AbstractThe DagA gene and DagA(▽), which is a DagA gene encoding sequence without signal peptide, were cloned from genome DNA ofPseudoalteromonas atlantica19262 by polymerase chain reaction (PCR). After ligation with pET21 vector, DagA and DagA(▽) were respectively expressed inEscherichia coliER2566 using molecular chaperones DsbC and FkpA. A strain of ER2566-pET21a-DagA(▽)-DsbC was screened as a highly effective expressing system in the form of an inclusion body that had the target protein with up to 60% total bacterial protein. DagA protein was renatured and purified by dissolving it in 8 mol/l of urea, using Ni-NTA resin affinity chromatography and refolding using the urea gradient method. DagA with a molecular weight of ~30.8 kDa was identified by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) and had the ability to digest agarose. In a pH range of 4.8–6.8, DagA maintained a bioactivity greater than 60%, with 5.8 being the optimum pH, and it exhibited activity at temperatures from 37°C to 60°C, with 55°C being the optimum temperature.

The coding region of dagA gene and dagA(▽) gene without signal peptide were cloned by PCR and the length were 873bp and 813bp respectively.The similarity between the coding region of dagA gene and Pseudomonas atlantica β-agaraseⅠdagA from NCBI is 99.8%,and of dagA(▽) is 100%.Both of the genes were co-expressed with molecular chaperones by construction of express vector of pET21a-dagA and pET21a-dagA(▽),transforming to different hosts which are BL21(DE3),Origami B(DE3)and ER2566.The recombinant strain of ER2566-pET21a-dagA(▽)-FkpA was isolated as a high effective secretory expression strain after analyzing the character and quantity of the expression realized by different E.coli expression systems through SDS-PAGE electrophoresis.

Fibrolase is a non-hemorrhagic zinc metalloproteinase isolated from southern copperhead snake venom (Agkistrodon contortrix contortrix) and is capable of degrading fibrin clots resulting from purified fibrinogen or from blood plasma. Alfimeprase, a truncated form of fibrolase, as a clinical agent was successfully completed PhaseII clinical trials.The cDNA of alfimeprase was amplified by recursive PCR, digested with BamHI and HindII, and cloned into pET43.1a, pMALp2X and pMALc2X vectors to generate fusions with NusA, MBP and sMBP(with signal peptide), respectively. Nus/alfimeprase was expressed in soluble form by co-expressing with chaperone FkpA and inducing with1mmol/L IPTG. The fusion protein accounted for about 25 % of total protein following cell lysis. Alfimeprase was successfully purifiesd by Ni-NTA affinity chromatography and cleaved by enterokinase. The results demonstrate the fibrinolytic activity of recombinant alfimeprase using fibrin plate assays and fibrinogen hydrolysis.