Co-expression of the human HLA-B27 class I antigen and the E3/19K protien of adenovirus-2 in insect cells using a baculovirus vector

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Abstract
We have expressed the human MHC class I HLA-B27 antigen, human β2-microglobulin, and the E3/19K protein of adenovirus-2 In Spodoptera frugiperda Insect cells (Sf9) by using the Autographs californica nuclear polyhedrosis virus. All genes were Inserted under the strong polyhedrin promoter in the vector pVL941. The proteins were expressed at high levels, ranging from 1 to 8 mg protein per 3 × 109 cells. Both a full-length and a truncated form of HLA-B27 were expressed. The latter was terminated at the border of the membrane-spanning segment at the extracellular side of the membrane. The HLA-B27 antigens and the E3/19K protein showed considerable heterogeneity with respect to glycosylatlon. Only a small fraction of HLA-B27 was assembled (2-microglobulin. Nevertheless, we were able to find the heavy chain at the cell surface, and by co-Infection with the recombinant virus for β2-microglobulin we observed an increase In cell surface expression. The E3/19K protein of adenovirus-2 blocks cell surface expression of HLA class I antigens in human cells and has a similar effect in Insect cells. In contrast to β2-microglobulin it assembles efficiently to the heavy HLA-B27 chain, both the full-length and truncated forms. The E3/19K protein does not stimulate assembly of HLA-B27-β2-microglobulin. Due to these problems of assembly and the heterogeneity of glycosylation we predict that It will be difficult to use HLA antigens produced in insect cells for X-ray crystallographic studies.