A Straightforward Experimental Approach to Expression, Purification, Refolding, and Enzymatic Analysis of Recombinant Dengue Virus NS2B(H)-NS3pro Protease

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M. Junaid^1,2, C. Angsuthanasombat², J. E. S. Wikberg³, N. Ali⁴, and G. Katzenmeier^2*

¹Department of Pharmacy, University of Malakand, Chakdara, 18550 Pakistan; fax: +92-9467-6349; E-mail: juniphdr@gmail.com

²Laboratory of Molecular and Cellular Microbiology, Institute of Molecular Biosciences, Mahidol University, Salaya, 73170 Thailand; fax: +662-441-9906; E-mail: katzenmeier.ger@mahidol.ac.th; chanan.ang@mahidol.ac.th

³Division of Pharmacology, Department of Pharmaceutical Biosciences, Uppsala University, 75124 Sweden; fax: +46-1855-9718; E-mail: jarl.wikberg@farmbio.uu.se

⁴Department of Pharmacology, Institute of Basic Medical Sciences, Khyber Medical University, Peshawar, Khyber Pakhtunkhwa, 25000 Pakistan; fax: +92-9192-17704; E-mail: niazpharmacist@yahoo.com

^* To whom correspondence should be addressed.

Received February 14, 2013; Revision received April 23, 2013

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Dengue virus threatens around 2.5 billion people worldwide; about 50 million become infected every year, and yet no vaccine or drug is available for prevention and/or treatment. The flaviviral NS2B-NS3pro complex is indispensable for flaviviral replication and is considered to be an important drug target. The aim of this study was to develop a simple and generally applicable experimental strategy to construct, purify, and assay a highly active recombinant NS2B(H)-NS3pro complex that would be useful for high-throughput screening of potential inhibitors. The sequence of NS2B(H)-NS3pro was generated by overlap extension PCR (SOE-PCR) and cloned into the pTrcHisA vector. Hexahistidine-tagged NS2B(H)-NS3pro complex was expressed in E. coli predominantly as insoluble protein and purified to >95% purity by single-step immobilized metal affinity chromatography. SDS-PAGE followed by immunoblotting of the purified enzyme demonstrated the presence of the NS2B(H)-NS3pro precursor and its autocleavage products, NS3pro and NS2B(H), as 37, 21, and 10 kDa bands, respectively. Kinetic parameters, K_m, k_cat, and k_cat/K_m for the fluorophore-linked protease model substrate Ac-nKRR-amc were obtained using inner-filter effect correction. The kinetic parameters K_m, k_cat, and k_cat/K_m for Ac-nKRR-amc substrate were 100 µM, 0.112 s^–1, and 1120 M^–1·s^–1, respectively. A simplified procedure for the cloning, overexpression, and purification of the NS2B(H)-NS3pro complex was applied, and a highly active recombinant NS2B(H)-NS3pro complex was obtained that could be useful for the design of high-throughput assays aimed at flaviviral inhibitor discovery.

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KEY WORDS: Dengue virus, NS2B(H)-NS3pro protease, purification, assay, substrate

DOI: 10.1134/S0006297913080099

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