ARABINOGALACTAN-PROTEINS FROM NICOTIANA-ALATA AND PYRUS-COMMUNIS CONTAIN GLYCOSYLPHOSPHATIDYLINOSITOL MEMBRANE ANCHORS

Arabinogalactan-proteins (AGPs) are a class of proteoglycans found in cell secretions and plasma membranes of plants, Attention is currently focused on their structure and their potential role in growth and dev elopment. We present evidence that two members of a major class of AGP s, the classical AGPs, AGPNa1 from styles of Nicotiana alata and AGPPc 1 from cell suspension cultures of Pyrus communis, undergo C-terminal processing involving glycosylphosphatidylinositol membrane anchors. Th e evidence is that (i) the transmembrane helix at the C terminus predi cted from the cDNA encoding these proteins is not present-the C-termin al amino acid is Asn(87) and Ser(97) for AGPNa1 and AGPPc1, respective ly; (ii) both AGP protein backbones are substituted with ethanolamine at the C-terminal amino acid; and (iii) inositol, glucosamine, and man nose are present in the native AGPs. An examination of the deduced ami no acid sequences of other classical AGP protein backbones shows that glycosylphosphatidylinositol-anchors may be a common feature of this c lass of AGPs.