Abstract
Seminal plasma (SP) proteins support the survival of spermatozoa acting not only at the plasma membrane but also by inhibition of capacitation, resulting in higher fertilizing ability. Among SP proteins, BSP (binder of sperm) proteins are the most studied, since they may be useful for the improvement of semen diluents, storage and subsequent fertilization results. However, an updated and detailed phylogenetic analysis of the BSP protein superfamily has not been carried out with all the sequences described in the main databases. The update view shows for the first time an equally distributed number of sequences between the three families: BSP, and their homologs 1 (BSPH1) and 2 (BSPH2). The BSP family is divided in four subfamilies, BSP1 subfamily being the predominant, followed by subfamilies BSP3, BSP5 and BSP2. BSPH proteins were found among placental mammals (Eutheria) belonging to the orders Proboscidea, Primates, Lagomorpha, Rodentia, Chiroptera, Perissodactyla and Cetartiodactyla. However, BSPH2 proteins were also found in the Scandentia order and Metatheria clade. This phylogenetic analysis, when combined with a gene context analysis, showed a completely new evolutionary scenario for the BSP superfamily of proteins with three defined different gene patterns, one for BSPs, one for BSPH1/BSPH2/ELSPBP1 and another one for BSPH1/BSPH2 without ELSPBP1. In addition, the study has permitted to define concise conserved blocks for each family (BSP, BSPH1 and BSPH2), which could be used for a more reliable assignment for the incoming sequences, for data curation of current databases, and for cloning new BSPs, as the one described in this paper, ram seminal vesicle 20 kDa protein (RSVP20, Ovis aries BSP5b).
Highlights
Mammalian spermatozoa require extensive sperm plasma membrane remodelling during epididymal transit and in the female reproductive tract to acquire their ability to fertilize [1,2]
Of note are the only two equine sequences (Q70GG5 and F6XU34) found in the BSP2 subfamily (Fig 1, yellow green), which has evolved in parallel to the other two BSP1 sequences described in Equus caballus (Table 1, Fig 1)
The phylogenetic analysis described in the present report (Fig 1 and S1 Fig) shows an up-dated picture of known BSPs proteins (BSP, BSP homolog 1 (BSPH1) and BSPH2) in protein databases (UniProt, NCBI and Ensembl)
Summary
Mammalian spermatozoa require extensive sperm plasma membrane remodelling during epididymal transit (epididymal maturation) and in the female reproductive tract (capacitation) to acquire their ability to fertilize [1,2]. Seminal plasma (SP) proteins have been recently shown to participate actively in both processes, in the survival of the spermatozoa and inhibiting the capacitation This combined effect results in higher fertilizing ability [3]. The common characteristic of these BSP proteins is the presence of two fibronectin type II domains (FN2 domain), which confer them many binding properties, such as attachment to glycosaminoglycans [6,7,8], choline phospholipids [9], high and low-density lipoproteins [10,11] and gelatin [8,12]. Homologs of these proteins have been recently characterized in mouse and human [7,8], and named as mouse BSP homolog 1–3 (BSPH1-3) and human BSP homolog 1 (BSPH1)
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