Recovering corn germ enriched in recombinant protein by wet-fractionation

Abstract

Corn wet-fractionation processes (quick-germ fractionation and traditional wet milling) were evaluated as means of recovering fractions rich in recombinant collagen-related proteins that were targeted for expression in the germ (embryo) of transgenic corn. Transgenic corn lines accumulating a recombinant full-length human collagen type-I-alpha-1 (full-length rCIα1) or a 44-kDa rCIα1 fragment targeted for seed expression with an embryo-specific promoter were used. Factors to consider in efficient recovery processes are the distribution of the peptides among botanical parts and process recovery efficiency. Both recombinant proteins were distributed 62–64% in germ comprising about 8.6% of the dry grain mass; 34–38% in the endosperm comprising 84% of the dry grain mass; 1.7% in the pericarp comprising about 5% of the dry mass; and 1% in the tip-cap comprising 1.5–2% of the dry mass. The quick-germ method employed a short steeping period either in water or SO 2–lactic acid solution followed by wet-milling degermination to recover a germ-rich fraction. Of the total recombinant protein expressed in germ, the quick-germ process recovered 40–43% of the total recombinant protein within 6–8% of the corn mass. The traditional corn wet-milling process produced higher purity germ but with lower recovery (24–26%) of the recombinant protein. The two quick-germ methods, using water alone or SO 2–lactic acid steeping, did not substantially differ in rCIα1 recovery, and the quick-germ processes recovered germ with less leaching and proteolytic losses of the recombinant proteins than did traditional wet milling. Thus, grain fractionation enriched the recombinant proteins 6-fold higher than that of unfractionated kernels. Such enrichment may improve downstream processing efficiency and enable utilizing the protein-lean co-products to produce biofuels and biorenewable chemicals by fermenting the remaining starch-rich fractions.