FTIR analysis of the high pressure response of native insulin assemblies

• Spectroscopic study of insulin under pressure in water solution and dry powder.
• Covalent/non-covalent bonds in globular structure make insulin resistant to pressure.
• We probed the stability of protein aggregates under compression.
• We investigated the role of water in destabilizing insulin assemblies.
• Pressure effects critically depend on the hierarchical organization of monomers.

It is widely recognized that a central role in conferring stability to the structure of proteins against misfolding and aggregation is played by the formation of oligomers. The case of insulin is prototypical in this respect: in our body it is stored up in stable inactive hexameric assemblies whereas only in its monomeric form it recovers the role of regulating carbohydrate and fat metabolism. In the present paper, exploiting the optimal coupling between FTIR spectroscopy and diamond anvil cell technique, we probe the stability of different insulin oligomeric forms under high pressure, namely over the ranges 0–15 kbar for water solution and 0–80 kbar for dry powder. Results obtained show different responses to volume compression for the different assemblies being the structure of monomers and dimers remarkably more affected by compression than hexamers. Moreover by comparing the results obtained using water solution and dry powder we were able to draw important considerations about the role of water in the high pressure unfolding processes.

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