Yamaguchi K, Yamaguchi F, Miyamoto O, Sugimoto K, Konishi R, Hatase O, Tokuda M
Departments of Physiology, Faculty of Medicine, Kagawa Medical University, 1750-1 Ikenobe, Miki-cho, Kita-gun, Kagawa 761-0793, Japan.
J Biol Chem. 1999 Feb 5;274(6):3610-6. doi: 10.1074/jbc.274.6.3610.
A cDNA clone that encodes a novel Ca2+-binding protein was isolated from a human brain cDNA library. The gene for this clone, termed calbrain, encodes a 70-amino acid polypeptide with a predicted molecular mass of 8.06 kDa. The analysis of deduced amino acid sequence revealed that calbrain contains two putative EF-hand motifs that show significantly high homology to those of the calmodulin (CaM) family rather than two EF-hand protein families. By Northern hybridization analysis, an approximate 1.5-kilobase pair transcript of calbrain was detected exclusively in the brain, and in situ hybridization study revealed its abundant expression in the hippocampus, habenular area in the epithalamus, and in the cerebellum. A recombinant calbrain protein showed a Ca2+ binding capacity, suggesting the functional potency as a regulator of Ca2+-mediated cellular processes. Ca2+/calmodulin-dependent kinase II, the most abundant protein kinase in the hippocampus and strongly implicated in the basic neuronal functions, was used to evaluate the physiological roles of calbrain. Studies in vitro revealed that calbrain competitively inhibited CaM binding to Ca2+/calmodulin-dependent kinase II (Ki = 129 nM) and reduced its kinase activity and autophosphorylation.
从人脑cDNA文库中分离出一个编码新型钙结合蛋白的cDNA克隆。该克隆的基因称为钙脑蛋白，编码一个由70个氨基酸组成的多肽，预测分子量为8.06 kDa。对推导的氨基酸序列分析表明，钙脑蛋白含有两个假定的EF-手基序，与钙调蛋白（CaM）家族的基序具有显著的高度同源性，而不是两个EF-手蛋白家族。通过Northern杂交分析，仅在脑中检测到约1.5千碱基对的钙脑蛋白转录本，原位杂交研究显示其在海马体、上丘脑缰核区域和小脑中大量表达。重组钙脑蛋白显示出钙结合能力，表明其作为钙介导的细胞过程调节剂的功能效力。钙/钙调蛋白依赖性激酶II是海马体中最丰富的蛋白激酶，与基本神经元功能密切相关，被用于评估钙脑蛋白的生理作用。体外研究表明，钙脑蛋白竞争性抑制CaM与钙/钙调蛋白依赖性激酶II的结合（Ki = 129 nM），并降低其激酶活性和自身磷酸化。
