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Other hydroxyprolines also exist in nature. The most notable ones are 2,3-cis-, 3,4-trans-, and 3,4-dihydroxyproline, which occurs in diatom cell walls [12] and are postulated to have a role in silica deposition. Hydroxyproline is also found in the walls of oomycetes, fungus-like protists related to diatoms.
Two tyrosines separated by a single amino acid, typically valine or another tyrosine, form a short intra-molecular diphenylether crosslink. [11] This can be crosslinked further by the enzyme extensin peroxidase [12] [13] [14] to form an inter-molecular bridge between extensin molecules and thus form networks and sheets.
They are members of the wider class of hydroxyproline (Hyp)-rich cell wall glycoproteins, a large and diverse group of glycosylated wall proteins. AGPs have been reported in a wide range of higher plants in seeds, roots, stems, leaves and inflorescences. AGPs account for only a small portion of the cell wall, usually no more than 1% of dry mass ...
Additionally, structural proteins (1-5%) are found in most plant cell walls; they are classified as hydroxyproline-rich glycoproteins (HRGP), arabinogalactan proteins (AGP), glycine-rich proteins (GRPs), and proline-rich proteins (PRPs). Each class of glycoprotein is defined by a characteristic, highly repetitive protein sequence.
In 1954, Ramachandran & Kartha (13, 14) advanced a structure for the collagen triple helix on the basis of fiber diffraction data. It consists of a triple helix made of the repetitious amino acid sequence glycine-X-Y, where X and Y are frequently proline or hydroxyproline. [2] [3] Collagen folded into a triple helix is known as tropocollagen.
Chlamydomonas reinhardtii is a single-cell green alga about 10 micrometres in diameter that swims with two flagella.It has a cell wall made of hydroxyproline-rich glycoproteins, a large cup-shaped chloroplast, a large pyrenoid, and an eyespot apparatus that senses light.
The systematic name of this enzyme class is UDP-N-acetyl-D-glucosamine:[Skp1-protein]-hydroxyproline N-acetyl-D-glucosaminyl-transferase. Other names in common use include Skp1-HyPro GlcNAc-transferase , UDP-N-acetylglucosamine (GlcNAc):hydroxyproline polypeptide , GlcNAc-transferase , UDP-GlcNAc:Skp1-hydroxyproline GlcNAc-transferase , and UDP ...
In 2001, biologically active hydroxyproline-rich glycopeptides were isolated from tobacco which activated the production of protease inhibitors in a similar way to systemin in tomatoes. [1] Although they are structurally unrelated to systemins, their similar function resulted in them being named hydroxyproline-rich systemins (HypSys).