Chemistry Reference
In-Depth Information
Table 24.2
Examples for proteins on sperm with binding properties to ZP glycans.
Localization
Name
Species
Carbohydrate ligand
Sperm head surface
Mouse
Man
α
- mannosidase
β
1,4GalT - I
a
Mouse
GlcNAc
Asialoglycoprotein receptor 2
Rat
Gal
Spermadhesins
Pig
Gal
1,4GlcNAc,
sulfated glycosaminoglycans
β
1,3GalNAc, Gal
β
Acrosome
Acrosin
b
Mouse
Sulfated glycans
Bindin
See urchin
350 - kDa glycoprotein with sulfated and
sialylated
O
- glycans, sulfated fucans
P - Selectin
Pig
Not yet characterized
c
Sp17
Mouse
Heparin
Sp38
Pig
Sulfated glycoproteins
Sp56
Mouse
O
- Linked oligosaccharides of ZP3
Zonadhesin
Pig
Sulfated glycans
a
1,4 - galactosyltransferase.
b
Protease with a lectin site (see Table 19.2 ) .
c
For information on P-selectin ligands in the immune system, please see Chapter 27 .
β
turned out to be a potent competitor of sperm binding to the ZP (for Lewis
carbohydrate structures, please see Table 7.4) [6]. Studies in cattle strongly suggest
that
-
D
-Man residues at the nonreducing ends of high-mannose-type
N
- glycans
play an essential role in ZP binding and fertilization [5]. In humans and rats sperm
penetration through the ZP was inhibited by pretreatment of the sperm with
D
-mannose. In guinea pigs, hamsters, rats and humans,
L
- Fuc and fucoidin, a
sulfated fucan from algae, also active to block selectin binding in infl ammation
(please see Chapter 27 for details), were shown to be potent inhibitors of sperm-
ZP interaction. The latter fi ndings intimate that sperm binding to the ZP engages
a ' selectin - like ' interaction [1] (for information on selectins, please see Chapters
16 , 19 , 23 and 27). From looking at carbohydrate ligands of the ZP we next turn
to the question of the corresponding carbohydrate receptors of sperm.
Table 24.2 presents a survey of prominent sperm head surface proteins and
acrosomal proteins with binding properties to glycans [7, 8]. The latter are only
released or exposed after induction of the acrosome reaction (see above). Appar-
ently, the heterogeneity, complexity and high coding capacity of mammalian ZP
glycans is paralleled by the evolution of multiple sperm receptors for the ZP (see
also Table 18.2 and Table 19.1 for the diversity of structural folds with lectin activ-
ity). In each species, sperm-ZP interaction appears to be based on the cooperation
of multiple ligand-receptor systems with inherent redundancy to compensate a
loss (a similar redundancy is also seen in bacterial adhesion, see Chapter 17). Due
to the high degree of evolutionary divergence the key ligands and receptors will
have to be identifi ed individually in each species of interest. In the following, we
move on from the ZP and its relevance for mammalian fertilization to early
embryo development.
α
