Bozóky Zoltán, Alexa Anita, Tompa Peter, Friedrich Peter
Institute of Enzymology, Biological Research Center, Hungarian Academy of Sciences, P.O. Box 7, 1518 Budapest, Hungary.
Biochem J. 2005 Jun 15;388(Pt 3):741-4. doi: 10.1042/BJ20041935.
Typical calpains in mammals become activated on binding of 8-12 Ca2+ ions per enzyme molecule, giving an example of integrated, manifold regulation by calcium. Besides two identified Ca2+ sites in catalytic domain II and several EF-hand motifs in domains IV and VI, an acidic loop in the centrally positioned domain III seems to harbour Ca2+. The mediator of distant Ca2+-induced structural transitions is an elongated structural element, the 'transducer'. By site-directed mutagenesis along the transducer, we have generated various forms of rat m-calpain in which critical intramolecular interactions, as judged from the X-ray structure, would be abolished or modified. The kinetic parameters of these mutant enzymes support a model featuring shrinkage of transducer as a contributor to structural changes involved in calpain activation.
哺乳动物中的典型钙蛋白酶在每个酶分子结合8 - 12个Ca2+离子时被激活，这是钙对其进行整合、多方面调控的一个例子。除了在催化结构域II中已确定的两个Ca2+位点以及结构域IV和VI中的几个EF手基序外，位于中央的结构域III中的一个酸性环似乎也含有Ca2+。远距离Ca2+诱导的结构转变的介质是一个细长的结构元件，即“传感器”。通过沿传感器进行定点诱变，我们产生了多种形式的大鼠m-钙蛋白酶，根据X射线结构判断，其中关键的分子内相互作用将被消除或改变。这些突变酶的动力学参数支持了一个模型，该模型认为传感器的收缩是钙蛋白酶激活过程中涉及的结构变化的一个因素。
