There is still no report on the purification of full-length squalene synthase by Ni-NTA chromatography, and so the recombinant protein was purified by Q-Sepharose followed by phenyl superose

and was analysed by 10% SDS-PAGE (Fig. 3a). The recovery of the enzyme activity in the various steps of selleckchem its purification procedure is presented in Table 1. Uninduced culture and BL21 (DE3) E. coli cells transformed with the pET-28(a) vector without the SSN gene were used as control. The specificity of the protein was further validated by Western blot by probing it with His antibodies because the expressed protein has a His6-tag attached to its C-terminal. The His antibodies specifically binds with His-expressed protein in the total cell lysate, pellet, supernatant and partially purified samples, while no cross-reactivity was detected in negative controls, which confirms the expression of His-tag protein in samples (Fig. 3b). To demonstrate that the overexpressed recombinant LdSSN protein actually has SSN activity, the conventional radioactive assay was performed using purified recombinant LdSSN protein. The pH dependence, thermal

stability and effect of denaturants (urea and GdmCl) were studied on recombinant LdSSN protein. Similar to most other SSNs, LdSSN showed activity selleck chemical in alkaline pH (Belingheri et al., 1991; Shechter et al., 1992). The pH optimum for the LdSSN was observed as 7.4, which was in comparison with trypanosomal, rat and daffodil SSN (Belingheri et al., 1991; Shechter et al., 1992; Sealey-Cardona et al., 2007), but was slightly

higher than the value of 7.2 reported for the yeast enzyme (Zhang et al., 1993). Moreover, a plateau was observed in the region of pH 7–7.8. The enzyme retained >80% activity in the buffer range of MOPS NaOH (Fig. 4a). Thermal stability of SSN varies in different organisms. The temperature optimum may be as high as 60 °C in Thermosynechococcus elongatus BP-1 (Lee & Poulter, 2008) and as low as 37 °C in other organisms. LdSSN showed maximum activity at 37 °C, whereas it exhibited Fenbendazole 83% and 88% activity at a temperature of 30 and 45 °C. LdSSN was found to be temperature sensitive as compared with other SSN, as it loses 85% of its activity at 60 °C (Fig. 4b). The effect of denaturants (urea and GdmCl) on LdSSN was assessed by incubating the enzyme at different concentrations of denaturants. The enzyme lost 81% and 86% of its activity at a concentration of 2 M urea and 0.3 M GdmCl, respectively (Fig. 4c and d). The enzyme loses >50% activity at a concentration of 1 M urea and 0.2 M GdmCl. The activity of the protein is more sensitive towards GdmCl than that of urea; this might be due to the ability of GdmCl to disturb the electrostatic interactions. The loss of activity can be due to unfolding of the enzyme, or due to disruption of the active-site microenvironment in the presence of denaturant molecules or due to preferential binding of molecules on the surface of LdSSN.