Rod Devenish; Week 5 MED1011; Biochemistry
To use proteins to treat disease cDNAs must be produced (lack introns so can be transcribed by prokaryotes), introduced into a gene into a host cell system where it is expressed, and host cells grown on a commercial scale. There must be purification of product to meet standards, extensive testing for efficacy and approval from authorities for clinical use. It turns cells into protein factories, and allows the cloned gene to be introduced into vectors for high level expression (protein production; called expression vectors) in host cells such as bacteria, yeast or cultured insect/mammalian cells. Bacteria and yeast are easier to grow. Mammalian cells are better at dealing with large proteins. For a vector carrying a gene of interest, the gene must be adjacent to appropriate sequences for its transcription and translation in the host cell, processing sequences for protein may also be included to facilitate purification/secretion.
Recombinant DNA and expression vectors have been used to produce medicaly useful proteins that may be difficult to usually obtain. tPA is being produced in E coli by recombinant techniques.
Growth hormone is species specific, derived from cadavers, Creutzfeld-Jacob was found so recombinant protein now made in bacteria or mammalian cells. Hep B has HBSAg surface protein which promotes antibody formation, succesfully synthesised in yeast.
DNA vaccines are based on use of plasmids containing protein coding genes, are not infectious or replicative, directly inject or fire DNA coated gold beads into muscle that contain antigen for body to develop a response against. Divide pathogen genome to look at plasmids to find out fragments that may confer protection (test on animals). Use these fragments for gene gun.
Transgenes can be used in food to confer useful elements/promote useful elements. There is concern about escape of transgenes into the environment. Transgenic animals can be used to produce useful products in their milk. Sheep can produce alpha-1-antitrypsin which hydrolyses connective tissue, excess elastase is found on the lungs of people with CF. Lack of alpha-glucosidase leads to Pompe's disease, alpha-glucosidase has been extracted from rabbits milk
siRNA can be used to treat disease from inappropriate gene expression, such as macular degeneration.