Collagens require the hydroxylation of proline (Pro) residues in their triple-helical domain repeating sequence Xaa-Pro-Gly to function properly as a main structural component of the extracellular matrix in animals at physiologically relevant conditions.
The regioselective proline hydroxylation is catalyzed by a specific prolyl 4-hydroxylase (P4H) as a posttranslational processing step.
Results
A recombinant human collagen type I alpha-1 (rCIalpha1) with high percentage of hydroxylated prolines (Hyp) was produced in transgenic maize seeds when co-expressed with both the alpha- and beta- subunits of a recombinant human P4H (rP4H). Germ-specific expression of rCIalpha1 using maize globulin-1 gene promoter resulted in an average yield of 12 mg/kg seed for the full-length rCIalpha1 in seeds without co-expression of rP4H and 4 mg/kg seed for the rCIalpha1 (rCIalpha1-OH) in seeds with co-expression of rP4H. High-resolution mass spectrometry (HRMS) analysis revealed that nearly half of the collagenous repeating triplets in rCIalpha1 isolated from rP4H co-expressing maize line had the Pro residues changed to Hyp residues. The HRMS analysis determined the Hyp content of maize-derived rCIalpha1-OH as 18.11%, which is comparable to the Hyp level of yeast-derived rCIalpha1-OH (17.47%) and the native human CIa1 (14.59%), respectively. The increased Hyp percentage was correlated with a markedly enhanced thermal stability of maize-derived rCIalpha1-OH when compared to the non-hydroxylated rCIalpha1.
Conclusions
This work shows that maize has potential to produce adequately modified exogenous proteins with mammalian-like post-translational modifications that may be require for their use as pharmaceutical and industrial products.
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