Nicol S, Rahman D, Baines A J
Research School of Biosciences, University of Kent, Canterbury, Kent, CT2 7NJ, England.
Biochemistry. 1997 Sep 23;36(38):11487-95. doi: 10.1021/bi970709r.
The synapsins are a family of proteins associated with small synaptic vesicles that are implicated in synaptic maintenance and in the supply of vesicles for exocytosis. They are well characterized as substrates for protein kinases, and one class of synapsin, synapsin I, has been shown to bind, and be regulated by, calmodulin. A representative of the synapsin II class is now shown to bind calmodulin. Optical biosensor assays of Ca2+-dependent calmodulin binding to recombinant rat synapsin IIb indicated an apparent KD for calmodulin of 31 +/- 5 nM. Phosphorylation at Ser 10 increased the rates of calmodulin association (by a factor of 10) and dissociation (by a factor of 20). Fragment analysis and predictions from the sequence indicated two potential calmodulin binding sequences in the conserved central (C) domain. Peptides representing these sequences (residues 122-143 and 313-334 in synapsin IIb) were synthesized. Peptide 122-143 was found to bind calmodulin (KD 32 +/- 10 nM) and inhibit interaction of synapsin IIb with calmodulin. The interaction of peptide 313-334 was much weaker. Sequences similar to residues 122-143 are present in all published synapsin sequences. Calmodulin binding by synapsins seems not to be confined to mammals: a recombinant Drosophila synapsin 1 fragment containing part of the C-domain showed Ca2+-dependent binding to mammalian calmodulin. We conclude that calmodulin binding to synapsins is likely to be a general aspect of regulation of synaptic function.
突触素是一类与小突触囊泡相关的蛋白质家族，参与突触维持以及为胞吐作用提供囊泡。它们作为蛋白激酶的底物已得到充分表征，并且一类突触素，即突触素I，已被证明可与钙调蛋白结合并受其调节。现在已表明突触素II类的一个代表也能结合钙调蛋白。对重组大鼠突触素IIb与钙调蛋白的Ca2+依赖性结合进行的光学生物传感器分析表明，钙调蛋白的表观解离常数KD为31±5 nM。丝氨酸10位点的磷酸化增加了钙调蛋白结合（增加了10倍）和解离（增加了20倍）的速率。片段分析和序列预测表明，在保守的中央（C）结构域中有两个潜在的钙调蛋白结合序列。合成了代表这些序列的肽（突触素IIb中的122 - 143位和313 - 334位残基）。发现肽122 - 143能结合钙调蛋白（KD为32±10 nM）并抑制突触素IIb与钙调蛋白的相互作用。肽313 - 334的相互作用则弱得多。在所有已发表的突触素序列中都存在与122 - 143位残基相似的序列。突触素与钙调蛋白的结合似乎并不局限于哺乳动物：一个包含部分C结构域的重组果蝇突触素1片段显示出与哺乳动物钙调蛋白的Ca2+依赖性结合。我们得出结论，钙调蛋白与突触素的结合可能是突触功能调节的一个普遍方面。
