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    • The Ala to Leu substitution would reduce the size

    2021-09-08

    The Ala116 to Leu110 substitution would reduce the size of the active-site cavity disfavoring the production of longer allylic compounds as a result of steric hindrance, according to the observations of Poulter and co-workers [29], [30]. However, this explanation appears to be unlikely since several other FPPSs also have a Leu or a similar residue (Ile, Met) at this position (Fig. 5). Thus, the most striking singularity in the residues lining the active site of the aphid enzyme appears to be the Gln107 at the C position, a substitution that represents a slight decrease in steric hindrance relative to the aromatic residue typically found at this position, but a change in the nature of the residue’s side chain (polar instead of hydrophobic). This modification could account for the observed aphid product distribution according to two complementary hypotheses. First, the presence of a Gln residue at this position would generate unfavorable interactions between the polar side-chain of the residue and the end of the GPP/FPP hydrophobic allylic chain of the product [31]. As a result shorter products would be favored. Second, chain GW788388 in the active site would require the disruption of hydrogen bonds between the Gln107 amide group and the neighboring residues which would favor the production of products with shorter allylic chains.
    Acknowledgements
    Introduction Hevea brasiliensis (Muell.) Arg., also known as Para rubber tree, is a perennial tree crop which is the principal commercial source for natural rubber (NR) production. Rubber trees start producing latex GW788388 after attaining 5–6years immaturity period and have a latex productive lifespan of 25–30years. It is reported that the global production of NR reached nearly 11milliontons in 2011 with Asia accounting for about 93% of the supply (Rahman et al., 2013). However, the demand for rubber (natural and synthetic) has steadily increased now and is expected to continue to increase in the years to come. Evans (2011) pointed out that in 2010 the consumption of natural rubber was 10.7milliontons for all rubber industry (tire and non-tire) which is predicted to rise to 15.4milliontons by 2020. Also the natural rubber will continue to play key roles in rubber product based industries across the world. H. brasiliensis, a tropical tree originating from South America, is widely cultivated in South America, Africa and South East Asia for the production of natural rubber (cis-1,4-polyisoprene) which is a mixture of high molecular weight polymers present in the latex. Among more than 2000 plant species known to produce natural rubber, the Brazilian rubber tree (H. brasiliensis) is the only commercial source at present (Venkatachalam et al., 2009). Due to the depletion in reserve fossil fuel for synthetic rubber, nowadays a great preference is provided by consumer for natural rubber production. Furthermore, to meet the anticipated demand for enhanced production of latex yield could depend on the available new rubber clones that are addressing various threats to rubber cultivation including long immaturity and low yield (Nugawela and Jom, 2011). Improvement of various tree species including rubber tree by conventional breeding is hindered by their long gestation periods, loss of desired genetic recombination, and occurrence of high degree of heterozygosity due to cross pollination. Biotechnological tools such as genetic transformation offer an attractive supplement to the conventional crop breeding program, because it provides the potential to rapid transfer of desirable genes for specific traits into selected clones without affecting their desirable genetic background (Jayashree et al., 2003). Therefore, isolation and cloning of key rubber biosynthetic genes are one of the prerequisites to develop genetically engineered rubber tree clones with enhanced latex production. A series of efforts has been made to isolate and characterize key genes or enzymes involved in rubber biosynthesis in H. brasiliensis (Attanyaka et al., 1991, Goyvaerts et al., 1991, Adiwilaga and Kush, 1996, Oh et al., 1999, Priya et al., 2006, Priya et al., 2007). However, the function and role of the proteins suggested to be involved in rubber biosynthesis in these reports remain to be verified. Rubber is biosynthesized by the sequential condensation of isopentenyl diphosphate (IDP) to the initiating allylic diphosphates such as geranyl diphosphate, farnesyl diphosphate (FDP), and geranylgeranyl diphosphate. farnesyl diphosphate synthase enzyme catalyzes 1'4 condensation of the 5-carbon isoprenoid compounds isopentenyl diphosphate (IPP) and 10-carbon geranyl diphosphate (GPP) to form the 15-carbon product farnesyl diphosphate (FPP).