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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.
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.
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.
Procollagen-proline dioxygenase catalyzes the following reaction: L-proline + alpha-ketoglutaric acid + O 2 → (2S, 4R)-4-hydroxyproline + succinate + CO 2. The mechanism for the reaction is similar to that of other dioxygenases, and occurs in two distinct stages: [3] In the first, a highly reactive Fe(IV)=O species is produced.
Structurally, the lamp proteins consist of two internally homologous lysosome-luminal domains separated by a proline-rich hinge region; at the C-terminal extremity there is a transmembrane region (TM) followed by a very short cytoplasmic tail (C). In each of the duplicated domains, there are two conserved disulfide bonds. This structure is ...
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 ...
The two most common linkages in glycoproteins are N-linked and O-linked glycoproteins. [3] An N-linked glycoprotein has glycan bonds to the nitrogen containing an asparagine amino acid within the protein sequence. [4] An O-linked glycoprotein has the sugar is bonded to an oxygen atom of a serine or threonine amino acid in the protein. [4]