Gene cloning and preliminary function study of protein tyrosine phosphatase from Nocardia seriolae

Nocardia seriolae is the main pathogen of fish nocardiosis, which is a chronic systemic granuloma disease of fish. A gene of protein tyrosine phosphatase (PTP) was found by analyzing the whole genome sequence of N. seriolae, and bioinformatics analysis showed that the PTP gene mayencode a secreted protein which could possibly target host cell mitochondria. In this study, the gene cloning, subcellular localization, over-expression and mitochondrial membrane potential detection were carried out. The results showed that the protein PTP was identified in the extracellular products of N. seriolae, which confirmed that PTP was a secreted protein. Subcellular localization of PTP-GFP fusion proteins were evenly distributed in the whole cell of FHM cells, and did not coincide with the distribution of mitochondria, which indicated that the protein PTP was not targeted at mitochondria. Typical apoptotic features, such as nuclear pyrosis and apoptotic bodies, were found when PTP protein was expressed in FHM cells by both subcellular localization and over-expression studies. The mitochondrial membrane potential was significantly damaged in FHM at 48h after the transfection of pcDNA-PTP, which confirmed that PTP was a bacterial protein which can likely induce cell apoptosis. The gene cloning and preliminary function study of PTP from N. seriolae have laid the foundation for further research on the gene and for promoting the understanding of the pathogenic mechanism of N. seriolae.