Proinsulin from Bacteria
One problem we face in the cloning and expression of a small hormone like insulin, is that the normal hormone is made in the pancreas through a series of precursors. Preproinsulin is a molecule some 100 amino acids long that has on its amino terminal end a hydrophobic presequence of 24 amino acids which is cleaved off as that molecule is passed through the cell membrane (1, 2). The resulting fragment, proinsulin, folds up; disulphide bonds form, and then a portion of the peptide chain, the C peptide, is cleaved out between two pairs of basic amino acid residues to produce the final molecule, insulin itself. When we make insulin in bacteria, we can do the final maturation ourselves with a mixture of trypsin and carboxypeptidase B. However, how can we arrange that the amino terminus will be the correct one for insulin rather than bearing some other amino acid or the presequence?
KeywordsLeader Sequence Periplasmic Space Tetracycline Resistance Basic Amino Acid Residue Ampicillin Resistance Gene
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