Côté G P, Luo X, Murphy M B, Egelhoff T T
Department of Biochemistry, Queen's University, Kingston, Ontario K7L 3N6, Canada.
J Biol Chem. 1997 Mar 14;272(11):6846-9. doi: 10.1074/jbc.272.11.6846.
Myosin heavy chain kinase A (MHCK A) in Dictyostelium was identified as a biochemical activity that phosphorylates threonine residues in the myosin II tail domain and regulates myosin filament assembly. The catalytic domain of MHCK A has now been mapped through the functional characterization of a series of MHCK A truncation mutants expressed in Escherichia coli. A recombinant protein comprising the central nonrepetitive domain of MHCK A (residues 552-841) was isolated in a soluble form and shown to phosphorylate Dictyostelium myosin II, myelin basic protein, and a synthetic peptide substrate. The functionally mapped catalytic domain of MHCK A shows no detectable sequence similarity to known classes of eukaryotic protein kinases but shares substantial sequence similarity with a transcribed Caenorhabditis elegans gene and with the mammalian elongation factor-2 kinase (calcium/calmodulin-dependent protein kinase III). We suggest that MHCK A represents the prototype for a novel, widely occurring protein kinase family.
盘基网柄菌中的肌球蛋白重链激酶A（MHCK A）被鉴定为一种生化活性物质，它能使肌球蛋白II尾部结构域中的苏氨酸残基磷酸化，并调节肌球蛋白丝的组装。现在，通过对一系列在大肠杆菌中表达的MHCK A截短突变体进行功能表征，已确定了MHCK A的催化结构域。一种包含MHCK A中央非重复结构域（第552 - 841位氨基酸残基）的重组蛋白以可溶形式分离出来，并显示出能使盘基网柄菌肌球蛋白II、髓鞘碱性蛋白和一种合成肽底物磷酸化。功能定位的MHCK A催化结构域与已知的真核蛋白激酶类别没有可检测到的序列相似性，但与秀丽隐杆线虫的一个转录基因以及哺乳动物延伸因子2激酶（钙/钙调蛋白依赖性蛋白激酶III）有大量的序列相似性。我们认为，MHCK A代表了一个新的、广泛存在的蛋白激酶家族的原型。
