Yf. Zhang et al., EXPRESSION, CHARACTERIZATION, AND IMMUNOREACTIVITIES OF A SOLUBLE HEPATITIS-E VIRUS PUTATIVE CAPSID PROTEIN SPECIES EXPRESSED IN INSECT CELLS, Clinical and diagnostic laboratory immunology, 4(4), 1997, pp. 423-428
The hepatitis E virus (HEV) open reading frame-2 (ORF-2) is predicted
to encode a 71-kDa putative capsid protein involved in virus particle
formation. When insect Spodoptera frugiperda (Sf9) cells were infected
with a recombinant baculovirus containing the entire ORF-2 sequence,
two types of recombinant proteins were produced: an insoluble protein
of 73 kDa and a soluble protein of 62 kDa. The 62-kDa species was show
n to be a proteolytic cleavage product of the 73-kDa protein. N-termin
al sequence analysis of the 62-kDa protein indicated that it lacked th
e first 111 amino acids that are present in the full-length 73-kDa pro
tein. A soluble 62-kDa protein was produced without the proteolytic pr
ocessing by inserting the coding sequence of amino acids 112 to 660 of
ORF-2 in a baculovirus expression vector and using the corresponding
virus to infect Sf9 cells. The two recombinant 62-kDa proteins made by
different mechanisms displayed immunoreactivities very compatible to
each other. The 62-kDa proteins obtained by both proteolytic processin
g and reengineering demonstrated much higher sensitivities in detectin
g anti-HEV antibodies in human sera than the antigens made from bacter
ia, as measured by enzyme-linked immunosorbent assay. The data suggest
that the soluble 62-kDa protein made from insect cells contains addit
ional epitopes not present in recombinant proteins made from bacteria.
Therefore, the 62-kDa protein may be useful for HEV diagnostic improv
ement and vaccine development. The reengineered construct allows for t
he consistent large-scale production of the soluble 62-kDa protein wit
hout proteolytic processing.