Characterization of rubber particles and rubber chain elongation in Taraxacum koksaghyz

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Authors: Thomas Schmidt, Malte Lenders, Andrea Hillebrand, Nicole van Deenen, Oliver Munt and Rudolf Reichelt
Date: Feb. 19, 2010
From: BMC Biochemistry(Vol. 11)
Publisher: BioMed Central Ltd.
Document Type: Report
Length: 6,275 words

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Authors: Thomas Schmidt (equal contributor) [1]; Malte Lenders (equal contributor) [1]; Andrea Hillebrand [1]; Nicole van Deenen [1]; Oliver Munt [1]; Rudolf Reichelt [2]; Wolfgang Eisenreich [3]; Rainer Fischer [4]; Dirk Prüfer [1,4]; Christian Schulze Gronover (corresponding author) [4]

Background

Natural rubber poly(cis -1,4-isoprene) with a molecular mass of 10-10,000 kDa is one of the most important industrial raw materials in the world, and its sole commercial source is currently the para rubber tree Hevea brasiliensis [1]. Other sources, such as Russian dandelion (Taraxacum koksaghyz Rodin) and Guayule (Parthenium argentatum ), could be useful in the event of supply shortages as well as providing a suitable alternative for people with allergies to hevein, a major allergen present in H. brasiliensis latex [2, 3].

The biosynthesis of natural rubber takes place in the latex of laticifers or specialized parenchyma cells in the bark [1], where it is stored in rubber particles as an end product. Ultrastructural analysis of rubber particles from different species [4, 5, 6] revealed an almost identical globular structure that contains a homogeneous hydrophobic rubber core surrounded by an intact monolayer membrane. The monolayer membrane includes a mixture of lipids, proteins and other molecules with the hydrophilic portions of the phospholipids and glycosylated particle-bound proteins facing the cytoplasm [6, 7, 8, 9, 10]. The size of rubber particles ranges from 0.08-2 [mu]m in H. brasiliensis , 0.2-6.5 [mu]m in Ficus species and 1-2 [mu]m in P. argentatum [6, 11].

Natural rubber is synthesized by adding activated 2-methyl-1,3-butadiene (isopentenyl diphosphate, IPP) to the growing chain [12, 13]. This reaction is catalyzed by specific long-chain cis -prenyltransferases (CPTs, EC 2.5.1.20), which are probably located on the surface of rubber particles. According to their function, CPTs are classified as short-, medium- or long-chain polymerizing enzymes and can be distinguished from trans -prenyltransferases (TPTs) by the presence of five conserved protein motifs [14]. They are found in bacteria [15], yeast [16], animals including humans [17] and plants [18, 19, 20, 21, 22].

Recently, two CPTs (RER2 and SRT1) were isolated from Saccharomyces cerevisiae and were shown to be responsible for the biosynthesis of dolichol, a long-chain polyprenol with a saturated alpha-isoprene unit, which serves as a glycosyl carrier for protein glycosylation in the endoplasmic reticulum [23]. The first plant CPT was identified in Arabidopsis thaliana (ACPT), and appears to be required for normal growth and development [24]. The latex of H. brasiliensis contains at least two CPTs, designated HRT1 and HRT2 (for Hevea rubber transferase). The addition of recombinant HRT2 to washed latex particles supplemented with radioactively-labeled IPP resulted in the significant production of a high-molecular-weight labeled rubber product, whereas recombinant HRT1 showed no significant activity [25]. In vitro , initiation of rubber biosynthesis by HRT requires intact particles, isopentenyl diphosphate (IPP), allylic diphosphates such as farnesyl diphosphate (FPP) and divalent metal cations (Mg2+ or Mn2+ ) as a co-factor [26, 27, 28]. However, all attempts to purify a functional rubber transferase from rubber particles have failed, suggesting that the native enzyme needs additional factors for...

Source Citation

Source Citation
Schmidt, Thomas, et al. "Characterization of rubber particles and rubber chain elongation in Taraxacum koksaghyz." BMC Biochemistry, vol. 11, 2010, p. 11. Accessed 26 Sept. 2020.
  

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