Cell and Molecular Studies

Active site of insulin-degrading enzyme (IDE)

Active site of IDE and surrounding residues implicated in the thiol sensitivity of the protease.

Source: Neant-Fery M, et al. Molecular basis for the thiol sensitivity of insulin-degrading enzyme. Proceedings of the National Academy of Sciences of the United States of America. 2008;105:9582.

More often than not, the identification of novel therapeutic targets is simply the starting point for elucidating their precise role in disease pathogenesis. The laboratory of Malcolm A. Leissring, Ph.D., is actively pursuing a number of projects — focused principally on the amyloid-beta-degrading protease, insulin-degrading enzyme (IDE) — that rely upon state-of-the-art molecular and cellular techniques.

As an example of the range of these projects, one recently completed project was related to the molecular basis for the thiol sensitivity of IDE.

The proteolytic activity of IDE is irreversibly inhibited by compounds that target the sulfhydryl moiety within cysteines. The latter compounds include several molecules produced by oxidative stress in the brain, such as 4-hydroxynonenal, a product of lipid peroxidation. So, the alkylation of cysteines within IDE could represent a key molecular link between oxidative damage and Alzheimer's disease pathogenesis.

The exact molecular mechanism underlying IDE's vulnerability to this class of compounds, though, was unknown. Also contributing to the complexity of the problem was that IDE contains 13 cysteines. Dr. Leissring's lab recently used site-directed mutagenesis to elucidate the specific cysteines within IDE that mediate this effect (see figure).

This work resolved a key question about IDE enzymology that had remained outstanding for more than half a century. The insights derived from this work may help to develop improved therapies based on engineered forms of IDE.