The invasive cell coat at the microsporidian Trachipleistophora hominis–host cell interface contains secreted hexokinases

Abstract

Microsporidia are obligate intracellular parasites causing significant disease in humans and economically important animals. In parallel to their extreme genetic reduction, Microsporidia have evolved novel mechanisms for exploiting host metabolism. A number of microsporidians confer secretion of otherwise cytosolic proteins by coding for signal peptides that direct entry into the endoplasmic reticulum. The human pathogen Trachipleistophora hominis encodes for four hexokinases, three of which have signal peptides at the N-terminus. Here, we localized hexokinase 2 and hexokinase 3 through developmental stages of T. hominis using light and electron microscopy. Both proteins were concentrated in an extracellular coat previously termed the plaque matrix (PQM). The PQM (containing hexokinases) was morphologically dynamic, infiltrating the host cytoplasm predominantly during replicative stages. Throughout development the PQM interacted closely with endoplasmic reticulum that was demonstrated to be active in membrane protein biosynthesis and export. The impact of hexokinase on the host metabolism was probed using the fluorescent analog of glucose, 2-NBDG, which displayed spatially restricted increases in signal intensity at the parasite/vacuole surface, coincident with hexokinase/PQM distribution. Gross metabolic aberrations, measured using metabolic profiling with the Seahorse XF Analyzer, were not detectable in mixed stage cocultures. Overall, these results highlight a role for the extended cell coat of T. hominis in host-parasite interactions, within which secreted hexokinases may work as part of a metabolic machine to increase glycolytic capacity or ATP generation close to the parasite surface.

Evolution of microsporidia: An extremely successful group of eukaryotic intracellular parasites

“…The most extensively studied microsporidia protein that directly interacts with hosts is hexokinase. Microsporidia hexokinases have gained a signal peptide and were experimentally shown to be secreted in several species [19,[44][45][46]. This enzyme potentially increases host metabolism to provide nutrients for the developing parasites, and consistent with this idea, knockdown of the enzyme reduces microsporidia proliferation [44].…”

Peer Review #4 of "A secretory hexokinase plays an active role in the proliferation of Nosema bombycis (v0.1)"

“…Manuscript to be reviewed localization inside host cells. The location of NbHK during the proliferation stage of N. bombycis infection implied it may play a role in regulating and controlling the host's energy metabolism (Ferguson & Lucocq 2018).. HK, with or without its signal peptide, and fused with DsRed was expressed in BmN cells, which showed a similar subcellular localization. The localization of eukaryotic expressed rHK revealed that the signal peptide could not lead the rHK to be secreted or to enter into nuclei of healthy BmN or Sf9-III.…”

“…The high transcription of NbHK and its importance function implied the glycolysis also play a key role during its intracellular stages, even microsporidia could steal ATP from host.HK is a control valve of glycolysis. The secretory HK of microsporidia turn up the valve of glycolysis and the tricarboxylic acid cycle, which is a clever strategy to steal energy from the host (Ferguson & Lucocq 2018).…”

A secretory hexokinase plays an active role in the proliferation of Nosema bombycis

“…NbHK was predicted to be a secretory protein with a signal peptide, suggesting its potential localization inside host cells. The location of NbHK during the proliferation stage of N. bombycis infection implied it may play a role in regulating and controlling the host’s energy metabolism ( Ferguson & Lucocq, 2018 ). HK, with or without its signal peptide, and fused with DsRed was expressed in BmN cells, which showed a similar subcellular localization.…”

“…The P. locustae HK was predicted to contain a signal peptide, and the indirect immunofluorescent assay (IFA) showed a nuclear localization in the host ( Senderskiy et al, 2014 ; Timofeev et al, 2017 ). Then, special secreting hexokinase function which work as a regulator to increase ATP generation to parasite surface, was explored in Trachipleistophora hominis ( Ferguson & Lucocq, 2018 ).…”