ON PROTEINS OF THE MICROSPORIDIAN INVASIVE APPARATUS - COMPLETE SEQUENCE OF A POLAR TUBE PROTEIN OF ENCEPHALITOZOON-CUNICULI

The microsporidian Encephalitozoon cuniculi is an obligate intracellul ar 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 (PTP s) in E. cuniculi, a major PTP was isolated from two-dimensional gels and two peptide fragments were sequenced. The complete nucleotide sequ ence of the corresponding gene was obtained using a combination of PCR amplification and cloning techniques. The gene exists as a single cop y per haploid genome and encodes an acidic proline-rich protein, with a deduced molecular mass of 37 kDa, that contains four tandemly arrang ed 26-amino-acid repeats. An N-terminal region of 22 residues represen ts a cleaved signal peptide, probably involved in the targeting of the PTP, No similarity with known proteins has been found. The protein wa s expressed in Escherichia coli, purified and injected into mice. The antisera reacted specifically with the polar tube in indirect immunofl uorescence assays and electron microscope immunocytochemistry. Further identification of conserved and variable PTP structural motifs should be useful for diagnostic purposes and new therapeutic strategies.