Identification and localization of polar tube proteins in the extruded polar tube of the microsporidian Anncaliia algerae

Abstract

Microsporidia are obligate intracellular parasites able to infect a wide range of hosts from invertebrates to vertebrates. The success of their invasion process is based on an original organelle, the polar tube, which is suddenly extruded from the spore to inoculate the sporoplasm into the host cytoplasm. The polar tube is mainly composed of proteins named polar tube proteins (PTPs). A comparative analysis allowed us to identify genes coding for 5 PTPs (PTP1 to PTP5) in the genome of the microsporidian Anncaliia algerae. While PTP1 and PTP2 are found on the whole polar tube, PTP3 is present in a large part of the extruded polar tube except at its end-terminal part. On the contrary, PTP4 is specifically detected at the end-terminal part of the polar tube. To complete PTPs repertoire, sequential sporal protein extractions were done with high concentration of reducing agents. In addition, a method to purify polar tubes was developed. Mass spectrometry analysis conducted on both samples led to the identification of a PTP3-like protein (PTP3b), and a new PTP (PTP7) only found at the extremity of the polar tube. The specific localization of PTPs asks the question of their roles in cell invasion processes used by A. algerae.

Ultrastructural insights into the microsporidian infection apparatus reveal the kinetics and morphological transitions of polar tube and cargo during host cell invasion

“…Among the 2 states, of note was an apparent inverse correlation between the PT diameter and the thickness of the tube wall, which is composed of a lipid bilayer (pink arrows, Figs 1 and S2 ), flanked by an outer protein layer (light blue and magenta arrows, Figs 1 and S2 ). These observations are also in line with previous reports of an outer proteinaceous layer in germinated PTs [ 29 , 36 , 37 ]. Membrane-less PTs were not observed, and the PT membrane appeared continuous in all raw tomograms (small discontinuities in the membrane auto-segmentation likely being the result of mis-annotation due to limited signal-to-noise ratio).…”

Functional annotation of a divergent genome using sequence and structure-based similarity

“…5 a). Proteins from these clades all localize to different parts of the microsporidian PT [ 27 , 85 – 87 ] or the spore wall [ 31 ]. PTP4 and PTP6 were shown to mediate host cell binding, while RBLL-1 from E. cuniculi , was shown to interact with the PT and spore wall [ 31 ].…”

Shrimp injection with dsRNA targeting the microsporidian EHP polar tube protein reduces internal and external parasite amplification

“…The polar tube is a supramolecular complex of different polar tube proteins. To date, seven polar tube proteins have been identified (PTP1–PTP7) 3 – 8 . Among them, PTP2 has been previously studied in various microsporidian species.…”