The occurrence of novel 9-O-sulfated N-glycolylneuraminic acid-capped alpha2-->5-Oglycolyl-linked oligo/polyNeu5Gc chains in sea urchin egg cell surface glycoprotein. Identification of a new chain termination signal for polysialyltransferase.
We report the isolation and structural characterization of an oligo/polysialic acid-containing glycopeptide fraction (designated ESP-Sia) prepared from the egg cell surface complex of the sea urchin, Hemicentrotus pulcherrimus, by exhaustive pronase treatment. The carbohydrate chains isolated from ESP-Sia were shown to consist of O-linked oligo/polysialic acid-containing glycan units and N-linked carbohydrate chains. The present studies have revealed that the O-linked oligo/polysialic acid-containing glycan chains derived from the ESP-Sia were similar to those present in egg jelly coat polysialylated glycoprotein in being composed of tandem repeats of N-glycolylneuraminic acid (Neu5Gc) glycosidically linked in a novel fashion through the glycolyl group, (-->5-OglycolylNeu5Gcalpha2-->)n. However, they differ from the egg jelly coat in two key respects. First, the average degree of polymerization of the oligo/polysialic acid chains of ESP-Sia is only 3; a value far lower than that found in the jelly coat glycoprotein (average degree of polymerization was about 20). Second, ESP-Sia is uniquely characterized by the presence of 9-O-sulfated N-glycolylneuraminic acid (Neu5Gc9HSO3) residues at the nonreducing termini of the (-->5-OglycolylNeu5Gcalpha 2-->)n chains. The terminal sialyl residues in the Neu5Gc9HSO3 alpha2-->(-->5-OglycolylNeu5Gcalpha2-->)n chains were totally resistant to exosialidases. The discovery of Neu5Gc9HSO3 as the nonreducing terminal residue of oligo/poly(-->5-OglycolylNeu5Gcalpha 2-->) group is especially noteworthy in that Neu5Gc9HSO3 appears to be of limited distribution among glycoconjugates. Following the earlier discovery of oligo/polysialic acid chains capped with KDN, i.e. KDN alpha2-->(-->8Neu5Gcalpha2-->)n, found in rainbow trout egg polysialoglycoproteins, it now appears that the sulfated Neu5Gc can serve a similar capping function.
Kitazume
S
S
Department of Biophysics and Biochemistry, Graduate School of Science, University of Tokyo, Hongo-7 Tokyo 113, Japan.
Kitajima
K
K
Inoue
S
S
Haslam
S M
SM
Morris
H R
HR
Dell
A
A
Lennarz
W J
WJ
Inoue
Y
Y
D000107:Acetylation; D000818:Animals; D002240:Carbohydrate Sequence; D002851:Chromatography, High Pressure Liquid; D002852:Chromatography, Ion Exchange; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy; D008562:Membrane Glycoproteins / Q000737:chemistry*; D008969:Molecular Sequence Data; D009438:Neuraminic Acids / Q000737:chemistry*; D010063:Ovum / Q000737:chemistry*; D010443:Peptide Chain Termination, Translational; D012617:Sea Urchins; D013464:Sulfuric Acids / Q000737:chemistry
D008562:Membrane Glycoproteins; D009438:Neuraminic Acids; D013464:Sulfuric Acids; C032592:N-glycolylneuraminic acid