Glycobiology Advance Access originally published online on October 11, 2006
Glycobiology 2007 17(2):157-164; doi:10.1093/glycob/cwl058
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Occurrence of a nonsulfated chondroitin proteoglycan in the dried saliva of Collocalia swiftlets (edible bird's-nest)
3 Department of Biochemistry, Tulane University Health Sciences Center School of Medicine, New Orleans, LA 70112
4 Department of Applied Biological Sciences, Saga University, Saga 840-8502, Japan
5 Department of Biochemistry, Kobe Pharmaceutical University, Higashinada-ku, Kobe 658-8558, Japan
6 Laboratory of Proteoglycan Signaling and Therapeutics, Faculty of Advanced Life Science, Hokkaido University, Frontier Research Center for Post-Genomic Science and Technology, Kita 21-jo, Nishi 11-choume, Kita-ku, Sapporo 001-0021, Japan
1 To whom correspondence should be addressed; Tel.: (504)-988-2451; Fax: (504)-988-2739; e-mail: yli1{at}tulane.edu
Received on June 19, 2006; revised on September 27, 2006; accepted on September 29, 2006
Despite their wide occurrence, proteoglycans (PGs) have never been isolated from the saliva of higher animals. We found that the Collocalia glycoproteins isolated from edible birds'-nests (the dried forms of regurgitated saliva of male Collocalia swiftlets) were rich in a PG containing nonsulfated chondroitin glycosaminoglycans (GAGs). We have devised a method to isolate a PG from the water extract of the white nest built by Aerodramus fuciphagus (white nest swiftlets) with a yield of 2-mg PG per gram nest. This PG contained 83% of carbohydrates, of which 79% were GalNAc and GlcUA (D-glucuronic acid) in an equimolar ratio. By using chondroitin AC lyase, the structure of GAGs in this PG was established to be chondroitin ( 
4GlcUAß1 3GalNAcß1 )n chains. The average molecular mass of the chondroitin chain was estimated to be 49 kDa by gel filtration. We have isolated a linkage region hexasaccharide, 
HexUA
1 3GalNAcß1 4GlcUAß1 3Galß1 3Galß1 4Xyl, from this PG by chondroitinase ABC digestion to show that the GAGs in this PG are also linked to the core protein through the common tetrasaccharide linker, GlcUAß1 3Galß1 3Galß1 4Xyl, found in various PGs. As water was not effective in extracting uronic acid-containing glycoconjugates from the black nest built by black nest swiftlets (A. maximus), we used 4 M guanidium chloride and anion-exchange chromatography in the presence of urea to extract and isolate about 30 mg of a chondroitin PG preparation from 10 g of the desialylated black nest. As the biological significance of chondroitin is still not well understood, bird's nest should become a convenient source for preparing this unique GAG to study its biological functions.
Key words: chondroitin / proteoglycan / glycosaminoglycan / bird's nest / saliva
2 Present address: Department of Biochemistry, Faculty of Medicine, Chiang Mai University, Chiang Mai 50200, Thailand
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