Table 1.
Classical AGPs: molecular properties
| Distribution: | ∼80 % periplasmic, ∼20 % cell wall; T = M + S + W |
| T = total AGPs; M = membrane-bound; S = soluble after cell breakage; M + S = periplasmic W = wall-bound. | |
| Quantification: e.g. BY-2 cells T = 600 μg AGPs g f. wt (Lamport et al., 2006) | |
| Molecular Size: | ∼120 kDa = ∼3 × 60 nm (Zhao et al., 2002) |
| Genes: | ∼19 in Arabidopsis (Schultz et al., 2000) |
| 13 in rice (Yang et al., 2007; Ma and Zhao, 2010; Showalter et al., 2010) | |
| At 17,18 & 19 (null; Coimbra et al., 2009) have a Lys-rich subdomain (Yang et al., 2007) | |
| eb1 is deficient in Gal synthesis (UDPGlc epimerase; Seifert et al., 2002) | |
| AtAGP17 (rat1) decreases Agrobacterium transformation (Gaspar et al., 2004) | |
| Polypeptide: | 87–739 aa residues in extended conformation (Showalter et al., 2010) |
| Hyp, Ala, Ser, dominate | |
| Lack Tyr, Phe, Trp and Cys | |
| Subdomain often a 12-r Lys-rich (Gao et al., 1999; Zhao et al., 2002; Yang et al., 2005, 2007) | |
| Glycosylation motifs: SP AP TP VP (Tan et al., 2003) | |
| Polysaccharide: | Arabinogalactan ‘beads’ or Hyp–AG glycomodules |
| Size: 15–150 sugar residues | |
| Backbone: β-1,3-linked galactose trisaccharides β-1,6-linked (Tan et al., 2004, 2010) | |
| Sidechains: bifurcated (Ara)3-Gal-(Rha-GlcU; Tan et al., 2010) | |
| Yariv reactivity: contentious; see text | |
| Post-translational modifications: | N-terminal signal peptide (Schultz et al., 2000) |
| C-terminal GPI lipid anchor (Oxley and Bacic, 1999; Svetek et al., 1999; Borner et al., 2003) | |
| Hydroxylation of peptidyl Pro via direct O2 fixation (Lamport, 1963a) | |
| O-Hyp glycosylation rules (no N-glycosylation) | |
| Non-contiguous Hyp–AG polysaccharides (Zhao et al., 2002) | |
| Contiguous Hyp short arabino-oligosaccharides | |
| 12 to 24 acidic Hyp–AGs (15–150 residues; Zhao et al., 2002) | |
| An Hyp–AG has 1 to 15 AG subunits | |
| AG subunit is a repetitive glycomotif of ∼15 sugar residues | |
| Glycomotif consensus: Ara6 Gal5 GlcA2 Rha2 | |
| AG bifurcated sidechain: Rha, GlcA, Ara3, Gal | |
| Lack fucose with exceptions (Wu et al., 2008, 2010) | |
| Glycomotif linkage analysis (mol %): | |
| Main chain: 3,6-Gal ×2 (13·3 %) 6-Gal ×1 (6·7 %)* | |
| Sidechain: 3,6-Gal ×2 4-GlcA ×2 | |
| 3,5-Ara ×2 t- Rha ×2 | |
| 3-Ara ×2 t- Ara ×2 | |
| Calcium binding: | GlcU/Ca2+ molar ratio 2:1 |
| ∼30 Ca2+-binding subunits/120 kDa AGP† |
* 6-linked Gal connects repetitive subunits (glycomotifs).
† AGPs approx. 120 kDa bind approx. 1 % Ca2+ w/w = 1·2 kDa Ca2+. Thus, moles bound Ca2+ = 1·2 kDa/40 Da.