title: [Optimization of the expression of human DNA topoisomerase I in Pichia pastoris].
abstract: Human DNA Topoisomerase I (hTopo I) has been identified to be an efficient target of many effective antitumor drugs. Natural hTopo I is not convenient to be used in screening because of its low concentration in cells. In order to fast screen new anticancer drugs targeting at hTopo I from natural compounds in vitro, hTopo I gene open reading frame (ORF) has been successfully cloned and overexpressed in Pichia pastoris. Total RNA extracted from Hela cells was reversely transcripted to synthesize cDNA with the hTopo I specific antisense primer and the hTopo I ORF was synthesized by PCR. After digestion with EcoR I and Kpn I, the synthesized fragment was inserted into pPICZaA, gave rise to pPICZalpha-hTopoI. After digestion with Sac I, the lined pPICZalpha-hTopoI was transformed into Pichia pastoris strains (KM71, X33 and SMD1168) by electroporation and integrated into their genome. After screened on YPDS plates (containing 1000 ug/mL zeocin), the high-copy recombinant strains (KM-hTopoI, X33-hTopoI and SMD-hTopol) could overexpress recombinant hTopo I, which was fused to the alpha-factor secretion signal and could be secreted into the supernatant in the culture. alpha-factor could be cleaved from the expressed protein during secretion. A higher activity amount of the enzyme was secreted by the particular strain SMD-hTopoI because of its absence of proteimase A than by other strains which possess proteinase A activity. After optimizing the fermentation conditions, a relatively higher enzyme activity in the culture supernatant could be obtained when SMD-hTopoI was induced in BMMY (pH7.25) at 20 degrees C , with addition of 0.5% (V/V) methanol and 3% (V/V) nutrient liquid every 24h. The enzyme activity reached 43 000 u/mL, the yield reached 11 mg/L, achieving approximate 10% of total protein in the culture supernatant. SDS-PAGE and Western blot analyses showed that the mass of the recombinant hTopo I was 91 kD with no glycosylation.
authors.affiliation: Department of Biochemistry, School of Life Sciences, ZhongShan (Sun Yat-sen) University, GuangZhou 510275, China.
authors.forename: Guo-Wu
authors.initials: GW
authors.lastname: Yang
authors.forename: Bao-Hong
authors.initials: BH
authors.lastname: Yuan
authors.forename: Kwok-Ping
authors.initials: KP
authors.lastname: Ho
authors.forename: Xin
authors.initials: X
authors.lastname: Dai
authors.forename: Yong-Cheng
authors.initials: YC
authors.lastname: Lin
authors.forename: Shi-Ning
authors.initials: SN
authors.lastname: Zhou
mesh_terms: D004264:DNA Topoisomerases, Type I / Q000096:biosynthesis* / Q000235:genetics; D005285:Fermentation; D006801:Humans; D010843:Pichia / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000096:biosynthesis* / Q000235:genetics
chemical_list: D011994:Recombinant Proteins; D004264:DNA Topoisomerases, Type I