The glycocalyx of the sperm surface

The surface of mammalian spermatozoa is covered by a dense coating of carbohydrate-rich molecules forming a 20-60 nm thick glycocalyx. The majority of sugar residues are attached to proteins which are either integrated within the sperm membrane, or are more or less loosely associated with it. It is estimated that there may be several hundred different glycoproteins comprising the glycocalyx, some of which are synthesized within the testis. Others, however, are produced by the epithelia of the efferent ducts, epididymis and possibly other accessory glands, and become associated with the spermatozoa post-testicularly during transit through, and storage in, the male tract. The acquisition of the mature glycocalyx is associated with the attainment of full sperm fertilizing ability. Until its complete molecular structure is elucidated, the complex function of the glycocalyx remains obscure, though it may be related to membrane maturation and immunoprotection in the female tract, as well as to sperm-zona binding and fertilization.