Spermadhesins: A new protein family. Facts, hypotheses and perspectives

Summary Spermadhesins are a novel family of secretory proteins expressed in the male genital tract of pig, horse and bull. They are major products of the seminal plasma and have been found to be peripherally associated to the sperm surface. The structure and function of spermadhesins have been thoro...

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Bibliographic Details
Published in:Andrologia 1998-08, Vol.30 (4-5), p.217-224
Main Authors: Töpfer-Petersen, E., Romero, A., Varela, P. F., Ekhlasi-Hundrieser, M., Dostàlovà, Z., Sanz, L., Calvete, J. J.
Format: Article
Language:English
Subjects:
Animals
Biological and medical sciences
capacitation
Carrier Proteins - physiology
Cell Adhesion Molecules - physiology
CUB domain
Fundamental and applied biological sciences. Psychology
gamete recognition
Glycoproteins - physiology
Humans
Male
Mammalian male genital system
Morphology. Physiology
Seminal Plasma Proteins
Seminal Vesicle Secretory Proteins
Spermadhesin
spermatozoa
Spermatozoa - metabolism
Spermatozoa - physiology
Vertebrates: reproduction
zona pellucida
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Summary:Summary Spermadhesins are a novel family of secretory proteins expressed in the male genital tract of pig, horse and bull. They are major products of the seminal plasma and have been found to be peripherally associated to the sperm surface. The structure and function of spermadhesins have been thoroughly investigated in the pig, which exhibits the greatest diversity of members: AWN, AQN‐1, AQN‐2, PSP‐I and PSP‐II and its glycosylated isoforms. They are multifunctional proteins showing a range of ligand‐binding abilities, e.g. carbohydrates, sulfated glycosamino‐glycans, phospholipids and protease inhibitors, suggesting that they may be involved in different steps of fertilization. Isolated porcine spermadhesins bind the zona pellucida glycoproteins in a cation‐dependent manner with a Kd in a low micromolar range, and AWN, AQN‐1 and AQN‐3 display similar binding affinity for glyoproteins containing Galβ(1–3)‐GalNAc and Galβ(1–4)‐GlcNAc sequences in O‐linked and N‐linked oligosaccharides, respectively. During sperm passage through the epididymis AQN‐3 and AWN have been shown to bind tightly to the sperm surface by interaction with the phospholipids of the membrane bilayer. At ejaculation the spermadhesins form a protective coat around the sensitive acrosomal region of the sperm head, thus possibly preventing premature acrosome reaction. During in vitro capacitation most of these aggregated sperm adhesins are lost, with the exception of phospholipid‐bound spermadhesins. AWN and AQN‐3 may now serve as a primary receptor for the oocyte zona pellucida, thus contributing to initial binding and recognition between sperm and egg. The amino acid sequence of spermadhesins does not show any discernible similarity with known carbohydrate recognition domains (CRD). However, they belong to the superfamily of proteins with a CUB domain with a predicted all‐β structure. The crystal structure of the heterodimeric complex of the spermadhesins PSP‐I/PSP‐II has been solved, showing that the overall structure of both spermadhesins consists of a β‐sandwich with five (parallell and antiparallel) β‐strands. It is the first three‐dimensional structure of a zona pellucida‐binding protein and reveals the architecture of the CUB domain. The spermadhesins represent a novel class of lectins that may be involved in sequential steps of fertilization, at least in the pig.
ISSN:0303-4569
1439-0272
DOI:10.1111/j.1439-0272.1998.tb01163.x