Wang Fei, Kovacs Mihaly, Hu Aihua, Limouze John, Harvey Estelle V, Sellers James R
Laboratory of Molecular Cardiology, NHLBI, National Institutes of Health, Bethesda, Maryland 20892-1762, USA.
J Biol Chem. 2003 Jul 25;278(30):27439-48. doi: 10.1074/jbc.M302510200. Epub 2003 Apr 17.
Besides driving contraction of various types of muscle tissue, conventional (class II) myosins serve essential cellular functions and are ubiquitously expressed in eukaryotic cells. Three different isoforms in the human myosin complement have been identified as non-muscle class II myosins. Here we report the kinetic characterization of a human non-muscle myosin IIB subfragment-1 construct produced in the baculovirus expression system. Transient kinetic data show that most steps of the actomyosin ATPase cycle are slowed down compared with other class II myosins. The ADP affinity of subfragment-1 is unusually high even in the presence of actin filaments, and the rate of ADP release is close to the steady-state ATPase rate. Thus, non-muscle myosin IIB subfragment-1 spends a significantly higher proportion of its kinetic cycle strongly attached to actin than do the muscle myosins. This feature is even more pronounced at slightly elevated ADP levels, and it may be important in carrying out the cellular functions of this isoform working in small filamentous assemblies.
除了驱动各种类型的肌肉组织收缩外，传统的（II类）肌球蛋白还发挥着重要的细胞功能，并且在真核细胞中普遍表达。人类肌球蛋白复合物中的三种不同亚型已被鉴定为非肌肉II类肌球蛋白。在此，我们报告了在杆状病毒表达系统中产生的人类非肌肉肌球蛋白IIB亚片段-1构建体的动力学特征。瞬态动力学数据表明，与其他II类肌球蛋白相比，肌动球蛋白ATP酶循环的大多数步骤都减慢了。即使在存在肌动蛋白丝的情况下，亚片段-1对ADP的亲和力也异常高，并且ADP释放速率接近稳态ATP酶速率。因此，与肌肉肌球蛋白相比，非肌肉肌球蛋白IIB亚片段-1在其动力学循环中与肌动蛋白紧密结合的比例要高得多。这一特征在ADP水平略有升高时更为明显，并且对于在小丝状组装体中发挥作用的这种亚型的细胞功能可能很重要。
