Identification of a new subtilisin-like protease NbSLP2 interacting with cytoskeletal protein septin in Microsporidia Nosema bombycis

•A new subtilisin-like protease NbSLP2 with a transmembrane in Nosema bombycis was identified.•NbSLP2 was distributed around the spore wall in the germinated and ungerminated spores.•NbSLP2 was proved directly interacted with cytoskeletal protein Nbseptin2.

Nosema bombycis is the pathogen of pébrine which brings heavy losses to sericulture every year. As a member of serine proteases, subtilisin-like protease (SLP) is related to the pathogenicity in fungi. In this study, we characterized a novel 63.8 kDa subtilisin-like protease NbSLP2 with a predicted transmembrane domain from Microsporidia, N. bombycis. RT-PCR showed that the transcript of NbSLP2 was detected from third day post infection. Immunofluorescence assay (IFA) indicated that NbSLP2 mainly scattered around the spore wall of N. bombycis. Co-immunoprecipitation data and liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) analysis revealed that NbSLP2 directly interacts with septin2 of N. bombycis, which is a cytoskeletal protein. IFA showed that NbSLP2 and Nbseptin2 co-localized beneath the spore wall. NbSLP2 can be pulled down by Nbseptin2, further confirming the interaction between NbSLP2 and Nbseptin2. As an important serine protease with a transmembrane domain, NbSLP2 interacting with Nbseptin2, a scaffold protein adjacent to the membrane may provide advantages to stabilize the NbSLP2 for its hydrolysis function.

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