Post-translational Modification of preproinsulin to biologically-active insulin

         Preproinsulin is initially translated as a 110 amino acid molecule, comprising a signal peptide and B-, C- & A-chains. The signal peptide (24 aa's) is first clipped from amino terminus. The A- & B- Chains of the proinsulin are then joined by disulfide bridges. This stabilizes the molecule so that the intervening C peptide (35 aa's) can be excised. The biologically-active, tertiary structure of insulin comprises an A chain (30 aa's) & B chain (21 aa's) held together by 3 disulfide bridges. [One S-S bridge that joins two cys residues in the A-Chain is not shown].

Figure ©2012 TA Brown, Introduction to Genetics (1st ed.); additional text ©2014 by Steven M. Carr