Synthetic genes for the elucidation of glycosylation codes for arabinogalactan-proteins and other hydroxyproline-rich glycoproteins

Abstract

Hydroxyproline-rich glycoproteins (HRGPs) are ubiquitous architectural components of the growing plant cell wall, accounting for as much as 10-20% of the dry weight. HRGPs are implicated in all aspects of plant growth and development, including responses to stress. The HRGP superfamily contains three major groups which represent a continuum of peptide periodicity and hydroxyproline-O-glycosylation. These groups range from the highly periodic and lightly arabinosylated repetitive proline-rich proteins (PRPs), through the cross-linked extensins which are periodic and highly arabinosylated, to the arabinogalactan-proteins (AGPs) which are the most highly glycosylated and least periodic. The repetitive units are small, often only four- to six-residue-glycosylated modules viewed hypothetically as functional motifs, or glycomodules. The Hyp contiguity hypothesis predicts that Hyp arabinosylation increases with Hyp contiguity and that clustered noncontiguous Hyp residues are sites of arabinogalactan polysaccharide addition in the AGPs and gums. Recent results involving glycosylation site mapping of endogenous HRGPs and HRGP design using synthetic genes have corroborated the hypothesis. The uses of synthetic genes in HRGP glycosylation site mapping and structural/functional analysis are also discussed.

Arabinogalactan-proteins: structure, expression and function

“…In other words, for AGPs, isolated Hyp residues appearing in the core protein are predicted to be the points of attachment of polysaccharide chains, whereas clusters of Hyp residues are predicted to be the potential sites of attachment for oligoarabinoside chains approximately four to six residues in length. Such predictions need to be tested further, but in the limited number of cases tested thus far for various plant HRGPs, the predictions are well supported [32]. Some AGPs may also contain N-linked glycans as evidenced by the ability of peptide: N-glycosidase F to cleave TTS and NaPRP4 (i. e. GaRSGP) glycoproteins as well by direct sequencing of the N-linked chain of GaRSGP [26,27,A.…”

Arabinogalactan Proteins in Arabidopsis thaliana Pollen Development

“…The mature protein core is rich in Pro/Hyp, Ala, Ser and Thr, which compose specific repetitive sequence modules. The pattern of these modules presumably constitutes the code that accounts for the characteristic glycan chains present in AGPs (Kieliszewski & Shpak, 2001;Schultz et al, 2004;Showalter et al, 2010). The repetitive amino acid modules (such as AP, TP, SP, or combinations of these) are typically scattered throughout the sequence of the mature protein.…”

“…This classification is mainly based on the sugar content and glycosylation patterns (Kieliszewski & Shpak, 2001;Shpak et al, 1999) of the molecules, the AGPs being the most heavily glycosylated of all.…”

Aggregate structure of hydroxyproline-rich glycoprotein (HRGP) and HRGP assisted dispersion of carbon nanotubes

“…Hydroxyproline-rich glycoproteins (HRGPs) comprise a superfamily of extra-cellular structural proteins expressed in plant cell walls and extracellular matrix during normal development and in response to stress [1,2]. HRGPs are extended macromolecules consisting of small repetitive peptide and glycopeptide motifs.…”