Heterologous Expression of Nosema Bombycis Hexokinase in the Baculovirus-Sf9 Insect Cell System Confirms Its Accumulation in the Host Nuclei and Secretion by the Microsporidian Parasite

Hexokinase is one of the most interesting proteins secreted by entomopathogenic microsporidia into an infected cell.Its accumulation in the insect host nuclei suggests that the hexose-phosphorylating enzyme may also be involved in the regulation of transcription of host genes.In this study, a hexokinase of microsporidia Nosema bombycis was expressed in Sf9 lepidopteran cells using the baculovirus system.In contrast to green fluorescence protein and gluten-hydrolyzing proteinase of Sunn pest Eurygaster integriceps, expressed as the control proteins, the microsporidian recombinant enzyme without N-terminal signal peptide was accumulating in the nuclei of insect cells during heterologous expression.This result one more time confirms the nuclear localization of hexokinases secreted by microsporidia into the insect host cells and suggests that a model used is a convenient one to study an impact of N. bombycis hexokinase on the lepidopteran cells.Surprisingly, despite the elimination of signal peptide, the parasite enzyme was effectively secreted into the culture medium by Sf9 cells.Previously, we expressed several secretory proteins with their own or baculoviral glycoprotein gp67 signal peptides, but none of them was secreted as effectively as N. bombycis hexokinase.This unexpected result raises the question about signal sequences and mechanisms of protein secretion in microsporidia.