Glycosides of hydroxyproline: Some recent, unusual discoveries

Abstract

Glycosides of hydroxyproline (Hyp) in the plant cell wall matrix were discovered by Lamport and co-workers in the 1960s. Since then, much has been learned about these Hyp-rich glycoproteins. The intent of this review was to compare and contrast some less common structural motifs, in nontraditional roles, to uncover themes. Arabinosylation of short-peptide plant hormones is essential for growth, cell differentiation and defense. In a very recent development, prolyl hydroxylase and arabinosyltransferase activity has been shown to have a direct impact on the growth of root hairs in Arabidopsis thaliana. Pollen allergens of mugwort and ragweed contain proline-rich domains that are hydroxylated and glycosylated and play a structural role. In the case of mugwort, this domain also presents a significant immunogenic epitope. Major crops, including tobacco and maize, have been used to express and produce recombinant proteins of mammalian origin. The risks of plant-imposed glycosylation are discussed. In unicellular eukaryotes, Skp1 (a subunit of the E3(SCF) ubiquitin ligase complex) harbors a key Hyp residue that is modified by a linear pentasaccharide. These modifications may be involved in sensing oxygen levels. A few studies have probed the impact of glycosylation on the structure of Hyp-containing peptides. These have necessarily looked at small, synthetic molecules, since natural peptides and proteins are often isolable in only minuscule amounts and/or are heterogeneous in nature. The characterization of native structural motifs, together with the determination of glycopeptide conformation and properties, holds the key to rationalizing nature's architectural design.

Pea Border Cell Maturation and Release Involve Complex Cell Wall Structural Dynamics

“…Extensins also have been implicated in cell elongation (Velasquez et al, 2011;Taylor et al, 2012;Nguema-Ona et al, 2014). Although less pronounced than for XyG, we also observed a polarized distribution of extensin epitopes recognized by the mAbs LM1, LM3, and JIM20 (Fig.…”

Proline Editing: A General and Practical Approach to the Synthesis of Functionally and Structurally Diverse Peptides. Analysis of Steric versus Stereoelectronic Effects of 4-Substituted Prolines on Conformation within Peptides

“…In addition, recent work has found that proteins may be phosphorylated and glycosylated on hydroxyproline residues, suggesting a richer range of post-translational modifications accessible in this residue. 22 In order to address these questions, both 4 R and 4 S diastereomers of hydroxyproline were modified to the phosphorylated and to the diethylphosphate triester forms (Scheme 14, 97 - 100 ). Notably, phosphorylation ionization state changes as a function of pH, and therefore the structure of peptides with phosphorylated hydroxyproline could change as a function of pH.…”

Transient Glyco-Engineering to Produce Recombinant IgA1 with Defined N- and O-Glycans in Plants

“…Plant O -glycosylation differs significantly from mammals as plants do not have a functional mucin-type O -glycosylation pathway ( Castilho et al, 2012 ; Yang et al, 2012 ). Plants, on the other hand, can convert proline residues adjacent to O -glycosylation sites into hydroxyproline (Hyp; Taylor et al, 2012 ). Serine residues next to specific Hyp-sequence motifs may be modified with single galactose and Hyp residues and can be extensively modified with arabinose chains or arabinogalactans ( Seifert and Roberts, 2007 ; Basu et al, 2013 ; Saito et al, 2014 ).…”