Isolation and characterization of an ovoinhibitor, a multidomain Kazal-like inhibitor from Turkey (Meleagris gallopavo) seminal plasma.

Turkey seminal plasma contains three serine proteinase inhibitors. Two of them, with low molecular masses (6 kDa), were identified as single-domain Kazal-type inhibitors responsible for regulating acrosin activity. Our experimental objective was to isolate and characterize the inhibitor with the high molecular weight from turkey seminal plasma. The inhibitor was purified using hydrophobic interaction and affinity chromatography. Pure preparations of the inhibitor were used for identification by mass spectrometry, for determination of physicochemical properties (molecular weight, pI, and content and composition of the carbohydrate component), for kinetic studies, and for antibacterial tests. Gene expression and immunohistochemical detection of the inhibitor were analyzed in the testis, epididymis, and ductus deferens. The inhibitor with a high molecular weight from turkey seminal plasma was identified as an ovoinhibitor, which was found in avian semen for the first time. The turkey seminal plasma ovoinhibitor was a six-tandem homologous Kazal-type domain serine proteinase inhibitor that targeted multiple proteases, including subtilisin, trypsin, and elastase, but not acrosin. Our results suggested that hepatocyte growth factor activator was a potential target proteinase for the ovoinhibitor in turkey seminal plasma. The presence of the ovoinhibitor within the turkey reproductive tract suggested that its role was to maintain a microenvironment for sperm in the epididymis and ductus deferens. The turkey seminal plasma ovoinhibitor appeared to play a significant role in an antibacterial semen defense against Bacillus subtilis and Staphylococcus aureus.