title: Crystal structure of a secretory signalling glycoprotein from sheep at 2.0A resolution.
abstract: A 40kDa glycoprotein from dry secretion of sheep is implicated as a signaling factor and is named as SPS-40. This protein is secreted only during the early phase of involution when the drastic tissue remodeling occurs in the mammary gland. SPS-40 was purified from sheep dry secretions and crystallized using hanging drop vapour diffusion method. The crystals belong to orthorhombic space group P2(1)2(1)2(1) with cell dimensions, a=62.7A, b=66.4A, c=107.5A. The protein was also cloned for the determination of its complete amino acid sequence. The three-dimensional structure of SPS-40 was determined by X-ray crystallographic method at 2.0A resolution. The structure revealed the presence of an N-linked glycan chain at Asn39. The protein adopts a conformation with a classical (beta/alpha)(8)-barrel fold of triosephosphate isomerase (TIM) (residues 1-237 and 310-360) with an insertion of a small (alpha+beta) domain (residues 240-307) similar to that observed in chitinases. However, the Leu substitution for Glu in the consensus catalytic sequence in SPS-40 causes a loss of chitinase activity. Furthermore, the sugar-binding groove in SPS-40 is distorted considerably from the standard chitin-binding site in chitinase enzymes and hence the binding of chitin-like oligosaccharides is considerably hampered. Three surface loops, His188-His197, Phe202-Arg212 and Phe244-Pro260 have exceptionally high values of B-factors (average=70.5A(2)), indicating the presence of a less defined region.
authors.affiliation: Department of Biophysics, All India Institute of Medical Sciences, Ansari Nagar, New Delhi 110029, India.
authors.forename: Devendra B
authors.initials: DB
authors.lastname: Srivastava
authors.forename: A S
authors.initials: AS
authors.lastname: Ethayathulla
authors.forename: Janesh
authors.initials: J
authors.lastname: Kumar
authors.forename: Nagendra
authors.initials: N
authors.lastname: Singh
authors.forename: Sujata
authors.initials: S
authors.lastname: Sharma
authors.forename: Utpal
authors.initials: U
authors.lastname: Das
authors.forename: A
authors.initials: A
authors.lastname: Srinivasan
authors.forename: Tej P
authors.initials: TP
authors.lastname: Singh
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites / Q000235:genetics; D018360:Crystallography, X-Ray / Q000379:methods*; D005260:Female; D006023:Glycoproteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D034561:Sheep, Domestic; D013329:Structure-Activity Relationship
chemical_list: D006023:Glycoproteins