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Keywords:

  • Chemische Proteinsynthese;
  • Glykoproteine;
  • Quasiracemische Kristalle;
  • Röntgenkristallstrukturen;
  • Spiegelbildproteine

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.