STUDIES ON EXPRESSION AND BIOCHEMICAL CHARACTERISTICS OF SINGLE CHAIN FRAGMENT VARIABLE A1 AGAINST WHITE SPOT SYNDROME VIRUS OF SHRIMP

White Spot Syndrome Virus (WSSV)was first found in Taiwan in 1992.And since 1993,white spot syndrome disease of Shrimps caused by this virus was widely spread throughout China,Asia and pan-Pacific Ocean.It's a great harm to the aquaculture of shrimps.Electron microscopy studies show that the WSSV virion is an ellipsoid to bacilliform,enveloped,particle with a tail-like appendage at one end. The virion contains a rod-shaped nucleocapsid,typically measuring 275nm in length and 120nm in width.The WSSV virion has a large circular double-stranded DNA of about 290-305 kb.The International Committee on Taxonomy of Viruses approved a proposal to erect WSSV as the type species of the genus Whispovirus,family Nimaviridae(www.ncbi.nlm.nih.gov/ICTVdb/Ictv/index.htm).Our laboratory has constructed an antibody phage display library against WSSV.After four rounds of panning against WSSV,192 out of 480 clones displayed WSSV binding activity.One of the positive clones,designated A1,had relatively higher activity specifically binding to WSSV.In this study,we has prepared soluble scFv A1 and purified it.After induced to express at 30℃ for 20h,the amount of this antibody can reach to 3.67%of total proteins in the bacteria.Using affinity chromatography column and Sephadex G-100 column,scFv A1 can be purified to be a single band in the SDS-PAGE.Its molecular weight is about 31.5 KD.Using isoelectrofocusing electrophoresis,the isoelectric point of scFv A1 was determined to be pH 5.8.The tests of ELISA indicate that lyophilized scFv A1 stored at room temperature for 4 years still kept high activity to bind to WSSV.