Synergistic action of cathepsin B, L, D and calpain in disassembly and degradation of myofibrillar protein of grass carp.

The objective of this study was to investigate the differential role of cathepsin B, L, D and calpain in degradation and disassembly of myofilament. Myofibrillar protein of grass carp (Ctenopharyngodon idella) was incubated with proteases monotonously, simultaneously or sequentially. Subsequently, protein degradation were detected using SDS-PAGE and myofilament disassembly induced by changes of non-covalent interactions were measured through SDS-PAGE using l-Ethyl-3-(3-Dimethylaminopropyl) Carbodiimide (EDC) as a zero length cross-linker. Additionally, content of heat shock proteins which functioned in stabilizing assembly architecture of myofibrillar protein was determined. Results showed that calpain and cathepsin B, calpain and cathepisn L could act in a stepwise and complimentary manner to synergistically dissociate and degrade myofibrillar protein. In synergistic action, cathepsin B disrupted the thick filament assembly through lowering the UNC45 and HSP90 concentration in myofibrillar protein, facilitating the degradation of dissociated MHC by calpain. Meanwhile, Cathepsin L was shown to preferentially remove the actin from thin filament via lowering the content of HSP27 and αb-crystallin, to create dissociated actin as substrate supply for calpain.