withanolides.

Bhat WW ，Lattoo SK ，Razdan S ，Dhar N ，Rana S ，Dhar RS ，Khan S ，Vishwakarma RA ... -  《-》

Molecular characterization and promoter analysis of squalene epoxidase gene from Withania somnifera (L.) Dunal.

Razdan S ，Bhat WW ，Rana S ，Dhar N ，Lattoo SK ，Dhar RS ，Vishwakarma RA ... -  《-》

Functional characterization and differential expression studies of squalene synthase from Withania somnifera.

Squalene synthase (SQS: EC 2.5.1.21) is a potential branch point regulatory enzyme and represents the first committed step to diverge the carbon flux from the main isoprenoid pathway towards sterol biosynthesis. In the present study, cloning and characterization of Withania somnifera squalene synthase (WsSQS) cDNA was investigated subsequently followed by its heterologous expression and preliminary enzyme activity. Two different types of WsSQS cDNA clones (WsSQS1and WsSQS2) were identified that contained an open reading frames of 1,236 and 1,242 bp encoding polypeptides of 412 and 414 amino acids respectively. Both WsSQS isoforms share 99 % similarity and identity with each other. WsSQS deduced amino acids sequences, when compared with SQS of other plant species, showed maximum similarity and identity with Capsicum annuum followed by Solanum tuberosum and Nicotiana tabacum. To obtain soluble recombinant enzymes, 24 hydrophobic amino acids were deleted from the carboxy terminus and expressed as 6X His-Tag fusion protein in Escherichia coli. Approximately 43 kDa recombinant protein was purified using Ni-NTA affinity chromatography and checked on SDS-PAGE. Preliminary activity of the purified enzymes was determined and the products were analyzed by gas chromatograph-mass spectrometer (GC-MS). Quantitative real-time PCR (qRT-PCR) analysis showed that WsSQS expresses more in young leaves than mature leaves, stem and root.

Gupta N ，Sharma P ，Santosh Kumar RJ ，Vishwakarma RK ，Khan BM ... -  《-》

Molecular cloning and characterization of the yew gene encoding squalene synthase from Taxus cuspidata.

Huang Z ，Jiang K ，Pi Y ，Hou R ，Liao Z ，Cao Y ，Han X ，Wang Q ，Sun X ，Tang K ... -  《journal of biochemistry and molecular biology》

Molecular cloning and promoter analysis of squalene synthase and squalene epoxidase genes from Betula platyphylla.

Zhang M ，Wang S ，Yin J ，Li C ，Zhan Y ，Xiao J ，Liang T ，Li X ... -  《-》