Supplementary MaterialsAdditional file 1: Figure S1. and characterized the first spore wall protein of EHP (EhSWP1). EhSWP1 contains three heparin binding motifs (HBMs) at its N-terminus and a Bin-amphiphysin-Rvs-2 (BAR2) domain at its C-terminus. A phylogenetic analysis revealed that EhSWP1 is similar to an uncharacterized spore wall protein from In a cohabitation bioassay using EHP-infected shrimp with na?ve shrimp, the expression of was detected by RT-PCR in the na?ve test shrimp at 20 days after the AVN-944 distributor start of cohabitation. Immunofluorescence analysis confirmed that EhSWP1 was localized in the walls of purified, mature spores. Subcellular localization by an immunoelectron assay revealed that EhSWP1 was distributed in both the endospore and exospore layers. An in vitro binding assay, a competition assay and mutagenesis studies revealed that EhSWP1 is a heparin binding protein. Conclusions Based on our results, we hypothesize that EhSWP1 is an important host-parasite interaction protein involved in tethering spores to host-cell-surface heparin during the process of infection. Electronic supplementary material The online version of this article (10.1186/s13071-018-2758-z) contains supplementary material, which is available to authorized users. in silkworms in the nineteenth century , it remains the cause of a fatal disease referred to as Pbrine that causes economic losses in the sericulture industry [5, 6]. (EHP) is a close evolutionarily relative of and other human-infecting microsporidia in the genus that cause life-threatening diarrhea in immunocompromized humans . In aquatic animals, infection of microsporidia in fish leads to reduction in growth rate and productivity , and this is true also for EHP in shrimp . Microsporidia display many unique cellular AVN-944 distributor and genetic characteristics. At the cellular level, microsporidia lack peroxisomes and a typical Golgi structure [10, 11]. Their mitochondria are structurally and functionally reduced into organelles called mitosomes [12, 13]. Their genomes are remarkably compact due to the loss of genes in metabolic pathways and reduction in intergenic spaces . The 2 2.3 Mbp genome AVN-944 distributor of is the smallest eukaryotic genome known AVN-944 distributor to date . In addition, microsporidia have developed a characteristic invasion mechanism that involves the polar tube and the spore wall . At the DPP4 first step of infection, the spore wall proteins are capable of interacting with host cell glycosaminoglycans (GAGs) [17, 18]. Under suitable conditions, the polar tube is extruded to pierce the host cell membrane. This process rapidly occurs in less than 2 milliseconds [11, 19]. The polar tube then serves as a conduit to transfer an infectious sporoplasm into the host cell to begin the parasitic, intracellular phase of the life-cycle . The spore walls of microsporidia consist of two layers, a proteinaceous electron dense exospore layer and a chitinous electron lucent endospore layer . Many spore wall proteins (SWPs) are found in these layers . They participate in the host cell recognition process and provide structural support for the spore wall [17, 21, 22]. SWPs have been extensively characterized for the genera and [22C27], EcEnP1, EcEnP2 and chitin deacetylase (EcCDA) from [28, 29], and EiEnP1 from . Recently, SWP2 (AlocSWP2) has been shown to be involved in sporulation . Hepatopancreatic microsporidiosis (HPM) in cultivated shrimp is characterized by slow growth and wide size variation, making the causative agent (EHP) an economically important pathogen for shrimp farmers [31, 32]. EHP was initially reported as a new, undescribed microsporidian in hepatopancreatic tissue of the black tiger shrimp in Thailand in 2004 , but it was not characterized and named as a new species until 2009 . Thus, it was an endemic pathogen that was also able to cause AVN-944 distributor disease in the exotic Pacific-white shrimp  that replaced as the dominant and most economically.