Cloning of genes involved this website in PNP degradation Two positive clones (4-2 M and 4-8 G) were obtained by PCR-based screening of the genomic library of strain 1-7, and a 10.6 kb fragment in 4-2 M containing 11 complete ORFs (pdcABCDEFG, orf1, orf2, orf3, orf4) was cloned. Their annotations were determined from BLAST analysis, and the ORF organization is shown in Figure 4. Genes pdcABCDEFG showed a high similarity with the reported PNP degradation cluster (pnpABCDEFG) from Pseudomonas sp. strain WBC-3 , and the proteins PdcABCDEFG had no potential signal peptides as determined
by SignalP 3.0. Figure 4 Organization of the putative ORFs in Pseudomonas sp. 1-7. Organization of putative ORFs in the 10.6-kb DNA fragment. The arrows indicate the size and direction of each ORF. Expression and purification of PdcF, PdcG and PdcDE To characterize the enzymes involved in PNP degradation, four genes (pdcDEFG) were expressed in E. coli BL21 (DE3). After purification by Ni2+-NTA affinity chromatography, buy Adriamycin the proteins His6-PdcF, His6-PdcG, His 6-PdcD and His 6-PdcE had been purified to apparent homogeneity by SDS-PAGE analysis. Their molecular masses were 37 kDa, 52 kDa, 38 kDa and
18 kDa, respectively (Figure 5), being consistent with the calculated molecular masses of these proteins. Figure 5 SDS-PAGE of purified recombinant His 6 -PdcDE, His 6 -PdcF and His 6 -PdcG. Lane M: molecular mass standards (sizes in kDa are shown on the left); lane 1: purified His6-PdcDE; lane
2: purified His6-PdcF; lane 3: purified His6-PdcG. Enzymatic assays of HQ 1,2-dioxygenase activity HQ 1,2-dioxygenase, being the third enzyme of the HQ pathway, catalyzes the ring cleavage reaction of HQ to 4-HS . Two genes (pdcD and pdcE) were cloned into the expression vectors pET-30a and pET-2230, respectively, and PdcD and PdcE were co-expressed in E. coli BL21 (DE3) to allow endogenous assembly of the active HQ 1,2-dioxygenase. Spectrophotometric analysis of HQ 1,2-dioxygenase (His6-PdcDE) activity Cyclin-dependent kinase 3 showed a spectral change from 290 nm to 320 nm during the oxidation of HQ by His6-PdcDE (Figure 6b), there being no spectral changes in the negative controls (Figure 6a). These results indicated that His6-PdcDE catalyzed the ring cleavage reaction of HQ to 4-HS. Figure 6 Enzyme activity assay of PdcDE. (a) Absorbance readings from 250 nm to 320 nm in the absence of His6-PdcDE; (b) Spectral changes during rapid oxidation of HQ by purified His6-PdcDE. The spectra were recorded a total of five times over a five minute period (marked 1-5). The arrows indicate the direction of spectral changes. His6-PdcDE was active over a TGF-beta inhibitor temperature range of 20-70°C, with an optimal activity at 40°C, and from pH 3.0-10.0 with an optimum activity at pH 6.0 (Table 2, Additional file 1: Figure S3a, S3c). Further, the purified enzyme retained 35% activity after 20 min at 60°C, 20% activity after 30 min at pH 3.0 and 60% activity after 30 min at pH 10.