Comparative Analysis of the Proteins with Tandem Repeats from 8 Microsporidia and Characterization of a Novel Endospore Wall Protein Colocalizing with Polar Tube from Nosema bombycis

As a common feature of eukaryotic proteins, tandem amino acid repeat has been studied extensively in both animal and plant proteins. Here, a comparative analysis focusing on the proteins having tandem repeats was conducted in eight microsporidia, including four mammal‐infecting microsporidia (Encephalitozoon cuniculi, Encephalitozoon intestinalis, Encephalitozoon hellem and Encephalitozoon bieneusi) and four insect‐infecting microsporidia (Nosema apis, Nosema ceranae, Vavraia culicis and Nosema bombycis). We found that the proteins with tandem repeats were abundant in these species. The quantity of these proteins in insect‐infecting microsporidia was larger than that of mammal‐infecting microsporidia. Additionally, the hydrophilic residues were overrepresented in the tandem repeats of these eight microsporidian proteins and the amino acids residues in these tandem repeat sequences tend to be encoded by GC‐rich codons. The tandem repeat position within proteins of insect‐infecting microsporidia was randomly distributed, whereas the tandem repeats within proteins of mammal‐infecting microsporidia rarely tend to be present in the N terminal regions, when compared with those present in the C terminal and middle regions. Finally, a hypothetical protein EOB14572 possessing four tandem repeats was successfully characterized as a novel endospore wall protein, which colocalized with polar tube of N. bombycis. Our study provided useful insight for the study of the proteins with tandem repeats in N. bombycis, but also further enriched the spore wall components of this obligate unicellular eukaryotic parasite.