Chaotrope-soluble cell wall glycoproteins of Volvox and some members of the Zygnematophyceae immunologically related to the ‘150 kDa’ cell wall glycoprotein of Chlamydomonas reinhardtii

Abstract

As previously described, the cell wall of Chlamydomonas reinhardtii contains several chaotrope-soluble glycoproteins with similar sugar compositions, but considerably different proportions of hydroxyproline. All these hydroxyproline-containing cell wall glycoproteins are recognized by a polyclonal antibody raised against the purified ‘150 kDa’ cell wall glycoprotein of Chlamydomonas reinhardtii. This antibody also cross-reacts with some polypeptides present in the LiCl-extracts from intact cells of Spirotaenia erythrocephala, Spirotaenia obscura, Volvox aureus, and Volvox globator as revealed by Western blot analyses. Therefore, an IgG fraction of this particular antibody coupled to CNBr-activated Sepharose was used to isolate the immunologically related polypeptides extracted by aqueous LiCl from intact cells or cell wall preparations of different green algae belonging to the Volvocales or to the Zygnematophyceae. Different and more or less complex polypeptide patterns were observed by comparative SDS-PAGE analyses of the polypeptide fractions isolated by immunoaffinity chromatography from extracts of Chlamydomonas reinhardtii, Volvox aureus, Micrasterias rotata, Gonatozygon brebissonii and Netrium digitus, respectively, whereas the corresponding fraction prepared from Spirotaenia erythrocephala contained a predominant ‘160 kDa’ component. Amino acid and sugar analyses revealed that all these polypeptide fractions contained hydroxyproline (1.0–4.5 mol%) and the same sugars as the Chlamydomonas cell wall glycoproteins. However, the relative amounts of these sugars (arabinose, galactose, glucose, mannose and xylose) were found to be rather different. The highest proportion of hydroxyproline (4.5 mol%) and the highest ratio of arabinose: galactose (4.75:1) were determined for the glycoprotein fraction isolated from Spirotaenia erythrocephala indicating that at least the predominant ‘160 kDa’ component is an intrinsic cell wall glycoprotein containing hydroxyproline and oligo-arabinosyl side chains. All the polypeptide fractions isolated from the other green algae obviously also contained chaotropesoluble cell wall glycoproteins as revealed by the presence of arabinose and hydroxyproline. These findings show that all the investigated green algae contain chaotrope-soluble cell wall glycoproteins immunologically related to the ‘150 kDa’ cell wall glycoprotein of Chlamydomonas reinhardtii.