Stage-specific proteomic and phosphoproteomic remodeling in Theileria annulata.

Theileria annulata, an apicomplexan parasite, causes lymphoproliferative disease in cattle and threatens the bovine industry in tropical and subtropical regions. To clarify life-cycle mechanisms and parasite-host interactions, we conducted high-resolution Orbitrap proteomic and phosphoproteomic analyses of the schizont and piroplasm stages. In total, we confidently identified and quantified 2,093 proteins; among these, 459 proteins were observed in a phosphorylated state, comprising 5,069 distinct phosphorylation sites. Functional enrichment analysis of differentially abundant proteins indicated stage-associated remodeling of genetic information processing, carbohydrate, lipid, and amino-acid metabolism, and core cellular processes. Stage-associated proteins were linked to host-parasite interaction, mitochondrial function, and metabolic adaptation. Schizonts showed broader proteomic and phosphorylation profiles consistent with higher biosynthetic and energy demands. In contrast, piroplasms exhibited a more restricted proteomic profile associated with erythrocyte adaptation and invasion-related functions. Together, these stage-resolved datasets provide a reference for proteome and phosphoproteome remodeling across development and prioritize candidate stage-associated proteins and phosphosites for future functional validation.