Abstract
Several studies exhibit the presence of Ricinus Communis Agglutinin I (RCA) binding glycocalyx in mammalian spermatozoa. However, the molecular characterization of RCA binding glycocalyx in sperm membranes and its mechanism of action are poorly understood. The objective of the study was to identify and to characterize RCA binding glycoprotein of the bovine sperm plasma membranes (PM). Lectin blots of caput and cauda sperm PM revealed a 38 kDa polypeptide exhibiting the highest affinity to RCA among the several major RCA binding polypeptides. The 38 kDa RCA binding polypeptide of cauda sperm PM was purified and exhibited a charge train of three distinct spots with isoelectric points (pH 5.3 and 5.8). Proteomic identification yielded ten peptides that matched the sequence of Testis Expressed 101 protein (TEX101). Western blots data revealed that bovine sperm TEX101 is present in both testicular and epididymal sperm PM fractions. The native TEX101 polypeptide contains ~17 kDa N-linked oligosaccharides and the polypeptide is anchored to sperm membrane via a glycosylphosphatidylinositol lipid linkage. Immunofluorescence staining of sperm with anti-TEX101 demonstrated that the polypeptide is localized at the head of cauda sperm. Our biochemical results provide evidence on the presence of TEX101 in bovine epididymal sperm plasma membranes and may have a potential role in sperm-egg interaction.
Highlights
Spermatozoa leave the testis as morphologically differentiated cells, but they require posttesticular maturation in the epididymis to develop forward both motility and fertilizing ability [1]
We identified a 38 kDa Ricinus Communis Agglutinin I (RCA) binding polypeptide present in both caput and cauda sperm plasma membrane fractions and proteomic identification revealed that the 38 kDa polypeptide is a Testis Expressed 101 protein (TEX101) (Bos Taurus)
This study reveals that the 38 kDa polypeptide exhibits the highest affinity to RCA among the several major RCA binding polypeptides both in caput and cauda sperm plasma membrane fractions
Summary
Spermatozoa leave the testis as morphologically differentiated cells, but they require posttesticular maturation in the epididymis to develop forward both motility and fertilizing ability [1]. A hallmark feature of the mammalian spermatozoon is its highly polarized architecture, which is exhibited both in the restricted distribution of specific organelles and in the partitioning of its plasma membrane into domains of distinct composition and function [1, 8, 9]. The importance of this polarity is emphasized during discrete fertilization steps, which require the participation of selected organelles and membrane domains. We identified a 38 kDa RCA binding polypeptide present in both caput and cauda sperm plasma membrane fractions and proteomic identification revealed that the 38 kDa polypeptide is a Testis Expressed 101 protein (TEX101) (Bos Taurus). We propose that the TEX101 polypeptide may play an important role in sperm-egg interaction
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