ABSTRACT
Recombinant deoxyribonucleic acid (DNA) technology has made it possible for genes to be introduced into different expression systems ranging from microorganisms (bacteria, fungi, yeast) (Georgiou, 1988) to insect cells (Luckow and Summers, 1988), plants (rice, potatoes, tobacco leaves) (Kusnadi et al., 1997), and transgenic animals (cows, pigs, sheep, goat) (Lubon et al., 1996). Different expression systems have been used to obtain high levels of human proteins for therapeutic use, such as tissue plasminogen activator (Gordon et al., 1992), α1-antitrypsin (Archibald et al., 1990), protein C (Velander et al., 1992), blood clotting factor VII (Niemann et al., 1999), and apolipoprotein C-II (Wang et al., 1996). Many proteins of pharmaceutical and/or commercial interest undergo complex posttranslational modifications that influence biological function. Therefore, not only should high-level protein expression be achieved by a specific system, but the system should also have the necessary machinery to produce correctly processed proteins when this is required. In addition, the choice of an expression system depends upon the amount of recombinant protein desired, cost-effectiveness, the time required for the isolation and purification of the recombinant protein, and its intended use. Current developments have focused on producing recombinant proteins that may be used as food ingredients. Expressing recombinant proteins in systems that introduce few or no contaminants to the final product or present little risk of an allergic response is paramount. Expression of bioactive recombinant proteins in edible plants that may be consumed uncooked, such as bananas or tomatoes, also offers an attractive delivery system.
