Identification of sulfated oligosialic acid units in theO-linked glycan of the sea urchin egg receptor for sperm

Abstract

The Strongylocentrotus purpuratus sea urchin egg receptor for sperm is a cell surface glycoprotein with a molecular mass of 350 kDa. Recent studies indicate that the sulfated O-linked glycans isolated from the receptor bind to acrosome-reacted sperm. The purified receptor was analyzed with respect to amino acid and carbohydrate content and shown to be composed of 70% carbohydrate by weight. Compositional analysis indicated that both N-and O-linked oligosaccharide chains were present. After peptide:N-glycanase treatment of the receptor to remove most of the N-linked glycan chains, the majority of the sialic acid residues remained associated with the receptor and were shown by several types of experiments to be composed of sulfated oligosialic acid units attached to the O-linked glycan chains of the receptor. Chemical and physical studies on oligosialic chains discovered earlier in the Pronase-generated glycopeptide fraction isolated from the egg cell surface complex of another species of sea urchin, Hemicentrotus pulcherrimus, established that these molecules had the structure: (SO 4 ؊ )-9Neu5Gc␣2(35-O glycolyl Neu5Gc␣23) n . Based on comparative and analytical studies, it was concluded that this sulfated oligosaccharide is a component of a GalNAc-containing chain that is O-linked to the polypeptide chain of the sea urchin egg receptor for sperm. Using a competitive inhibition of fertilization bioassay it was shown that the sulfated oligosialic acid chains derived from the S. purpuratus egg cell surface complex inhibited fertilization; the nonsulfated form of this oligosialic chain had little inhibitory activity.In fertilization, cell surface molecules of the egg and sperm play a central role in the species-specific interactions that occur in many organisms (1, 2). In the case of the sea urchin, earlier studies showed that the sperm protein, bindin, which is a component of the acrosome granule, plays a key role in gamete recognition (3, 4). Following early work in which a high molecular weight glycoprotein on the egg cell surface was implicated as a receptor for sperm (5-7), it was shown that Pronase-generated glycopeptides prepared from this crude receptor preparation inhibited fertilization, but without species specificity (8, 9). Later, a cell surface glycoprotein with a molecular mass of 350 kDa was identified as the egg receptor in Strongylocentrotus purpuratus (10,11). This molecule, as well as a 70-kDa extracellular fragment generated by lysyl endoproteinase C digestion of intact eggs, were shown to contain sugars typical of both N-and O-linked oligosaccharides, as well as sulfate (10, 12). These oligosaccharide chains were fractionated, and the putative O-linked chains were shown to inhibit fertilization and bind without species specificity to acrosome-reacted, but not to unreacted sperm (13). In a subsequent study it was shown that attachment of these chains via a neoglycoprotein to beads mediated kinetically stable binding of sperm to such beads (14).In earlier studies, ␣235-O glycolyl -linked p...

Role of egg surface glycoconjugate in the fertilization of the rock shrimp Rhynchocinetes typus (Milne Edwards, 1837)

“…It is known that not all monosaccharides present in oocyte envelopes are directly involved with gamete interactions (Focarelli et al, 1988;Litscher & Honegger, 1991;Kitazume-Kawaguchi et al, 1997). The fucose, galactose and α-GalNAc detected in lowest concentration in oocyte envelopes of R. typus may be only a portion of structural oligosaccharide chains of glycoconjugates due to its low quantity in the envelope and absence of inhibition in the fertilization inhibition tests, and probably do not interact in the gamete recognition as suggested by Litscher & Honegger (1991) in oocytes of Phallusia mamillata and Ascidia malaca by O'Dell et al (1974).…”

Novel forms of protein glycosylation

“…The GIcNAc linked to the mannosc core structure was sulfated at position 6, in contrast to N-CA_M, which was substituted at position 3 [18]. Sulfated oligosialic acid units haxe been described in Olinked glycans of thc sea urchin egg reccptor for sperm [29]. Sulfatcd oligosaccharidc chains with thc novel structure (SO.~-9)NcuAcSGcc~2(-50~l,~,,blNeuSGcc~2-),~ were identified [291.…”

Review—Egg Cells on a Semiconductor: Potentials in Drug Screening and Clinical Diagnostics

“…In particular, molecular charges at the ovum surface of sea urchin might be significant for fertilization, because sulfated oligosialic acid units at the ovum surface of sea urchin functionate as receptor for sperm. 33 In this Real-time electrical detection of molecular charges at ovum membrane 10 section, we show the real-time electrical detection of intrinsic molecular charges of sialic acids and sulfated saccharides, which play an important role on fertilization, at the ovum surface of sea urchin by use of the FET devices.…”

“…Glycoproteins or glycolipids exist in the plasma membrane and have important roles in interactions of the cell with its surroundings. 32,33 Some of them have charges, exposing their sialic acid residues or sulfated saccharides at the cell surface. Information on molecular charges at the surface of cell membrane is therefore useful not only for understanding the cell functions but also for practical application.…”