On proteins of the microsporidian invasive apparatus: complete sequence of a polar tube protein of Encephalitozoon cuniculi

Abstract

SummaryThe microsporidian Encephalitozoon cuniculi is an obligate intracellular parasite that can cause opportunistic infections in AIDS patients. Spore invasion of host cells involves extrusion of a polar tube. After immunocytochemical identification of several polar tube proteins (PTPs) in E. cuniculi, a major PTP was isolated from two-dimensional gels and two peptide fragments were sequenced. The complete nucleotide sequence of the corresponding gene was obtained using a combination of PCR amplification and cloning techniques. The gene exists as a single copy per haploid genome and encodes an acidic proline-rich protein, with a deduced molecular mass of 37 kDa, that contains four tandemly arranged 26-amino-acid repeats. An N-terminal region of 22 residues represents a cleaved signal peptide, probably involved in the targeting of the PTP. No similarity with known proteins has been found. The protein was expressed in Escherichia coli, purified and injected into mice. The antisera reacted specifically with the polar tube in indirect immunofluorescence assays and electron microscope immunocytochemistry. Further identification of conserved and variable PTP structural motifs should be useful for diagnostic purposes and new therapeutic strategies.

The microsporidian polar tube: A highly specialised invasion organelle

“…The E. cuniculi, E. hellem and E. intestinalis ptp1 have been cloned and the corresponding protein (PTP1) expressed in vitro for E. cuniculi and E. hellem (Delbac et al, 1998b. Clones have also been obtained for the ptp1 of several different isolates of E. hellem as well as G. americanus and B. algerae (Peuvel et al, 2000;Weiss, 2001;Xiao et al, 2001;Haro et al, 2003;Weiss L.M., unpublished data).…”

“…Clones have also been obtained for the ptp1 of several different isolates of E. hellem as well as G. americanus and B. algerae (Peuvel et al, 2000;Weiss, 2001;Xiao et al, 2001;Haro et al, 2003;Weiss L.M., unpublished data). The E. hellem ptp1 is 1362 bp and encodes a protein of 453 amino acids with a predicted molecular mass of 43 kDa while the ptp1 of E. cuniculi is 1188 bp and encodes a protein of 395 amino acids with a predicted molecular mass of 37 kDa (Delbac et al, 1998b;. These two microsporidia are in the same genus (Encephalitozoon) and cannot be distinguished ultrastructurally, their native PTP1s have similarities in overall amino acid composition, hydrophobicity, mass and immunologic epitopes, and their polar tubes have functional identity (Weiss, 2001).…”

Analogs of the Golgi complex in microsporidia: structure and avesicular mechanisms of function

“…This cellular model demonstrates a range of the important advantages: (1) During sporogony, these cells appear to intensively synthesize sporewall and polar-tube proteins in the ER and transport them to the forming structures. The N-terminal regions of the microsporidia spore-wall and polar-tube proteins contain signal peptides for ER translocation ( Delbac et al, 1998;Keohane and Weiss, 1999;Bohne et al, 2000;Hayman et al, 2001). (2) According to data from the genome project of the human microsporidia E. cuniculi (Katinka et al, 2001), as with all other eukaryotes, these cells possess all of the most important and well-characterized protein machineries that are involved in co-translational translocation of polypeptide chains into the ER lumen, as well as in their intracellular transport, although some of these lack non-essential components.…”

Genotyping Encephalitozoon cuniculi by Multilocus Analyses of Genes with Repetitive Sequences

“…This will allow the genotyping of E. cuniculi in large numbers of laboratories and better characterization of the epidemiology of human E. cuniculi infection. Recently, genes coding for the polar tube protein (PTP) and spore wall protein I (SWP-1) of E. cuniculi were reported (2,5). Because the gene has long central repeats of 78 bp in PTP and 15 and 36 bp in SWP-1 and the number of repeats in repetitive proteins tends to vary in other parasites such as Plasmodium spp., we examined the sequence diversity of PTP and SWP-1 genes among various isolates of E. cuniculi.…”