Purification and characterization of a transgenic corn grain‐derived recombinant collagen type I alpha 1

Corn offers advantages as a transgenic host for producing recombinant proteins required at large volumes (1,000's of tons per year) and low cost (less than US$50/kg) by generating them as co‐products of biorefining. We describe the purification and characterization of a corn grain‐derived mammalian structural protein having such market characteristics: a full length recombinant collagen type I alpha 1 (rCIα1) chain. Material properties of interest are gelation behavior, which would depend on as yet unverified ability of corn to carry out post‐translational prolyl hydroxylation and formation of triple helical conformation. The starting material was grain where the expression of rCIα1 had been directed by an embryo‐specific promoter. Purification consisted of extraction at low pH followed by membrane and chromatographic steps to isolate rCIα1 for characterization. The amino acid composition and immunoreactivity of CIα1 was similar to that of an analogous native human CIα1 and to rCIα1 produced by the yeast Pichia pastoris. Tandem mass spectrometry confirmed the primary sequence of the corn‐derived rCIα1 with 46% coverage. Fragments of the rCIα1chains were also observed, possibly caused by endogenous plant proteases. The corn‐derived rCIα1 had a low level of prolyl hydroxylation (～1% versus 11%) relative to animal‐derived CIα1 and folded into its characteristic triple‐helical structure as indicated by its resistance to pepsin digestion below its melting temperature of 26^oC. The 29 amino acid foldon fused to the C‐terminus to initiate triple helix formation was not cleaved from the rCIα1chains, but could be removed by pepsin treatment. © 2009 American Institute of Chemical Engineers Biotechnol. Prog. 2009