蛋白质磷酸化对肌动球蛋白解离及其乙酰化水平的影响

Effects of Protein Phosphorylation on the Dissociation and Acetylation Level of Actomyosin

【目的】研究肌球蛋白重链和肌动蛋白磷酸化对其乙酰化水平、肌动球蛋白解离及ATP酶活性的影响,为通过调控磷酸化水平改善肉品嫩度提供理论依据。【方法】以羊背最长肌为材料制备肌肉匀浆液,采用碱性磷酸酶抑制剂(抑制去磷酸化)和蛋白激酶抑制剂(抑制磷酸化)调控其磷酸化水平,在4℃分别孵育0、0.5、4、12、24、48和72 h,利用SDS-PAGE电泳和荧光染色、蛋白质免疫印迹、ATP酶活性测定试剂盒分析蛋白质磷酸化水平、乙酰化水平、肌动球蛋白解离程度和ATP酶活性随孵育时间的变化;利用分子动力学模拟分析肌球蛋白重链和肌动蛋白磷酸化对肌动球蛋白结构的影响。【结果】碱性磷酸酶抑制剂处理组中肌球蛋白重链磷酸化水平在孵育4、12和72 h时显著高于对照组和蛋白激酶抑制处理组(P<0.05),肌动蛋白磷酸化水平在孵育4、12、24、48和72 h时显著高于对照组和蛋白激酶抑制处理组(P<0.05),表明肌球蛋白重链和肌动蛋白发生去磷酸化反应被碱性磷酸酶抑制剂所抑制。碱性磷酸酶抑制剂处理组中肌动蛋白乙酰化水平在孵育4、12、24、48和72 h时显著低于蛋白激酶抑制组(P<0.05),肌球蛋白重链乙酰化水平呈无规律变化,表明肌动蛋白磷酸化抑制其乙酰化,肌球蛋白重链磷酸化对其乙酰化影响无明显规律。分子动力学结果表明,肌球蛋白重链第2、3、54位丝氨酸等位点和肌动蛋白第54位丝氨酸、第55位酪氨酸等位点磷酸化增加了肌动球蛋白结构的总能量、势能和动能,降低了键能,导致肌动球蛋白结构变得不稳定。在0—72 h孵育过程中,碱性磷酸酶抑制剂处理组的肌动球蛋白解离程度始终高于蛋白激酶抑制处理组,ATP酶活性低于蛋白激酶抑制处理组(P<0.05),表明肌球蛋白重链和肌动蛋白磷酸化促进肌动球蛋白解离。【结论】肌球蛋白重链磷酸化直接促进肌动球蛋白解离,肌动蛋白磷酸化通过抑制其自身乙酰化促进肌动球蛋白解离。

【Objective】The objective of this study was to investigate the effects of myosin heavy chain and actin phosphorylation on their acetylation levels, actomyosin dissociation, and ATPase activity, so as to provide a theoretical basis for improving meat tenderness by regulating protein phosphorylation level.【Method】The homogenate of sheep longissimus dorsi muscle was incubated with alkaline phosphatase inhibitor(inhibiting dephosphorylation) and protein kinase inhibitor(inhibiting phosphorylation) at 4℃ for 0, 0.5, 4, 12, 24, 48, and 72 h to regulate the phosphorylation levels of myosin heavy chain and actin.The protein phosphorylation level was measured by SDS-PAGE and fluorescent staining, and the acetylation level and actomyosin dissociation degree were measured by Western blotting. The ATPase activity was measured using an assay kit. The influence of myosin heavy chain and actin phosphorylation on the structure of actomyosin was analyzed by molecular dynamics simulation.【Result】The phosphorylation level of myosin heavy chain in the alkaline phosphatase inhibitor treatment group was significantly higher than that in the control and protein kinase inhibitor treatment groups at 4, 12, and 72 h of incubation(P<0.05). The phosphorylation level of actin was significantly higher than that in the control and protein kinase inhibition treatment groups at 4, 12, 24, 48, and 72 h of incubation(P<0.05), which indicated that alkaline phosphatase inhibitors could inhibit the dephosphorylation of myosin heavy chain and actin during incubation in vitro. The acetylation level of actin in the alkaline phosphatase inhibitor treatment group was significantly lower than that in the protein kinase inhibitor treatment group after incubation for 4, 12, 24, 48, and 72 h(P<0.05), while the acetylation level of myosin heavy chain changed irregularly. The results indicated that the phosphorylation of actin inhibited its acetylation, while the phosphorylation of myosin heavy chain had no obvious regularity on its acetylation. The results of molecular dynamics showed that the phosphorylation of the 2nd, 3rd and 54th serine positions of the myosin heavy chain and the 54th and 55th tyrosine positions of actin increased the total energy,potential energy, and kinetic energy of actomyosin. However, the bond energy of actomyosin was reduced, which caused the unstable structure of actomyosin. The dissociation degree of actomyosin in the alkaline phosphatase inhibitor treatment group was always higher than that of the protein kinase inhibitor treatment group during 0-72 h incubation(P<0.05). The ATPase activity was always lower than that in the protein kinase inhibitor treatment group during 0-72 h incubation(P<0.05). The myosin heavy chain and actin phosphorylation promoted actomyosin dissociation.【Conclusion】The phosphorylation of myosin heavy chain directly promoted the dissociation of actomyosin, while the phosphorylation of actin promoted the dissociation of actomyosin by inhibiting its acetylation.