Cell-Free Expression of a Plant Membrane Protein BrPT2 From Boesenbergia Rotunda.

Prenylation of aromatic natural products by membrane-bound prenyltransferases (PTs) is an important biosynthesis step of many bioactive compounds. At present, only a few plant flavonoid-related PT genes have been functionally characterized, mainly due to the difficulties of expressing these membrane proteins. Rapid and effective methods to produce functional plant membrane proteins are thus indispensable. Here, we evaluated expression systems through cell-based and cell-free approaches to express Boesenbergia rotunda BrPT2 encoding a membrane-bound prenyltransferase. We attempted to express BrPT2 in Escherichia coli and tobacco plants but failed to detect this protein using the Western-blot technique, whereas an intact single band of 43 kDa was detected when BrPT2 was expressed using a cell-free protein synthesis system (PURE). Under in vitro enzymatic condition, the synthesized BrPT2 successfully catalyzed pinostrobin chalcone to pinostrobin. Molecular docking analysis showed that pinostrobin chalcone interacts with BrPT2 at two cavities: (1) the main binding site at the central cavity and (2) the allosteric binding site located away from the central cavity. Our findings suggest that cell-free protein synthesis could be an alternative for rapid production of valuable difficult-to-express membrane proteins.

Purification, biochemical characterization and antioxidant property of ZCPG, a cysteine protease from Zingiber montanum rhizome.

Zingiber montanum cysteine protease glycoprotein (ZCPG) was purified to homogeneity by DEAE- cellulose and Sephadex G50 resulting in sixteen fold purification and total activity of 39.4U/mg. ZCPG presented a prominent single peak in HPLC chromatogram with an estimated molecular weight of 48kDa on native PAGE. SDS-PAGE gave two subunits of ∼24.3 and ∼24.6kDa showing its heterodimeric form. Protein sequencing was studied by MALDI-TOF MS/MS. Isoelectrofocusing exhibited two isoforms with pI values of 4.8 and 5.1. Analysis of the total carbohydrate by GC-MS/MS showed the presence of glucose, mannose, fucose and xylose. The pH and temperature optimum were 9 and 60°C respectively while Km and Vmax values were 0.5±0.03µg and 13.73±2.07U/ml respectively. ZCPG was strongly inhibited by NEM indicating the cysteine-type. Substrates such as casein, azocasein, gelatin, BSA and haemoglobin showed high relative activity. Metal ions of CuCl2, CoCl2, HgCl2 and ZnCl2 showed partial inhibition at 1mM concentration. Furthermore, ZCPG exhibited promising antioxidant activity in biochemical systems as well as THP-1 cells. These findings suggested, ZCPG with significant antioxidant activity might have potential applications in therapeutic and food industry.

Fluorescence quenching, structural and unfolding studies of a purified cysteine protease, ZCPG from Zingiber montanum rhizome.

A first attempt was made to study the fluorescence quenching, structure and unfolding nature of the purified Zingiber montanum (J.Koenig) Link ex A.Dietr. cysteine protease glycoprotein (ZCPG). ATR-IR spectra showed the presences of amide groups along with carbohydrate stretch indicating the glycoprotein nature. UV-vis spectra determined the presences of peptide groups and aromatic sidechains of tyrosine, tryptophan and phenylalanine. Far UV-Circular Dichroism spectrum revealed that the secondary structure consists of 47.6% α-helix, 14.1% ß-sheet, 16.1% ß-turn, and 22.2% random coil. CD signals revealed pronounced structural stability until 70°C followed by a significant variation in the secondary structure content in the transition temperature between 80-90°C. ZCPG retained most of its secondary structure in the pH range of 3.0-10.0. The extrinsic study shows that at pH 2.0, ZCPG revealed characteristics of a molten globule-like state exhibiting strong ANS binding. The effect of GdnHCl on ZCPG evaluated by far-CD emission maximum and fluorescence emission revealed that the unfolding was incomplete determining the stability of the protein. The microenvironment of the tryptophan residues indicated the presence of relatively exposed single tryptophan residue (per monomer) with positively charged side chains.

A short-chain dehydrogenase involved in terpene metabolism from Zingiber zerumbet.

The rhizome oil of Zingiber zerumbet Smith contains an exceptionally high content of sesquiterpenoids with zerumbone, a predominating potential multi-anticancer agent. Biosynthetic pathways of zerumbone have been proposed, and two genes ZSS1 and CYP71BA1 that encode the enzymes catalyzing the first two steps have been cloned. In this paper, we isolated a cDNA clone (ZSD1) that encodes an alcohol dehydrogenase capable of catalyzing the final step of zerumbone biosynthesis. ZSD1 has an open reading frame of 804 bp that encodes a 267-residue enzyme with a calculated molecular mass of 28.7 kDa. After expression in Escherichia coli, the recombinant enzyme was found to catalyze 8-hydroxy-α-humulene into zerumbone. ZSD1 is a member of the short-chain dehydrogenase/reductase superfamily (SDR) and shares high identities with other plant SDRs involved in secondary metabolism, stress responses and phytosteroid biosynthesis. In contrast to the transcripts of ZSS1 and CYP71BA1, which are almost exclusively expressed in rhizomes, ZSD1 transcripts are detected in leaves, stems and rhizomes, suggesting that ZSD1 may also be involved in other biological processes. Consistent with its proposed flexible substrate-binding pocket, ZSD1 also converts borneol to camphor with K(m) and k(cat) values of 22.8 µm and 4.1 s(-1) , displaying its bisubstrate feature.