title: Carbohydrate binding properties and carbohydrate induced conformational switch in sheep secretory glycoprotein (SPS-40): crystal structures of four complexes of SPS-40 with chitin-like oligosaccharides.
abstract: Crystal structures of four complexes of sheep secretory glycoprotein (SPS-40) with N-acetylglucosamine oligosaccharides (GlcNAc(n), (n=3-6)) have been determined at moderate resolutions. The binding studies of SPS-40 have been carried out using fluorescence spectroscopy and Surface Plasmon Resonance (SPR). Structure determinations of four complexes have shown a novel binding pattern of GlcNAc(n) molecules to SPS-40. The results indicate that the most preferred recognition region in the carbohydrate binding groove in SPS-40 is at subsites -4 to -2 among which subsite -2 provides the maximum interactions with carbohydrate residues. These structures have also shown that the interactions of GlcNAc3 and GlcNAc4 do not perturb the protein structure and those of GlcNAc5 induce partial conformational changes while in the case of GlcNAc6 the partially closed binding groove opened up completely. As in other SPX-40 structures, SPS-40 structure contains three overlapping flexible surface segments, His188-His197, Phe202-Arg212 and Phe244-Pro260 with several charged residues protruding outwardly. It creates a cluster of positive charges with a flexible base thus indicating a good scope of promoting the intermolecular interactions. This protein is glycosylated at Asn39 and may recognize other receptors having sugar binding sites. It appears that SPS-40 may involve both carbohydrate and protein bindings. The systematic carbohydrate-binding studies and the detailed structural results of four protein-carbohydrate complexes provide an excellent insight into the mechanism of carbohydrate binding. These are the first studies of this kind on secretory glycoproteins and their interactions with carbohydrates.
authors.affiliation: Department of Biophysics, All India Institute of Medical Sciences, New Delhi 110029, India.
authors.forename: Devendra B
authors.initials: DB
authors.lastname: Srivastava
authors.forename: Abdul S
authors.initials: AS
authors.lastname: Ethayathulla
authors.forename: Janesh
authors.initials: J
authors.lastname: Kumar
authors.forename: Rishi K
authors.initials: RK
authors.lastname: Somvanshi
authors.forename: Sujata
authors.initials: S
authors.lastname: Sharma
authors.forename: Sharmistha
authors.initials: S
authors.lastname: Dey
authors.forename: Tej P
authors.initials: TP
authors.lastname: Singh
mesh_terms: D000116:Acetylgalactosamine / Q000737:chemistry; D000595:Amino Acid Sequence; D000818:Animals; D002241:Carbohydrates / Q000737:chemistry; D002686:Chitin / Q000737:chemistry*; D018360:Crystallography, X-Ray; D006023:Glycoproteins / Q000737:chemistry*; D008969:Molecular Sequence Data; D009844:Oligosaccharides / Q000737:chemistry*; D011487:Protein Conformation; D012756:Sheep / Q000378:metabolism*; D013050:Spectrometry, Fluorescence; D020349:Surface Plasmon Resonance
chemical_list: D002241:Carbohydrates; D006023:Glycoproteins; D009844:Oligosaccharides; D002686:Chitin; D000116:Acetylgalactosamine