Comparing the expression of human DNA topoisomerase I in KM71H and X33 strains of Pichia pastoris

Background: Human is an essential cellular enzyme that is found in all human cells. As this enzyme is upregulated in cancer cells exceedingly, it is used as a target for cancer chemotherapeutic drug development. As such, producing the in-house enzyme for the purpose to speed up the search for more cost-effective and target specific hTopoI inhibitors is warranted. This study aims to compare the optimised conditions for the expression of hTopoI in KM71H (MutS) and X33 (Mut+) strains of Pichia pastoris. P. pastoris transfected with an hTopoI recombinant vector was used for the optimization of a higher level of hTopoI expression. Results: In the process, fed-batch cultivation parameters that influence the expression of hTopoI, such as culture temperature, methanol induction and feeding strategy, were optimised in the transfected KM71H and X33 P. pastoris strains in a shake flask system. The cell density and total protein concentration (protein level) of transfected P. pastoris were compared to determine the optimum culture conditions for each transfected P. pastoris strain. A higher hTopoI level was observed in the transfected KM71H culture supernatant (2.26 ng/mL) when the culture was incubated in the optimum conditions. Conclusions: This study demonstrated that MutS strain (KM71H) expressed and secreted a higher level of hTopoI heterologous protein in the presence of methanol compared to the Mut+ strain; X33 (0.75 ng/mL). However, other aspects of optimization, such as pH, should also be considered in the future, to obtain the optimum expression level of hTopoI in P. pastoris.

Distribution of HCV genotypes in volunteer blood donors in Guangzhou / 南方医科大学学报

<p><b>OBJECTIVE</b>To determine the distribution of HCV genotypes among volunteer blood donors in Guangzhou.</p><p><b>METHODS</b>Six-nine HCV RNA-positive samples were collected from volunteer blood donors in Guangzhou. NS5B fragments of HCV were amplified followed by DNA sequencing and phylogenetic analysis.</p><p><b>RESULTS</b>HCV genotypes were determined for 67 samples. Among them, the subtypes 1b, 2a, 3a, 3b, 6a and 6n were detected at the frequencies of 37.31%, 4.48%, 7.46%, 4.48%, 44.78% and 1.49%, respectively.</p><p><b>CONCLUSION</b>HCV 1b and 6a are the most predominant two subtypes among volunteer blood donors in Guangzhou.</p>