Extracellular proteins from Perkinsus olseni: LC-MS/MS-based proteomic profiling and functional insights into host-parasite interactions.

Perkinsus olseni is a protozoan parasite that causes significant economic losses in molluscan aquaculture due to perkinsosis in clams and oysters. However, the molecular mechanisms underlying its pathogenicity are still poorly understood. In this study, we performed high-resolution liquid chromatography-tandem mass spectrometry (LC-MS/MS) combined with integrative bioinformatics to generate the first comprehensive profile of the P. olseni extracellular proteome ("secretome"). A total of 619 proteins were identified, with functional annotations revealing a diverse secretome involved in multiple biological roles. Gene Ontology (GO) enrichment analysis showed significant representation across metabolic processes, stress response, and immune modulation. Among these, 373 well-characterized proteins were enriched in 16 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, grouped into six functional categories: antigen processing and presentation, pattern recognition receptor signaling, inflammatory pathways, endo-lysosomal and autophagic pathways, protein processing and export, and pathogen-pathogen interactions. Representative proteins linked to these pathways include bromo domain-containing proteins (BiP5), heat shock protein 90 (HSP90), EF-hand domain-containing protein (EFCH1), calcineurin (CaN), β-N-acetylhexosaminidase (HEXB), 14-3-3 protein 7 (TFT7), Rab GTPases (Rab1A, Rab11A), and vacuolar protein sorting-associated proteins (VPS11). Proteins associated with pathogen-pathogen interactions overlapped with bacterial, viral, and plant-pathogen pathways, suggesting cross-kingdom mimicry or facilitation of co-infections. Additionally, Glyceraldehyde-3-phosphate dehydrogenase (GAPDH), U2 small nuclear RNA auxiliary factor 1 like 4 (U2AF1L4), and 14-3-3 protein 7 (TFT7) were implicated in immune modulation and host interaction. These findings may inform future research on parasite-host interactions and provide new insights into the virulence strategies of P. olseni and identify potential molecular targets for controlling perkinsosis in aquaculture systems.