Presence of a Glycosylphosphatidylinositol Lipid Anchor on Rose Arabinogalactan Proteins

Abstract

Arabinogalactan proteins constitute a class of plant cell surface proteoglycans with widespread occurrence and suggested functions in various aspects of plant growth and development, including cell proliferation, expansion, marking, and death. Previous investigations of subcellular fractions from suspension-cultured cells of "Paul's Scarlet" rose (Rosa sp.) have revealed extensive structural similarity between some soluble arabinogalactan proteins from the cell wall space and some plasma membrane-associated arabinogalactan proteins, thus inspiring the present investigation of the mechanism through which these inherently water-soluble molecules are held on the plasma membrane. Several lines of evidence gained through a combination of methods including reversed-phase chromatography, treatment with phosphatidylinositol-specific phospholipase C, and chemical structural analysis now show that some rose arabinogalactan proteins carry a ceramide class glycosylphosphatidylinositol lipid anchor. The predominant form of the ceramide is composed of tetracosanoic acid and 4-hydroxysphinganine. Plasma membrane vesicles readily shed arabinogalactan proteins by an inherent mechanism that appears to involve a phospholipase. This finding has significance toward understanding the biosynthesis, localization, and function of arabinogalactan proteins and toward stimulating other studies that may expand the currently very short list of higher plant proteins found to carry such membrane lipid anchors.

Arabinogalactan-proteins: structure, expression and function

“…Vol. 58,2001 Multi-author Review Article cleaved in vitro and in vivo to release proteins, including AGPs, from the plasma membrane [33,34]. Thus, the model that emerges is that AGPs containing a GPI anchor are associated with the plasma membrane and are cleaved so as to release the AGP to and beyond the cell wall.…”

Role of the Extensin Superfamily in Primary Cell Wall Architecture

“…Hydrophilic AGPs may also behave as self-assembling amphiphiles that are inserted into the membrane in an orderly fashion (Gens et al, 2000), where they are initially bound by their C-terminal hydrophobic glycosylphosphatidylinositol-lipid anchor (Oxley and Bacic, 1999;Svetek et al, 1999;Borner et al, 2002). However, Hyp-arabinogalactans of AGPs likely play a role that differs from neutral Hyp-arabinosides of extensin.…”

Arabinogalactan Proteins in Arabidopsis thaliana Pollen Development

“…As opposed to the majority of known GPI anchors, whose lipid part is diacylglycerol-based, the inositolphospholipid part of the only two plant GPI anchors characterized to date is an inositolphosphoceramide (Oxley & Bacic, 1999;Svetek et al, 1999).…”