Insulin-degrading enzyme (IDE), a ubiquitously expressed
zinc metalloprotease, has multiple activities in addition to
insulin degradation and its malfunction is believed to connect
type 2 diabetes with
Alzheimer's disease. IDE has been found in many different cellular compartments, where it may experience significant physio-pathological pH variations. However, the exact role of pH variations on the interplay between
enzyme conformations, stability, oligomerization state and catalysis is not understood. Here, we use ESI mass spectrometry, atomic force microscopy, surface plasmon resonance and circular dichroism to investigate the structure-activity relationship of IDE at different pH values. We show that acidic pH affects the ability of the
enzyme to bind the substrate and decrease the stability of the
protein by inducing an α-helical bundle conformation with a concomitant dissociation of multi-subunit IDE assemblies into monomeric units and loss of activity. These effects suggest a major role played by electrostatic forces in regulating multi-subunit
enzyme assembly and function. Our results clearly indicate a pH dependent coupling among
enzyme conformation, assembly and stability and suggest that cellular
acidosis can have a large effect on IDE oligomerization state, inducing an
enzyme inactivation and an altered
insulin degradation that could have an impact on
insulin signaling.