Prolyl Hydroxylase Paralogs in Show High Similarity With Regard to Substrate Specificity.

Plant glycoproteins display a characteristic type of -glycosylation where short arabinans or larger arabinogalactans are linked to hydroxyproline. The conversion of proline to 4-hydroxyproline is accomplished by prolyl-hydroxylases (P4Hs). Eleven putative P4Hs, which fall in four homology groups, have been identified by homology searches using known P4H sequences. One member of each of these groups has been expressed in insect cells using the baculovirus expression system and applied to synthetic peptides representing the -glycosylated region of erythropoietin (EPO), IgA1, Art v 1 and the glycoprotein STRUBBELIG. Unlike the situation in the moss , where one particular P4H was mainly responsible for the oxidation of erythropoietin, the tobacco P4Hs exhibited rather similar activities, albeit with biased substrate preferences and preferred sites of oxidation. From a biotechnological viewpoint, this result means that silencing/knockout of a single in cannot be expected to result in the abolishment of the plant-specific oxidation of prolyl residues in a recombinant protein.