Clancy C E, Mendoza M G, Naismith T V, Kolman M F, Egelhoff T T
Department of Physiology and Biophysics, Case Western Reserve School of Medicine, Cleveland, Ohio 44106-4970, USA.
J Biol Chem. 1997 May 2;272(18):11812-5. doi: 10.1074/jbc.272.18.11812.
Myosin II assembly and localization into the cytoskeleton is regulated by heavy chain phosphorylation in Dictyostelium. The enzyme myosin heavy chain kinase A (MHCK A) has been shown previously to drive myosin filament disassembly in vitro and in vivo. MHCK A is noteworthy in that its catalytic domain is unrelated to the conventional families of eukaryotic protein kinases. We report here the cloning and initial biochemical characterization of another kinase from Dictyostelium that is related to MHCK A. When the segment of this protein that is similar to the MHCK A catalytic domain was expressed in bacteria, the resultant protein displayed efficient autophosphorylation, phosphorylated Dictyostelium myosin II, and also phosphorylated a peptide substrate corresponding to a portion of the myosin II tail. We have therefore named this gene myosin heavy chain kinase B. These results provide the first confirmation that sequences in other proteins that are related to the MHCK A catalytic domain can also encode protein kinase activity. It is likely that the related segments of homology present in rat eukaryotic elongation factor-2 kinase and a putative nematode eukaryotic elongation factor-2 kinase also encode the catalytic domains of those enzymes.
在盘基网柄菌中，肌球蛋白II装配到细胞骨架并在其中定位受重链磷酸化调控。肌球蛋白重链激酶A（MHCK A）此前已被证明在体外和体内均可驱动肌球蛋白丝的解聚。MHCK A值得注意之处在于其催化结构域与真核蛋白激酶的传统家族无关。我们在此报告盘基网柄菌中另一种与MHCK A相关的激酶的克隆及初步生化特性。当该蛋白与MHCK A催化结构域相似的片段在细菌中表达时，产生的蛋白表现出高效的自磷酸化，能磷酸化盘基网柄菌肌球蛋白II，还能磷酸化对应肌球蛋白II尾部一部分的肽底物。因此，我们将该基因命名为肌球蛋白重链激酶B。这些结果首次证实，与MHCK A催化结构域相关的其他蛋白中的序列也可编码蛋白激酶活性。大鼠真核延伸因子2激酶和一种假定的线虫真核延伸因子2激酶中存在的相关同源片段可能也编码这些酶的催化结构域。
