The effect of pH on the conformational stability of insulin was studied. Surprisingly, the Gibbs free energy of unfolding increased approximately 30% by acidification. pH titration of insulin's conformational stability is described by a transition involving a single proton with an apparent pK(a) of 7.0. The acid stabilization of insulin's conformation was attributed to the protonation of histidine at position 5 on the B-chain (HB5) as determined by 1H-NMR of the histidines, selective amino acid alteration, and enthalpies of ionization. Further acidification (at least to pH 2) does not decrease the free energy of unfolding. A conformational change in the tertiary structure, as indicated by the near-UV circular dichroism spectrum, accompanies this change in stability. We propose that this acid stabilization of insulin is physiologically important in maintaining insulin stability in the acid environment of the secretory/storage granules of the beta-cell of the pancreatic islets of Langerhans. Study holds ProTherm entries: 4550, 4551, 4552, 4553, 4554 Extra Details: additive : EDTA(1 mM), acidification; transition; protonation; conformational change;,tertiary structure
Submitter: Connie Wang
Submission Date: April 24, 2018, 8:26 p.m.
|Number of data points||5|
|Proteins||Insulin ; Insulin|
|Assays/Quantities/Protocols||Experimental Assay: dG pH:6.0 ; Experimental Assay: dG pH:8.0 ; Experimental Assay: dG pH:2.0|
|Libraries||Mutations for sequence A:GIVEQCCTSICSLYQLENYCN/B:FVNQHLCGSHLVEALYLVCGERGFFYTPKT/C:GIVEQCCTSICSLYQLENYCN/D:FVNQHLCGSHLVEALYLVCGERGFFYTPKT/E:GIVEQCCTSICSLYQLENYCN/F:FVNQHLCGSHLVEALYLVCGERGFFYTPKT/G:GIVEQCCTSICSLYQLENYCN/H:FVNQHLCGSHLVEALYLVCGERGFFYTPKT/I:GIVEQCCTSICSLYQLENYCN/J:FVNQHLCGSHLVEALYLVCGERGFFYTPKT/K:GIVEQCCTSICSLYQLENYCN/L:FVNQHLCGSHLVEALYLVCGERGFFYTPKT|