Identification of estrogen-responsive vitelline envelope protein fragments from rainbow trout (Oncorhynchus mykiss) plasma using mass spectrometry

Plasma peptides previously associated with exposure of juvenile male rainbow trout (Oncorhynchus mykiss) to the hormone 17β-estradiol (E2) were identified using matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF-MS). Specifically, plasma peptides of interest were fractionated and subsequently identified via spectra obtained by MALDI QqTOF MS/MS and LC-MALDI TOFTOF MS/MS analysis, de novo sequencing and database matching. The two peptide masses were identified as significant matches for fragments of the C-terminal propeptides from rainbow trout vitelline envelope protein (VEP)α and VEPγ isoforms. Our findings document the presence of the C-terminal propeptides from rainbow trout VEPα and VEPγ proteins in the bloodstream of juvenile male rainbow trout exposed to E2 via MALDI-TOF-MS detection. We provide three possible explanations for the presence of C-terminal propeptides in the bloodstream, as well as compare previously obtained hepatic transcriptomic results with the plasma proteomic results obtained in the present study.