Intracellular Localization of Non-Secreted Recombinant β-Trace Protein in Vesicle-Like Structures of Baculovirus-Infected Insect Cells

Abstract

The baculovirus expression vector system (BEVS) has become an important tool for the production of high levels of recombinant proteins within short time. It possesses the capability to ensure all co- and posttranslational modifications like glycosylation, phosphorylation, signal-peptide cleavage, cellular targeting, secretion etc. In spite of that it is widely known that during the expression of recombinant proteins by BEVS substantial amounts of these proteins are accumulated intracellularly even in the presence of correct secretion signals [1] suggesting a bottleneck in the secretion pathway using this expression system. Using β-Trace Protein (β-TP), a glycoprotein bearing two N-glycosylation sites at Asn ₂₉, and Asn ₅₆ as a model, this complex phenomenon was investigated by high level expression in infected High Five™ cells. SDS-PAGE/western blotting indicates that after 72 hours about 55 % of the produced recombinant β-TP is accumulated within these cells. In the present work intracellular β-TP has been localized in vesicle-like structures and the accumulation process was analyzed. Furthermore, the N-glycan structures of the intracellular β-TP have been investigated proving that the recombinant protein is localized in the endoplasmic reticulum and the cis-golgi network.