Purification, molecular characterization and ligand binding properties of the major donkey seminal plasma protein DSP-1.

The research article discusses the identification, extraction, and study of a main protein found in donkey’s seminal fluid termed Donkey Seminal Plasma protein-1 (DSP-1). This protein shares similarities with seminal plasma proteins of other mammals and physically interacts with specific components of cell membranes, suggesting a potential role in sperm function.

Molecular Identification of DSP-1

• In this study, a primary protein from the Fibronectin Type-II (FnII) family named Donkey Seminal Plasma protein-1 (DSP-1), was identified in the seminal plasma of a donkey.
• The compositional examination of DSP-1 by mass spectrometry disclosed its similarities to other mammalian seminal plasma proteins like bovine PDC-109 and equine HSP-1/2. This suggests that its formation and workings might be similar in other mammalian species too.

Analysis of DSP-1 Structure

• A Liquid Chromatography-Mass Spectrometry (LC-MS) analysis pointed out that this protein has variations in glycosylation (addition of sugar molecules) and includes multiple acetylations (the addition of an acetyl group).
• Thermal stability studies demonstrated that the protein loses its natural structure at approximately 43°C and that binding to phosphorylcholine (PrC) – a constituent of choline phospholipids – increases its temperature stability.

Ligand Binding Properties of DSP-1

• Experiments with fluorescence titrations expressed that DSP-1 can identify and attach to lyso-phosphatidylcholine (a type of lipid) with more than 100-fold higher affinity than PrC. This implies its high specificity for this particular lipid molecule.
• The DSP-1 was also found to bind with erythrocytes, serving as a model for cell membranes. The interaction resulted in the disturbance in the cell membrane. Since it specifically binds to choline phospholipids, this suggests its probable significance in the physiological functioning of the sperm plasma membrane.