Modern Industrial Microbiology and Biotechnology

Screening for Productive Strains and Strain Improvement 157Top: Structure of insulin. The A chain has 21 amino acids (represented by circles) and the B chain has 30amino acids. The A and B chains are linked by disulfide bond between cysteine residues (filled circles)Bottom: Synthesis of Insulin: Proinsulin, the Precursor of InsulinWhen synthesized proinsulin consists of an 81-amino acid polypeptide. The C chain is then cleaved off bya protease (P) to yield insulin.Fig. 7.13Structure and Synthesis of Insulinimmune responses represent a first line of defense against most pathogens. In contrast,mucosally targeted vaccines achieve stimulation of both the systemic as well as themucosal immune networks. In addition, mucosal vaccines delivered orally increasesafety and compliance by eliminating the need for needles. In addition many vaccinesdepend on the need of maintenance of a ‘cold chain’ (refrigeration) for delivery. Manydeveloping countries, lack the resources to maintain the chain giving rise to many casesof vaccine failure, along with the fact they lack the resources and technology forfermentation industries. Both of these factors create constraints in vaccine use in thedeveloping world, where these vaccines are needed the most. Combining a cost-effectiveproduction system with a safe and efficacious delivery system, plant edible vaccines,provide a compelling new opportunity.Plant-based oral vaccines are cheap, safe and efficient. From the point of the little childreceiving the vaccine, a smile might be elicited when a ‘banana’ vaccine is eaten ratherthe sharp cry of the pain of a needle! Vaccines have been produced in several plants,including a vaccine against dental carries caused by Streptococcus mutans, which wasproduced in the tobacco. Two other interesting examples are the expression of the rabiesexternal antigen in tomatoes and the hepatitis virus antigen in lettuce.7.2.2.2.8.10 Genetically engineered plantsPlants have been engineered for the introduction of many new desirable properties.Collectively these attainments represent a major triumph of biotechnology, enabling us to