The baculovirus/insect cell system (Autographa and function of proteins. One post-translational modicalifornica multiple nuclear polyhedrosis virus/Spodopfication which is currently being studied is the attachtera frugiperda Sf9 cells) was used to express the GPIment of preassembled glycosylphosphatidylinositol anchored human melanoma tumor antigen, melanotrans-(GPI) anchors to proteins. This modification allows ferrin or p97. This system served to study the expression proteins to become plasma membrane associated and and productivity of recombinant GPI-anchored p97 by insect cells. The Sf9 cells expressed a cell surface GPI-confers on these proteins certain unique properties, such anchored form of p97 as well as a soluble form of p97 as apical localization in polarized cells and ability to that did not appear to be derived from the GPI-anchored interact with proteins involved in signal transduction form of p97. Both recombinant forms, although Endo H and cell protection resistant, migrated slightly faster (ศ88 kDa) than the na- . The basic GPI anchor tive p97 (ศ95-97 kDa). The insect GPI-anchored p97 was sensitive to PI-PLC, which exposed a detectable cross-structure of ethanolamine-PO 4 -(mannose) 3 -glycosreacting determinant. The Sf9 cell surface p97 expression amine-inositol-PO 4 -lipid has been found to be highly was similar to that of human melanoma (SK-MEL-28) conserved throughout eukaryotic evolution. Modificacells, whereas the Sf9 cell specific secretion rate was 10tions can be made to this structure by the addition of fold higher. Also Sf9 cells retained considerably higher various side chains, with the most elaborate side chains levels of p97 within the cell. The Sf9 cell surface expression of p97 varied with time after infection, with the maxi-being found in protozoa mum expression, which appeared independent of multi- . Alplicities of infection greater than 1, occurring at 48 h. After though the biosynthesis and function of GPI anchors 48 h, levels of cell surface and secreted p97 fell whereas have been extensively studied in mammalian cells and p97 retained within the cell increased, which possibly protozoa reflected the lytic nature of the expression system. The successful expression of GPI-anchored human p97 by the Low, 1989;, little attenbaculovirus/insect cell system not only provides a source tion has been paid to the expression of GPI anchors in of p97 for further research but also is the basis of an lower invertebrates such as insect cells.
alternative method for the commercial production of GPI-
The baculovirus/insect cell system has been used to anchored proteins.