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].