title: NMR and molecular modeling studies on two glycopeptides from the carbohydrate-protein linkage region of connective tissue proteoglycans.
abstract: Complete 1H and 13C NMR assignments are reported for two glycopeptides representing the carbohydrate-protein linkage region of connective tissue proteoglycans. These glycopeptides are the octasaccharide hexapeptide, Ser(GlcpAbeta(1-->3) Galpbeta(1-->3)Galpbeta(1-->4)Xylpbeta)-Gly-Ser-Gly-Se r (GlcpAbeta(1-->3)Galpbeta(1-->3)Galpbeta(1-->4)Xylp beta)-Gly (1), and the tetrasaccharide dipeptide, Ser(GlcpAbeta(1-->3)Galpbeta(1-->3)Galpbeta(1-->4)X ylpbeta)-Gly (2). The vicinal coupling constant data show that the monosaccharide residues adopt4 C 1 chair conformations. Distance geometry/simulated annealing calculations using 2D NOESY derived distance constraints yielded a single family of structures for the tetrasaccharide moiety, with well defined interglycosidic linkage conformations. The straight phi torsion angles of the glycosidic C1'-O1 bonds showed a strict preference for the -sc range whereas the psi torsion angles (O1-Cn) exhibited dependence upon the interglycosidic linkage position (-ac for beta(1-->3) linkage, +ac for beta(1-->4) linkage). The predominant conformation about the glycopeptide bond is straight phi = -sc and psi = +ac. The presence of strong daN (i, i+1) NOE contacts, and the general absence of dNN (i, i+1) contacts (except for a weak Ser-5/Gly-6 dNN contact) and the dbN (i, i+1) contacts (except for Ser-1/Gly-2) in the ROESY spectrum, suggest that the backbone for 1 is predominantly in an extended conformation. A comparison of the ROESY data for 1 with those obtained from the unglycosylated hexapeptide (3) of the same sequence suggests that glycosylation has only a marginal influence on the backbone conformation of the hexapeptide.
authors.affiliation: Department of Biochemistry and Molecular Genetics, and Comprehensive Cancer Center, The University of Alabama at Birmingham, Birmingham, AL 35294-2041, USA.
authors.forename: P K
authors.initials: PK
authors.lastname: Agrawal
authors.forename: J C
authors.initials: JC
authors.lastname: Jacquinet
authors.forename: N R
authors.initials: NR
authors.lastname: Krishna
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D003238:Connective Tissue / Q000737:chemistry*; D006020:Glycopeptides / Q000737:chemistry*; D006031:Glycosylation; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D011509:Proteoglycans / Q000737:chemistry*
chemical_list: D006020:Glycopeptides; D011509:Proteoglycans