Effect of the combined action of myofibrillar protein phosphorylation and S-nitrosylation on the degradation of myofibrillar proteins by µ-calpain

This study investigated the responsiveness of interactively phosphorylated and S-nitrosylated myofibrillar proteins (MPs) to µ-calpain for elucidating the interactive effect of phosphorylation and S-nitrosylation on MPs degradation. MP were treated with protein kinase A (PKA), S-nitrosoglutathione (SNG) and PKA + SNG, respectively, to regulate its modification levels, and then incubated with µ-calpain for 40 min. The results showed that phosphorylation level of MPs significantly raised in PKA and PKA + SNG group (p < 0.05), but presented insignificantly differences between these two groups (p ≥ 0.05). S-nitrosylation level of MPs was significantly higher in PKA + SNG group than that in other groups (p < 0.05). MPs co-modified by phosphorylation and S-nitrosylation significantly promoted the degradation of actin (p < 0.05), but inhibited the degradation of desmin. Besides, both co-modification or single modification of MPs showed little influence on the degradation of myosin heavy chain by µ-calpain. The crosstalk of phosphorylation and S-nitrosylation of MPs plays different roles in regulating the degradation of different types of MPs via µ-calpain.