Influence of oxidation on the susceptibility of purified desmin to degradation by μ-calpain, caspase-3 and -6

This study was designed to investigate the effects of desmin oxidation on its degradation by proteolytic enzymes. Desmin was isolated from bovine muscle and exposed to varying oxidative conditions, and then incubated with μ-calpain, caspase-3 or -6, respectively. The extent of protein degradation was subsequently determined using SDS–PAGE and Western-blotting. Furthermore, the oxidative modification of the secondary structure of desmin was measured by circular dichroism (CD). Our results revealed that, compared with the native desmin, degradation of oxidised desmin was enhanced by caspases, but suppressed by μ-calpain. The CD spectra of desmin showed that the content of α-helix decreased from 76.2% to 52% while random coil increased from 8% to 22.4% after oxidation. These findings demonstrated that oxidative modifications of desmin changed their susceptibility to μ-calpain, caspase-3 and -6 as well as their secondary structure.