| Transgenic corn is capable of producing and storing Type I alpha1 human collagen (r-CIalpha1) containing a sequence that assists assembly (foldon) and the mature cleaved form (without foldon). Extracts of ground corn grain spiked with Pichia-sourced collagen (rP-CIalpha1), with and without foldon, were precipitated with NaCl to purify collagen from host cell proteins. The low acid solubility of host cell proteins (HCP's) along with the acid stability of collagen favored extraction at pH 2. NaCl concentrations >0.75 M provided complete precipitation of rP-CIalpha1 without foldon and >70% purity. A fractional cut to remove HCP.s with 0.25 M NaCl and precipitation of rP-CIalpha1 with 1.0 M NaCl increased the purity to 95% at the expense of yield. The presence of foldon negatively impacted yield and purity results, 94% and 44% respectively, and these did not improve with increased NaCl concentration. Pepsin added to cleave foldon and host cell proteins prior to precipitation had no effect on yield or purity. Cleavage after precipitation reduced the volume to be treated with pepsin , and subsequent reprecipitation of the partially converted rP-CIalpha1 improved purity to 67%. The purity of rP-CIalpha1 with foldon recovered from Pichia extracts was lower (16.8%) than when recovered from corn extracts, but maintained yield >90% and foldon content of approximately 60%. |
