Structural analysis of linear hydroxyproline-bound O-glycans of Chlamydomonas reinhardtii—conservation of the inner core in Chlamydomonas and land plants

Linear hydroxyproline-bound O-glycans of the unicellular green alga Chlamydomonas reinhardtii were isolated from outer cell wall glycoproteins and their structure elucidated by chemical and spectroscopic methods. They consist exclusively of arabinose and galactose, the latter in the furanose form, unusual for plants. The first two arabinoses linked to hydroxyproline have the same anomeric configuration and linkage to each other as do the arabinosides isolated from land plants, suggesting that these two steps of hydroxyproline-O-glycosylation have been conserved during evolution. In a concomitant analysis of Hyp-bound O-tri- and tetraarabinans isolated from Arabidopsis thaliana, we were able to unambiguously identify the natural trans-4-l-Hyp-bound O-glycans and the artificially produced d-allo forms and to identify diagnostic signals in NMR spectra of these compounds for the first time.

The structure of the most abundant linear hydroxyproline-bound O-glycans found in cell wall glycoproteins of Chlamydomonas reinhardtii were elucidated by ESI-MS, GC–MS and NMR. While the inner core consisting of two β-1→2-linked arabinoses is found in land plants as well, galactofuranoses are novel constituents and Chlamydomonas-specific.Figure optionsDownload as PowerPoint slide