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Hoffmann, R. A wiki for the life sciences where authorship matters. Nature Genetics (2008)

The insulin receptor substrate ( IRS-1) is a PEST protein that is susceptible to calpain degradation in vitro.

The insulin receptor substrate 1 ( IRS-1) contains at least 11 sequence motifs that are rich in proline ( P), glutamic acid (E), serine ( S), and threonine ( T), i.e., PEST regions. Proteins with PEST regions turn over rapidly. IRS-1 is degraded rapidly in vivo upon exposure of 3T3-L1 adipocytes to insulin. The intracellular, calcium-dependent, neutral proteases known as calpains are one possible mechanism by which IRS-1 may be degraded. To begin to investigate this possibility, purified exogenous calpain was shown to degrade IRS-1 in cell-free extracts from basal and insulin-treated cells and rat recombinant IRS-1 in vitro. Only two proteolytic fragments could be detected. One had a mol wt of approximately 79 kDa, arising from the C-terminus end, and the second had a mol wt of approximately 90 kDa arising from near the N-terminus, possibly a product of the same cleavage event, since the mol wt of IRS-1 from insulin-treated cells was approximately 170 kDa. These results suggest that IRS-1 may serve as a substrate for calpain in vivo, accounting for its rapid degradation.[1]


  1. The insulin receptor substrate (IRS-1) is a PEST protein that is susceptible to calpain degradation in vitro. Smith, L.K., Bradshaw, M., Croall, D.E., Garner, C.W. Biochem. Biophys. Res. Commun. (1993) [Pubmed]
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