title: (Quasi-)racemic X-ray structures of glycosylated and non-glycosylated forms of the chemokine Ser-CCL1 prepared by total chemical synthesis.
abstract: Our goal was to obtain the X-ray crystal structure of the glycosylated chemokine Ser-CCL1. Glycoproteins can be hard to crystallize because of the heterogeneity of the oligosaccharide (glycan) moiety. We used glycosylated Ser-CCL1 that had been prepared by total chemical synthesis as a homogeneous compound containing an N-linked asialo biantennary nonasaccharide glycan moiety of defined covalent structure. Facile crystal formation occurred from a quasi-racemic mixture consisting of glycosylated L-protein and non-glycosylated-D-protein, while no crystals were obtained from the glycosylated L-protein alone. The structure was solved at a resolution of 2.6-2.1 Å. However, the glycan moiety was disordered: only the N-linked GlcNAc sugar was well-defined in the electron density map. A racemic mixture of the protein enantiomers L-Ser-CCL1 and D-Ser-CCL1 was also crystallized, and the structure of the true racemate was solved at a resolution of 2.7-2.15 Å. Superimposition of the structures of the protein moieties of L-Ser-CCL1 and glycosylated-L-Ser-CCL1 revealed there was no significant alteration of the protein structure by N-glycosylation.
authors.affiliation: Departments of Chemistry: Biochemistry & Molecular Biology, Institute for Biophysical Dynamics, University of Chicago, Chicago, IL 60637 (USA); Current address: Department of Chemistry, Graduate School of Science, Osaka University, Toyonaka, Osaka, 560-0043, JAPAN.. skent@uchicago.edu, rokamoto@chem.sci.osaka-u.ac.jp, rokamoto@chem.sci.osaka-u.ac.jp.
authors.forename: Ryo
authors.initials: R
authors.lastname: Okamoto
authors.forename: Kalyaneswar
authors.initials: K
authors.lastname: Mandal
authors.forename: Michael R
authors.initials: MR
authors.lastname: Sawaya
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Kajihara
authors.forename: Todd O
authors.initials: TO
authors.lastname: Yeates
authors.forename: Stephen B H
authors.initials: SB
authors.lastname: Kent
mesh_terms: D054402:Chemokine CCL1 / Q000737:chemistry*; D006031:Glycosylation; D012694:Serine / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D054402:Chemokine CCL1; D012694:Serine
keywords: X-ray structure; chemical protein synthesis; glycoprotein; mirror image proteins; quasi-racemic crystals