Temperature dependent characteristics of a recombinant infectious hematopoietic necrosis virus glycoprotein produced in insect cells

A recombinant infectious hematopoietic necrosis virus (IHNV) glycoprotein (G protein) was produced in insect cells using a baculovirus vector (Autographa californica nuclear polyhedrosis virus). Characteristics of this protein were evaluated in relation to native viral G protein. A full-length (1.6 kb) cDNA copy of the glycoprotein gene of IHNV was inserted into the baculovirus vector under control of the polyhedrin promoter. High levels of G protein (approximately 0.5 mu g/1 x 10(5) cells) were produced in Spodoptera frugiperda (Sf9) cells following recombinant baculovirus infection. Analysis of cell lysates by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and Western blot revealed a recombinant IHNV G of slightly higher mobility on the gel than the viral G protein. Differences in mobility were abrogated by endoglycosidase treatment. When the recombinant G protein was produced in insect cells at 20 degrees C (RecG(low)), immunostaining and cell fusion activity demonstrated surface localization of the protein. In contrast, when recombinant protein was produced at 27 degrees C (RecG(high)), G protein was sequestered within the cell, suggesting that at the 2 different temperatures processing differences may exist. Eleven monoclonal antibodies (MAbs) were tested by immunoblotting for reactivity to the recombinant G protein. All 11 MAbs reacted to the reduced proteins. Four MAbs recognized both RecG(high) and RecG(low) under non-reducing conditions; however, 1 neutralizing MAb (92A) recognized RecG(low) but failed to react to RecG(high) under non-reducing conditions. This suggests that differences exist between RecG(low) and RecG(high) which may have implications in the development of a properly folded recombinant G protein with the ability to elicit protective immunity in fish.