Hydroxy-L-proline-rich glycoproteins

This evidence indicated the presence of two hydroxy-L-proline-rich glycoproteins in the primary cell-wall of suspension-cultured sycamore-cells one, a structural glycoprotein found only in the wall, and the second which, in culture, is present in the wall in only small proportions and is mainly found in the culture medium.57,234 These two glycoproteins appear to be unrelated structurally. 

The hydroxy-L-proline of the crude, mung-bean-wall preparation is not associated with the lectin259 this indicates a difference between the mung-bean-wall lectin and the lectin isolated from potato tubers. The latter is rich in hydroxy-L-proline, arabinose, and galactose260 in this respect, it shows features similar to those of the hydroxy-L-proline-rich glycoprotein ( extensin ) of the primary cell-wall, first reported by Lamport261 (see Section VII, 1). 

There is much evidence that the hydroxy-L-proline-rich glycoprotein is involved both in the mechanical properties of the wall and in rates of growth. Cleland514 516 showed that, in oat coleoptiles, removal of wall... 

Perhaps, therefore, the importance of wall-bound, hydroxy-L-proline-rich glycoprotein lies in a property other than the breaking of hydroxy-L-proline-arabinose cross-links between the glycoprotein and wall poly-... 

At this stage, the precise relationship between wall glycoprotein and cell extension remains a subject for speculation. Much more information is needed about the nature of the bonding, within the wall matrix, in which the hydroxy-L-proline-rich glycoprotein is involved, and about its... 

In Section III, it was mentioned that cell wall is a complex structure formed by different polysaccharides connected to glycoproteins. Hydroxy-L-proline-rich glycoproteins, such as extensin, have been found in almost all plants surveyed, and in some algae.203,281 A network of protein, pectic polymers, and xyloglucan, serving to cross-link the cellulose fibers of the cell wall, has been proposed.282,283 However, covalent links between the different components have not been demonstrated moreover, some of them can be extracted separately,284 and some associations may be artificial.285 Nevertheless, results are consistent with interactions through dipole-dipole (such as hydrogen bonds) or hydrophobic bonds. 

A fundamental role in cell extension has been proposed for hydroxy-L-proline-rich glycoproteins.286 Evidence for this involvement in cell extension... 

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