A comprehensive proteome and the first phosphoproteome reveal extensive phosphorylation of carbohydrate metabolism in Cryptosporidium parvum sporozoites

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Abstract
Background: Cryptosporidium parvum is an obligate apicomplexan parasite and a major cause of diarrheal disease in humans and animals worldwide. Despite its public health importance, the molecular regulation of parasite metabolism, particularly at the post-translational level, remains poorly understood. This study aims to understand major pathways regulated by protein phosphorylation in sporozoites, the parasite invasive stage, by comparative analysis of the proteomic and phosphoproteomic profiles. Methods: The proteome and phosphoproteome of excysted sporozoites of C. parvum were determined by data-independent acquisition-based mass spectrometry. Highly abundant pathways at proteomic and phosphoproteomic levels were identified by functional enrichment. A relative phosphorylation index (RPI) was developed for comparative assessment of phosphorylation propensity across proteins. Results: Proteomics identified 2,272 proteins in the sporozoites, representing 58% of the predicted parasite proteome. Phosphoproteomics identified 8,994 phosphorylation sites across 2,141 proteins; after intensity filtering, 833 phosphoproteins were retained for downstream analysis, representing 36.7% of the detected proteome. The correlations between transcript and protein abundances are weak. Proteins involved in carbohydrate metabolism, particularly glycolysis, are highly abundant in the proteome and phosphoproteome. Proteins in carbohydrate metabolism, signaling, cytoskeletal organization, and host–parasite interaction are selectively phosphorylated. In carbohydrate metabolism, starch degradative enzymes exhibit greater phosphorylation propensity than glycolytic and fermentative enzymes. Conclusions: The C. parvum sporozoites translate more than half of the protein-coding genes, in which one-third of the proteome is phosphorylated in varied degrees. In the highly active energy metabolism, starch degradation enzymes show greater phosphorylation propensity than core glycolytic and fermentative enzymes. This study reveals the first phosphoproteome and the largest proteome for C. parvum , providing a resource for further investigations of the functional regulation by protein phosphorylation.
Funding Information
  • National Key Research and Development Program of China (2022YFD1800200)

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