Arabinogalactan-proteins: structure, expression and function

Abstract

Abstract. Arabinogalactan-proteins (AGPs) are a family of extensively glycosylated hydroxyproline-rich glycoproteins that are thought to have important roles in various aspects of plant growth and development. After a brief introduction to AGPs highlighting the problems associated with defining and classifying this diverse family of glycoproteins, AGP structure is described in terms of the protein component (including data from molecular cloning), carbohydrate component, processing of AGPs (including recent data on glycosylphosphatidylinositol membrane anchors) and overall molecular shape. Next, the expression of AGPs is examined at several different levels, from the whole plant to the cellular levels, using a variety of experimental techniques and tools. Finally, AGP function is considered. Although the existing functional evidence is not incontrovertible, it does clearly droxyproline poor, lightly glycosylated and largely unreactive with Yariv reagent. It is worth remembering that it is human nature to group and classify things to facilitate their comprehension and discourse, whereas Mother Nature simply constructs biological entities, including AGPs, using material at hand with blatant, pedagogical disregard. Structure Protein moietyKnowledge of the protein moieties of AGPs has mostly come from purifying AGPs, deglycosylating them and analyzing their respective core proteins by amino acid analysis and, to a more limited extent, by sequence analysis ( fig. 2) [3 -10]. More recently, molecular cloning of several confirmed and putative AGP core proteins has CMLS, Cell. Mol. Life Sci. 58 (2001) 1399 -1417 1420-682X/01/101399-19 $ 1.50 + 0.20/0 © Birkhäuser Verlag, Basel, 2001 CMLS Cellular and Molecular Life Sciences point to roles for AGPs in vegetative, reproductive, and cellular growth and development as well as programmed cell death and social control. In addition and most likely inextricably linked to their functions, AGPs are presumably involved in molecular interactions and cellular signaling at the cell surface. Some likely scenarios are discussed in this context. AGPs also have functions of real or potential commercial value, most notably as emulsifiers in the food industry and as potential immunological regulators for human health. Several important questions remain to be answered with respect to AGPs. Clearly, elucidating the unequivocal functions of particular AGPs and relating these functions to their respective structures and modes of action remain as major challenges in the years ahead.

Mucilage chemical profile and antioxidant properties of giant swamp taro tubers

“…According to Kishk and Al-Sayed (2007), glycoproteins contained in mucilages are equally increasingly being sought after for their emulsifying role in certain food processes. The report of their role as potential immunological regulators (Showalter 2001) as well as antioxidants (Fan et al 2007) in human health has further heightened the research interest on the different sources and characteristics of mucilage. This is achieved in some cases by activating the complement system and in other cases by enhancing the cytotoxic activity of natural killer cells, and this has been associated with their content in Arabinogalactan-proteins (AGP).…”

Characterization of an Exo-β-1,3-D-galactanase fromStreptomyces avermitilisNBRC14893 Acting on Arabinogalactan-Proteins

“…They are found in the extracellular matrix associated with the plasma membrane and cell wall of higher plants. 1,2) AGPs are implicated in several aspects of cell wall biology including the signalling of cell context and cell expansion, yet remain elusive in terms of their mechanistic involvement in cell processes. 1,2) They comprize a large gene family in Arabidopsis thaliana, with almost 50 members.…”

“…1,2) AGPs are implicated in several aspects of cell wall biology including the signalling of cell context and cell expansion, yet remain elusive in terms of their mechanistic involvement in cell processes. 1,2) They comprize a large gene family in Arabidopsis thaliana, with almost 50 members. 1,2) Structural and immunochemical analyses reveal considerable heterogeneity to the arabinogalactan component, which can account for over 90% of AGP mass.…”

“…1,2) They comprize a large gene family in Arabidopsis thaliana, with almost 50 members. 1,2) Structural and immunochemical analyses reveal considerable heterogeneity to the arabinogalactan component, which can account for over 90% of AGP mass. 1,2) The carbohydrate moieties of AGPs have a common structure consisting of -1,3-galactosyl backbones (sugars in the present study are D series unless otherwise designated) possessing mono or oligo -1,6-galactosyl and/or arabinosyl side chains.…”

“…1,2) Structural and immunochemical analyses reveal considerable heterogeneity to the arabinogalactan component, which can account for over 90% of AGP mass. 1,2) The carbohydrate moieties of AGPs have a common structure consisting of -1,3-galactosyl backbones (sugars in the present study are D series unless otherwise designated) possessing mono or oligo -1,6-galactosyl and/or arabinosyl side chains. L-Arabinose and lesser amounts of other auxiliary sugars, such as glucuronic acid, L-rhamnose, and L-fucose, are attached to the side chains, usually at non-reducing termini.…”