Eddington Casey, Titus Margaret A
Department of Genetics, Cell Biology, and Development, University of Minnesota, Minneapolis, Minnesota, USA; Graduate Program in Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, Minnesota, USA.
Department of Genetics, Cell Biology, and Development, University of Minnesota, Minneapolis, Minnesota, USA; Graduate Program in Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, Minnesota, USA.
J Biol Chem. 2025 May;301(5):108371. doi: 10.1016/j.jbc.2025.108371. Epub 2025 Mar 3.
MyTH4-FERM (MF) myosins are a family of molecular motors with critical roles in the formation and organization of thin membrane protrusions supported by parallel bundles of actin - filopodia, microvilli, and stereocilia. The amoeboid MF myosin DdMyo7 is essential for filopodia formation but its mechanism of action is unknown. The motor properties of a forced-dimer of the DdMyo7 motor were characterized using an in vitro motility assay to address this question. The DdMyo7 motor associates with two different light chains, the Dictyostelium calmodulins CalA and CalB, whose binding is shown to be sensitive to the presence of calcium. Total internal reflection fluorescence motility assays of the dimerized DdMyo7 motor reveal that it is a slow, processive motor that moves along actin at ∼ 40 nm/sec, and the activity of the motor is significantly reduced in the presence of Ca. The speed of DdMyo7 is similar to that of other Myo7 family members such as human Myo7A and fly DmMyo7A, but is at least 10-fold slower than the mammalian filopodial MF myosin, Myo10. The results show that evolutionarily distant native filopodial myosins can promote filopodia elongation using motors with distinct properties, revealing diverse mechanisms of myosin-based filopodia formation.
MyTH4-FERM（MF）肌球蛋白是一类分子马达，在由平行肌动蛋白束支撑的薄细胞膜突起（丝状伪足、微绒毛和静纤毛）的形成和组织中起关键作用。变形虫MF肌球蛋白DdMyo7对丝状伪足的形成至关重要，但其作用机制尚不清楚。为了解决这个问题，使用体外运动分析对DdMyo7马达的强制二聚体的运动特性进行了表征。DdMyo7马达与两种不同的轻链（盘基网柄菌钙调蛋白CalA和CalB）结合，其结合显示对钙的存在敏感。二聚化DdMyo7马达的全内反射荧光运动分析表明，它是一种缓慢、持续运动的马达，以约40nm/秒的速度沿着肌动蛋白移动，并且在有钙的情况下马达的活性显著降低。DdMyo7的速度与其他Myo7家族成员（如人类Myo7A和果蝇DmMyo7A）相似，但比哺乳动物丝状伪足MF肌球蛋白Myo10至少慢10倍。结果表明，进化上距离较远的天然丝状伪足肌球蛋白可以使用具有不同特性的马达促进丝状伪足伸长，揭示了基于肌球蛋白的丝状伪足形成的多种机制。
