PDF(Pubmed)
Abstract：
Visceral myopathy is a life-threatening disease characterized by muscle weakness in the bowel, bladder, and uterus. Mutations in smooth muscle γ-actin (ACTG2) are the most common cause of the disease, but the mechanisms by which the mutations alter muscle function are unknown. Here, we examined four prevalent ACTG2 mutations (R40C, R148C, R178C, and R257C) that cause different disease severity and are spread throughout the actin fold. R178C displayed premature degradation, R148C disrupted interactions with actin-binding proteins, R40C inhibited polymerization, and R257C destabilized filaments. Because these mutations are heterozygous, we also analyzed 50/50 mixtures with wild-type (WT) ACTG2. The WT/R40C mixture impaired filament nucleation by leiomodin 1, and WT/R257C produced filaments that were easily fragmented by smooth muscle myosin. Smooth muscle tropomyosin isoform Tpm1.4 partially rescued the defects of R40C and R257C. Cryo-electron microscopy structures of filaments formed by R40C and R257C revealed disrupted intersubunit contacts. The biochemical and structural properties of the mutants correlate with their genotype-specific disease severity.
摘要：
内脏肌病是一种威胁生命的疾病，其特征是肠道肌肉无力，膀胱,还有子宫.平滑肌γ-肌动蛋白（ACTG2）的突变是该疾病的最常见原因，但是突变改变肌肉功能的机制尚不清楚。这里,我们检查了四种常见的ACTG2突变(R40C，R148C,R178C,和R257C）引起不同的疾病严重程度，并在整个肌动蛋白折叠中传播。R178C显示过早降解，R148C破坏与肌动蛋白结合蛋白的相互作用，R40C抑制聚合，和R257C去稳定的长丝。因为这些突变是杂合的,我们还分析了50/50与野生型(WT)ACTG2的混合物。WT/R40C混合物通过leiomoodin1损害了细丝成核，而WT/R257C产生的细丝很容易被平滑肌肌球蛋白片段化。平滑肌原肌球蛋白亚型Tpm1.4部分挽救了R40C和R257C的缺陷。由R40C和R257C形成的细丝的低温电子显微镜结构显示出破坏的亚基间接触。突变体的生化和结构特性与其基因型特异性疾病严重程度相关。
